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• HTG Explains: Just How Bad Are Android Tablet Apps?

  - by Chris Hoffman

  Apple loves to criticize the state of Android tablet apps when pushing its own iPad tablets. But just how bad is the Android tablet app situation? Should you avoid Android tablets like the Nexus 7 because of the apps? It’s clear that Apple’s iPad is way ahead when it comes to the sheer quantity of tablet-optimized apps. It’s also clear that some popular apps — particularly touch-optimized games — only show up on iPad. But that’s not the whole story. The Basics First, let’s get an idea of the basic stuff that will work well for you on Android. An excellent web browser. Chrome has struggled with performance on Android, but hits its stride on the Nexus 7 (2013). Great, tablet-optimized apps for all of Google’s services, from YouTube to Gmail and Google Maps. Everything you need for reading, from Amazon’s Kindle app for eBooks, Flipboard and Feedly for new articles from websites, and other services like the popular Pocket read-it-later service. Apps for most popular media services, from Netflix, Hulu, and YouTube for videos to Pandora, Spotify, and Rdio for music. A few things aren’t available — you won’t find Apple’s iTunes and Amazon still doesn’t offer an Amazon Instant Video app for Android, while they do for iPad and even their own Android-based Kindle Fire devices. Android has very good app coverage when it comes to consuming content, whether you’re reading websites and ebooks or watching videos and listening to music. You can play almost any Android smartphone game, too. For content consumption, Android is better than something like Windows 8, which lacks apps for Google services like YouTube and still doesn’t have apps for popular media services like Spotify and Rdio. How Android Scales Smartphone Apps Let’s look at how Android scales smartphone apps. Now, bear with us here — we know “scaling” is a dirty word considering how poorly Apple’s iPad scales iPhone apps, but it’s not as bad on Android. When an iPad runs an iPhone app, it simply doubles the pixels and effectively zooms in. For example, if you had  Twitter app with five tweets visible at once on an iPhone and ran the same app on an iPad, the iPad would simply “zoom in” and enlarge the same screen — you’d still see five tweets, but each tweet would appear larger. This is why developers create optimized iPad apps with their own interfaces. It’s especially important on Apple’s iOS. Android devices come in all shapes and sizes, so Android apps have a smarter, more intelligent way to adapt to different screen sizes. Let’s say you have a Twitter app designed for smartphones and it only shows five tweets at once when run on a phone. If you ran the same app on a tablet, you wouldn’t see the same five tweets — you’d see ten or more tweets. Rather than simply zooming in, the app can show more content at the same time on a tablet, even if it was never optimized for tablet-size screens. While apps designed for smartphones aren’t generally ideal, they adapt much better on Android than they do on an iPad. This is particularly true when it comes to games. You’re capable of playing almost any Android smartphone game on an Android tablet, and games generally adapt very well to the larger screen. This gives you access to a huge catalog of games. It’s a great option to have, especially when you look at Microsoft’s Window 8 and consider how much better the touch-based app and game selection would be if Microsoft allowed its users to run Windows Phone games on Windows 8. 7-inch vs 10-inch Tablets The Twitter example above wasn’t just an example. The official Twitter app for Android still doesn’t have a tablet-optimized interface, so this is the sort of situation you’d have to deal with on an Android tablet. On the popular Nexus 7, Twitter is an example of a smartphone app that actually works fairly well — in portrait mode, you can see many more tweets on screen at the same time and none of the space really feels all that wasted. This is important to consider — smartphone apps like Twitter often scale quite well to 7-inch screens because a 7-inch screen is much closer in form factor to a smartphone than a 10-inch screen is. When you begin to look at 10-inch Android tablets that are the same size as an iPad, the situation changes. While the Twitter app works well enough on a Nexus 7, it looks horrible on a Nexus 10 or other 10-inch tablet. Running many smartphone-designed apps — possible with the exception of games — on a 10-inch tablet is a frustrating, poor experience. There’s much more white, empty space in the interface. It feels like you’re using a smartphone app on a large screen, and what’s the point of that? A tablet-optimized Twitter app for Android is finally on its way, but this same situation will repeat with many other types of apps. For example, Facebook doesn’t offer a tablet-optimized interface, but it’s okay on a Nexus 7 anyway. On a 10-inch screen, it probably wouldn’t be anywhere near as nice an experience. It goes without saying that Facebook and Twitter both offer iPad apps with interfaces designed for a tablet-size screen. Here’s another problematic app — the official Yelp app for Android. Even just using it on a 7-inch Nexus 7 will be a poor experience, while it would be much worse on a larger 10-inch tablet app. Now, it’s true that many — maybe even most — of the popular apps you might want to run today are optimized for Android tablets. But, when you look at the situation when it comes to popular apps like Twitter, Facebook, and Yelp, it’s clear Android is still behind in a meaningful way. Price Let’s be honest. The thing that really makes Android tablets compelling — and the only reason Android tablets started seeing real traction after years of almost complete dominance by Apple’s iPads — is that Android tablets are available for so much cheaper than iPads. Google’s latest Nexus 7 (2013) is available for only $230. Apple’s non-retina iPad Mini is available at $300, which is already $70 more. In spite of that, the iPad Mini has much older, slower internals and a much lower resolution screen. It’s not as nice to look at when it comes to reading or watching movies, and the iPad Mini reportedly struggles to run Apple’s latest iOS 7. In contrast, the new Nexus 7 has a very high resolution screen, speedy internals, and runs Android very well with little-to-no lag in real use. We haven’t had any problems with it, unlike all the problems we unfortunately encountered with the first Nexus 7. For a really comparable experience to the current Nexus 7, you’d want to get one of Apple’s new retina iPad Minis. That would cost you $400, another $170 over the Nexus 7. In fact, it’s possible to regularly find sales on the Nexus 7, so if you waited you could get it for just $200 — half the price of the iPad mini with a comparable screen and internals. (In fairness, the iPad certainly has better hardware — but you won’t feel if it you’re just using your tablet to browse the web, watch videos, and do other typical tablet things.) This makes a tablet like the popular Nexus 7 a very good option for budget-conscious users who just want a high-quality device they can use to browse the web, watch videos, play games, and generally do light computing. There’s a reason we’re focusing on the Nexus 7 here. The combination of price and size brings it to a very good place. It’s awfully cheap for the high-quality experience you get, and the 7-inch screen means that even the non-tablet-optimized apps you may stumble across will often work fairly well. On the other hand, more expensive 10-inch Android tablets are still a tougher sell. For $400-$500, you’re getting awfully close to Apple’s full-size iPad price range and Android tablets don’t have as good an app ecosystem as an iPad. It’s hard to recommend an expensive, 10-inch Android tablet over a full-size iPad to average users. In summary, the Android app tablet app situation is nowhere near as bad as it was a few years ago. The success of the Nexus 7 proves that Android tablets can be compelling experiences, and there are a wide variety of strong apps. That said, more expensive 10-inch Android tablets that compete directly with the full-size iPad on price still don’t make much sense for most people.  Unless you have a specific reason for preferring an Android tablet, it’s tough not to recommend an iPad if you’re looking at spending $400+ on a 10-inch tablet. Image Credit: Christian Ghanime on Flickr, Christian Ghanime on Flickr     

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• Timeout Considerations for Solicit Response

  - by Michael Stephenson

  Background One of the clients I work with had been experiencing some issues for a while surrounding web service timeouts.  It's been a little challenging to work through the problems due to limitations in the diagnostic information available from one of the applications, but I learned some interesting things while troubleshooting the problem which don't seem to have been discussed much in the community so I thought I'd share my findings. In the scenario we have BizTalk trying to make calls to a .net web service which was exposed as a WSE 2 endpoint.  In the process BizTalk will try to make a large number of concurrent web service calls to the application, and the backend application has more than enough infrastructure and capability to handle the load. We have configured the <ConnectionManagement> section of the BizTalk configuration file to support up to 100 concurrent connections from each of our 2 BizTalk send servers to the web servers of the application. The problem we were facing was that the BizTalk side was reporting a significant number of timeouts when calling the web service.   One of the biggest issues was the challenge of being able to correlate a message from BizTalk to the IIS log in the .net application and the custom logs in the application especially when there was a fairly large number of servers hosting the web services.  However the key moment came when we were able to identify a specific call which had taken 40 seconds to execute on the server (yes a long time I know but that's a different story!).  Anyway we were able to identify that this had timed out on the BizTalk side.  Based on the normal 2 minute timeout we knew something unexpected was going on. From here I decided to do some experimentation and I wanted to start outside of BizTalk because my hunch was this was not a BizTalk behaviour but something which was being highlighted by BizTalk because of our large load.     Server-side - Sample Web Service To begin with I created a sample web service.  Nothing special just a vanilla asmx web service hosted in IIS6 on Windows 2003 Standard Edition.  The web service is just a hello world style web service as shown in the below picture.  The only key feature is that the server side web method has a 30 second sleep in it and will trace out some information before and after the thread is set to sleep.      In the configuration for this web service there again is nothing special it's pretty much the most plain simple web service you could build. Client-Side To begin looking at what was happening with our example I created a number of different ways to consume the web service. SoapHttpClientProtocol Example I created a small application which would use a normal proxy generated to call the web service.  It would iterate around a loop and make calls using the begin/end methods so I can do this asynchronously.  I would do a loop of 20 calls with the ConnectionManager configuration section supporting only 5 concurrent connections to the server.     <connectionManagement> <remove address="*"/> <add address = "*" maxconnection = "12" /> <add address = "http://<ServerName>" maxconnection = "5" />                         </connectionManagement> </system.net>     The below picture shows an example of the service calling code, key points are: I have configured the timeout of 40 seconds for the proxy I am using the asynchronous methods on the proxy to call the web service         The Test I would run the client and execute 21 calls to the web service.   The Results  Below is the client side trace showing what's happening on the client. In the below diagram is the web service side trace showing what's happening on the server Some observations on the results are: All of the calls were successful from the clients perspective You could see the next call starting on the server as soon as the previous one had completed Calls took significantly longer than 40 seconds from the start of our call to the return. In fact call 20 took 2 minutes and 30 seconds from the perspective of my code to execute even though I had set the timeout to 40 seconds     WSE 2 Sample In the second example I used the exact same code to call the web service again with a single exception that I modified the web service proxy to derive from WebServiceClient protocol which is part of WSE 2 (using SP3).  The below picture shows the basic code and the key points are: I have configured the timeout of 40 seconds for the proxy I am using the asynchronous methods on the proxy to call the web service        The Test This test would execute 21 calls from the client to the web service.   The Results  The below trace is from the client side: The below trace is from the server side:   Some observations on the trace results for this scenario are: With call 4 if you look at the server side trace it did not start executing on the server for a number of seconds after the other 4 initial calls which were accepted by the server. I re-ran the test and this happened a couple of times and not on most others so at this point I'm just putting this down to something unexpected happening on the development machine and we will leave this observation out of scope of this article. You can see that the client side trace statement executed almost immediately in all cases All calls after the initial few calls would timeout On the client side the calls that did timeout; timed out in a longer duration than the 40 seconds we set as the timeout You can see that as calls were completing on the server the next calls were starting to come through The calls that timed out on the client did actually connect to the server and their server side execution completed successfully     Elaboration on the findings Based on the above observations I have drawn the below sequence diagram to illustrate conceptually what is happening.  Everything except the final web service object is on the client side of the call. In the diagram below I've put two notes on the Web Service Proxy to show the two different places where the different base classes seem to start their timeout counters. From the earlier samples we can work out that the timeout counter for the WSE web service proxy starts before the one for the SoapHttpClientProtocol proxy and the WSE one includes the time to get a connection from the pool; whereas the Soap proxy timeout just covers the method execution. One interesting observation is if we rerun the above sample and increase the number of calls from 21 to 100,000 then for the WSE sample we will see a similar pattern where everything after the first few calls will timeout on the client as soon as it makes a connection to the server whereas the soap proxy will happily plug away and process all of the calls without a single timeout. I have actually set the sample running overnight and this did happen. At this point you are probably thinking the same thoughts I was at the time about the differences in behaviour and which is right and why are they different? I'm not sure there is a definitive answer to this in the documentation, or at least not that I could find! I think you just have to consider that they are different and they could have different effects depending on your messaging solution. In lots of situations this is just not an issue as your concurrent requests doesn't get to the situation where you end up throttling the web service calls on the client side, however this is definitely more common with an integration broker such as BizTalk where you often have high throughput requirements.  Some of the considerations you should make Based on this behaviour you should be aware of the following: In a .net application if you are making lots of concurrent web service calls from an application in an asynchronous manner your user may thing they are experiencing poor performance but you think your web service is working well. The problem could be that the client will have a default of 2 connections to remote servers so you should bear this in mind When you are developing a BizTalk solution or a .net solution with the WSE 2 stack you may experience timeouts under load and throttling the number of connections using the max connections element in the configuration file will not help you For an application using WSE2 or SoapHttpClientProtocol an expired timeout will not throw an error until after a connection to the server has been made so you should consider this in your transaction and durability patterns     Our Work Around In the short term for our specific scenario we know that we can handle this by just increasing our timeout value.  There is only a specific small window when we get lots of concurrent traffic that causes this scenario so we should be able to increase the timeout to take into consideration the additional client side wait, and on the odd occasion where we do get a timeout the BizTalk send port retry will handle this. What was causing our original problem was that for that short window we were getting a lot of retries which significantly increased the load on our send servers and highlighted the issue.  Longer Term Solution As a longer term solution this really gives us more ammunition to argue a migration to WCF. The application we are calling has some factors which limit the protocols we can use but with WCF we would have more control on the various timeout options because in WCF you can configure specific parts of the timeout. Summary I've had this blog post on my to do list for ages but hopefully it will be useful to some people to just understand this behaviour and to possibly help you with some performance issues you may have. I do not believe there is too much in the way of documentation particularly around WSE2 and ASMX in this area so again another bit of ammunition for migrating to WCF. I'll try to do a follow up post with the sample for WCF to show how this changes things.

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• Processing Kinect v2 Color Streams in Parallel

  - by Chris Gardner

  Originally posted on: http://geekswithblogs.net/freestylecoding/archive/2014/08/20/processing-kinect-v2-color-streams-in-parallel.aspxProcessing Kinect v2 Color Streams in Parallel I've really been enjoying being a part of the Kinect for Windows Developer's Preview. The new hardware has some really impressive capabilities. However, with great power comes great system specs. Unfortunately, my little laptop that could is not 100% up to the task; I've had to get a little creative. The most disappointing thing I've run into is that I can't always cleanly display the color camera stream in managed code. I managed to strip the code down to what I believe is the bear minimum: using( ColorFrame _ColorFrame = e.FrameReference.AcquireFrame() ) { if( null == _ColorFrame ) return;   BitmapToDisplay.Lock(); _ColorFrame.CopyConvertedFrameDataToIntPtr( BitmapToDisplay.BackBuffer, Convert.ToUInt32( BitmapToDisplay.BackBufferStride * BitmapToDisplay.PixelHeight ), ColorImageFormat.Bgra ); BitmapToDisplay.AddDirtyRect( new Int32Rect( 0, 0, _ColorFrame.FrameDescription.Width, _ColorFrame.FrameDescription.Height ) ); BitmapToDisplay.Unlock(); } With this snippet, I'm placing the converted Bgra32 color stream directly on the BackBuffer of the WriteableBitmap. This gives me pretty smooth playback, but I still get the occasional freeze for half a second. After a bit of profiling, I discovered there were a few problems. The first problem is the size of the buffer along with the conversion on the buffer. At this time, the raw image format of the data from the Kinect is Yuy2. This is great for direct video processing. It would be ideal if I had a WriteableVideo object in WPF. However, this is not the case. Further digging led me to the real problem. It appears that the SDK is converting the input serially. Let's think about this for a second. The color camera is a 1080p camera. As we should all know, this give us a native resolution of 1920 x 1080. This produces 2,073,600 pixels. Yuy2 uses 4 bytes per 2 pixel, for a buffer size of 4,147,200 bytes. Bgra32 uses 4 bytes per pixel, for a buffer size of 8,294,400 bytes. The SDK appears to be doing this on one thread. I started wondering if I chould do this better myself. I mean, I have 8 cores in my system. Why can't I use them all? The first problem is converting a Yuy2 frame into a Bgra32 frame. It is NOT trivial. I spent a day of research of just how to do this. In the end, I didn't even produce the best algorithm possible, but it did work. After I managed to get that to work, I knew my next step was the get the conversion operation off the UI Thread. This was a simple process of throwing the work into a Task. Of course, this meant I had to marshal the final write to the WriteableBitmap back to the UI thread. Finally, I needed to vectorize the operation so I could run it safely in parallel. This was, mercifully, not quite as hard as I thought it would be. I had my loop return an index to a pair of pixels. From there, I had to tell the loop to do everything for this pair of pixels. If you're wondering why I did it for pairs of pixels, look back above at the specification for the Yuy2 format. I won't go into full detail on why each 4 bytes contains 2 pixels of information, but rest assured that there is a reason why the format is described in that way. The first working attempt at this algorithm successfully turned my poor laptop into a space heater. I very quickly brought and maintained all 8 cores up to about 97% usage. That's when I remembered that obscure option in the Task Parallel Library where you could limit the amount of parallelism used. After a little trial and error, I discovered 4 parallel tasks was enough for most cases. This yielded the follow code: private byte ClipToByte( int p_ValueToClip ) { return Convert.ToByte( ( p_ValueToClip < byte.MinValue ) ? byte.MinValue : ( ( p_ValueToClip > byte.MaxValue ) ? byte.MaxValue : p_ValueToClip ) ); }   private void ColorFrameArrived( object sender, ColorFrameArrivedEventArgs e ) { if( null == e.FrameReference ) return;   // If you do not dispose of the frame, you never get another one... using( ColorFrame _ColorFrame = e.FrameReference.AcquireFrame() ) { if( null == _ColorFrame ) return;   byte[] _InputImage = new byte[_ColorFrame.FrameDescription.LengthInPixels * _ColorFrame.FrameDescription.BytesPerPixel]; byte[] _OutputImage = new byte[BitmapToDisplay.BackBufferStride * BitmapToDisplay.PixelHeight]; _ColorFrame.CopyRawFrameDataToArray( _InputImage );   Task.Factory.StartNew( () => { ParallelOptions _ParallelOptions = new ParallelOptions(); _ParallelOptions.MaxDegreeOfParallelism = 4;   Parallel.For( 0, Sensor.ColorFrameSource.FrameDescription.LengthInPixels / 2, _ParallelOptions, ( _Index ) => { // See http://msdn.microsoft.com/en-us/library/windows/desktop/dd206750(v=vs.85).aspx int _Y0 = _InputImage[( _Index << 2 ) + 0] - 16; int _U = _InputImage[( _Index << 2 ) + 1] - 128; int _Y1 = _InputImage[( _Index << 2 ) + 2] - 16; int _V = _InputImage[( _Index << 2 ) + 3] - 128;   byte _R = ClipToByte( ( 298 * _Y0 + 409 * _V + 128 ) >> 8 ); byte _G = ClipToByte( ( 298 * _Y0 - 100 * _U - 208 * _V + 128 ) >> 8 ); byte _B = ClipToByte( ( 298 * _Y0 + 516 * _U + 128 ) >> 8 );   _OutputImage[( _Index << 3 ) + 0] = _B; _OutputImage[( _Index << 3 ) + 1] = _G; _OutputImage[( _Index << 3 ) + 2] = _R; _OutputImage[( _Index << 3 ) + 3] = 0xFF; // A   _R = ClipToByte( ( 298 * _Y1 + 409 * _V + 128 ) >> 8 ); _G = ClipToByte( ( 298 * _Y1 - 100 * _U - 208 * _V + 128 ) >> 8 ); _B = ClipToByte( ( 298 * _Y1 + 516 * _U + 128 ) >> 8 );   _OutputImage[( _Index << 3 ) + 4] = _B; _OutputImage[( _Index << 3 ) + 5] = _G; _OutputImage[( _Index << 3 ) + 6] = _R; _OutputImage[( _Index << 3 ) + 7] = 0xFF; } );   Application.Current.Dispatcher.Invoke( () => { BitmapToDisplay.WritePixels( new Int32Rect( 0, 0, Sensor.ColorFrameSource.FrameDescription.Width, Sensor.ColorFrameSource.FrameDescription.Height ), _OutputImage, BitmapToDisplay.BackBufferStride, 0 ); } ); } ); } } This seemed to yield a results I wanted, but there was still the occasional stutter. This lead to what I realized was the second problem. There is a race condition between the UI Thread and me locking the WriteableBitmap so I can write the next frame. Again, I'm writing approximately 8MB to the back buffer. Then, I started thinking I could cheat. The Kinect is running at 30 frames per second. The WPF UI Thread runs at 60 frames per second. This made me not feel bad about exploiting the Composition Thread. I moved the bulk of the code from the FrameArrived handler into CompositionTarget.Rendering. Once I was in there, I polled from a frame, and rendered it if it existed. Since, in theory, I'm only killing the Composition Thread every other hit, I decided I was ok with this for cases where silky smooth video performance REALLY mattered. This ode looked like this: private byte ClipToByte( int p_ValueToClip ) { return Convert.ToByte( ( p_ValueToClip < byte.MinValue ) ? byte.MinValue : ( ( p_ValueToClip > byte.MaxValue ) ? byte.MaxValue : p_ValueToClip ) ); }   void CompositionTarget_Rendering( object sender, EventArgs e ) { using( ColorFrame _ColorFrame = FrameReader.AcquireLatestFrame() ) { if( null == _ColorFrame ) return;   byte[] _InputImage = new byte[_ColorFrame.FrameDescription.LengthInPixels * _ColorFrame.FrameDescription.BytesPerPixel]; byte[] _OutputImage = new byte[BitmapToDisplay.BackBufferStride * BitmapToDisplay.PixelHeight]; _ColorFrame.CopyRawFrameDataToArray( _InputImage );   ParallelOptions _ParallelOptions = new ParallelOptions(); _ParallelOptions.MaxDegreeOfParallelism = 4;   Parallel.For( 0, Sensor.ColorFrameSource.FrameDescription.LengthInPixels / 2, _ParallelOptions, ( _Index ) => { // See http://msdn.microsoft.com/en-us/library/windows/desktop/dd206750(v=vs.85).aspx int _Y0 = _InputImage[( _Index << 2 ) + 0] - 16; int _U = _InputImage[( _Index << 2 ) + 1] - 128; int _Y1 = _InputImage[( _Index << 2 ) + 2] - 16; int _V = _InputImage[( _Index << 2 ) + 3] - 128;   byte _R = ClipToByte( ( 298 * _Y0 + 409 * _V + 128 ) >> 8 ); byte _G = ClipToByte( ( 298 * _Y0 - 100 * _U - 208 * _V + 128 ) >> 8 ); byte _B = ClipToByte( ( 298 * _Y0 + 516 * _U + 128 ) >> 8 );   _OutputImage[( _Index << 3 ) + 0] = _B; _OutputImage[( _Index << 3 ) + 1] = _G; _OutputImage[( _Index << 3 ) + 2] = _R; _OutputImage[( _Index << 3 ) + 3] = 0xFF; // A   _R = ClipToByte( ( 298 * _Y1 + 409 * _V + 128 ) >> 8 ); _G = ClipToByte( ( 298 * _Y1 - 100 * _U - 208 * _V + 128 ) >> 8 ); _B = ClipToByte( ( 298 * _Y1 + 516 * _U + 128 ) >> 8 );   _OutputImage[( _Index << 3 ) + 4] = _B; _OutputImage[( _Index << 3 ) + 5] = _G; _OutputImage[( _Index << 3 ) + 6] = _R; _OutputImage[( _Index << 3 ) + 7] = 0xFF; } );   BitmapToDisplay.WritePixels( new Int32Rect( 0, 0, Sensor.ColorFrameSource.FrameDescription.Width, Sensor.ColorFrameSource.FrameDescription.Height ), _OutputImage, BitmapToDisplay.BackBufferStride, 0 ); } }

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• On REST: WADL or not IDL, is the following approach right ?

  - by redben

  This question is a bit long, please bear with me. In REST, i think we should not need WADL or any IDL. But rather something that would implicitly cover its concept. The way I think about it is when we (humans) surf the Web, when we go to a web site for the first time, we don't know what services it provides. You discover those on the html home page (or a sitemap page in a help section) or maybe just the main menu on the home page. If you make an analogy, the homepage or site map to us humans is what WSDL is to WS-* or what WADL could be to a REST service. Only that its just like any other html content. I think that in REST the following is a good way to do things, respecting the HATEOS paradigm. Have a top level (or default) resource that lists links to your other resources. For a library example, say RestLibrary.com/ it could be something like: <root xmlns:lib="http://librarystandards.com/libraryml"> <resource class="lib:book"> <link type="application/vnd.libraryml+xml" template="mylib.com/book/{isbn}" /> <link type="application/vnd.libraryml+xml" rel="add" href="mylib.com/book" method="POST" /> <link type="application/vnd.libraryml+xml" rel="update" template="mylib.com/book/{isbn}" method="PUT" /> </resource> <resource class="lib:bookList"> <link template="mylib.com/book?keywords={keywords}" type="application/vnd.openlibrary+xml" rel="search" /> </resource> </root> Note that it is assumed that the media type "application/vnd.libraryml+xml" is a defined standard or (may be just proprietary vocabulary) named libraryml. Also, the client should be able to understand this "homepage" resource (elements root, resource and link). This is the part that could be used instead of WADL : an Abstract vocabulary that should be understandable by any client. You could use an existing standard like Atom for example. But the main idea is to have an abstract vocabulary understandable by any client. Why not WADL then ? well wadl is only for service discovery. The idea here is to have an light abstract vocabulary that would serve as a base for hypermedia. A "root" vocabulary. Like in owl we have owl:thing...etc Now if the client knows the "libraryml" standard it can follow the links to the things it understands (after parsing the media type properties and xmlns). If not, it just won't. When i can't understand how to deal with something in REST architecture i tend to see how we Humans do it in the Web. In the Web, we have the Generic language that is HTML that enables site builders to deliver any specific content, regardless of its meaning to the client (the user), Browsers understand HTML but not the "meaning" of its content. It is the user that understands the (domain specific) content. If i go to say QuantumPhysics.org, my browser can render the home page (it is just html after all) and i can read the home page. If i understand quantum then fine i can continue browsing. If i don't i just get out (unless i want to learn the hardway :) ) In the RetsLibrary.com example the client app is just like me+my browser on QuantumPhysics.org. the media type "application/vnd.libraryml+xml" is quantum physics (knowledge). http is http in both examples. Now HTML of QuantumPhysics.org is in RestLibrary.com is XML + that tiny little abstract vocabulary (root resource and link, that you could replace with something like Atom). So does this approach have any value ? don't we need a root tiny hyper-vocabulary so we can succeed with hypermedia and the "initial URI" concept ? edit Yeah why not RDF as the root vocabulary !

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• ASP.NET MVC 2 "value" in DataAnnotation attribute passed is null, when incorrect date is submitted.

  - by goldenelf2

  Hello to all! This is my first question here on stack overflow. i need help on a problem i encountered during an ASP.NET MVC2 project i am currently working on. I should note that I'm relatively new to MVC design, so pls bear my ignorance. Here goes : I have a regular form on which various details about a person are shown. One of them is "Date of Birth". My view is like this <div class="form-items"> <%: Html.Label("DateOfBirth", "Date of Birth:") %> <%: Html.EditorFor(m => m.DateOfBirth) %> <%: Html.ValidationMessageFor(m => m.DateOfBirth) %> </div> I'm using an editor template i found, to show only the date correctly : <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<System.DateTime?>"%> <%= Html.TextBox("", (Model.HasValue ? Model.Value.ToShortDateString() : string.Empty))%> I used LinqToSql designer to create my model from an sql database. In order to do some validation i made a partial class Person to extend the one created by the designer (under the same namespace) : [MetadataType(typeof(IPerson))] public partial class Person : IPerson { //To create buddy class } public interface IPerson { [Required(ErrorMessage="Please enter a name")] string Name { get; set; } [Required(ErrorMessage="Please enter a surname")] string Surname { get; set; } [Birthday] DateTime? DateOfBirth { get; set; } [Email(ErrorMessage="Please enter a valid email")] string Email { get; set; } } I want to make sure that a correct date is entered. So i created a custom DataAnnotation attribute in order to validate the date : public class BirthdayAttribute : ValidationAttribute { private const string _errorMessage = "Please enter a valid date"; public BirthdayAttribute() : base(_errorMessage) { } public override bool IsValid(object value) { if (value == null) { return true; } DateTime temp; bool result = DateTime.TryParse(value.ToString(), out temp); return result; } } Well, my problem is this. Once i enter an incorrect date in the DateOfBirth field then no custom message is displayed even if use the attribute like [Birthday(ErrorMessage=".....")]. The message displayed is the one returned from the db ie "The value '32/4/1967' is not valid for DateOfBirth.". I tried to enter some break points around the code, and found out that the "value" in attribute is always null when the date is incorrect, but always gets a value if the date is in correct format. The same ( value == null) is passed also in the code generated by the designer. This thing is driving me nuts. Please can anyone help me deal with this? Also if someone can tell me where exactly is the point of entry from the view to the database. Is it related to the model binder? because i wanted to check exactly what value is passed once i press the "submit" button. Thank you.

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• How to pre-load all deployed assemblies for an AppDomain

  - by Andras Zoltan

  Given an App Domain, there are many different locations that Fusion (the .Net assembly loader) will probe for a given assembly. Obviously, we take this functionality for granted and, since the probing appears to be embedded within the .Net runtime (Assembly._nLoad internal method seems to be the entry-point when Reflect-Loading - and I assume that implicit loading is probably covered by the same underlying algorithm), as developers we don't seem to be able to gain access to those search paths. My problem is that I have a component that does a lot of dynamic type resolution, and which needs to be able to ensure that all user-deployed assemblies for a given AppDomain are pre-loaded before it starts its work. Yes, it slows down startup - but the benefits we get from this component totally outweight this. The basic loading algorithm I've already written is as follows. It deep-scans a set of folders for any .dll (.exes are being excluded at the moment), and uses Assembly.LoadFrom to load the dll if it's AssemblyName cannot be found in the set of assemblies already loaded into the AppDomain (this is implemented inefficiently, but it can be optimized later): void PreLoad(IEnumerable<string> paths) { foreach(path p in paths) { PreLoad(p); } } void PreLoad(string p) { //all try/catch blocks are elided for brevity string[] files = null; files = Directory.GetFiles(p, "*.dll", SearchOption.AllDirectories); AssemblyName a = null; foreach (var s in files) { a = AssemblyName.GetAssemblyName(s); if (!AppDomain.CurrentDomain.GetAssemblies().Any( assembly => AssemblyName.ReferenceMatchesDefinition( assembly.GetName(), a))) Assembly.LoadFrom(s); } } LoadFrom is used because I've found that using Load() can lead to duplicate assemblies being loaded by Fusion if, when it probes for it, it doesn't find one loaded from where it expects to find it. So, with this in place, all I now have to do is to get a list in precedence order (highest to lowest) of the search paths that Fusion is going to be using when it searches for an assembly. Then I can simply iterate through them. The GAC is irrelevant for this, and I'm not interested in any environment-driven fixed paths that Fusion might use - only those paths that can be gleaned from the AppDomain which contain assemblies expressly deployed for the app. My first iteration of this simply used AppDomain.BaseDirectory. This works for services, form apps and console apps. It doesn't work for an Asp.Net website, however, since there are at least two main locations - the AppDomain.DynamicDirectory (where Asp.Net places it's dynamically generated page classes and any assemblies that the Aspx page code references), and then the site's Bin folder - which can be discovered from the AppDomain.SetupInformation.PrivateBinPath property. So I now have working code for the most basic types of apps now (Sql Server-hosted AppDomains are another story since the filesystem is virtualised) - but I came across an interesting issue a couple of days ago where this code simply doesn't work: the nUnit test runner. This uses both Shadow Copying (so my algorithm would need to be discovering and loading them from the shadow-copy drop folder, not from the bin folder) and it sets up the PrivateBinPath as being relative to the base directory. And of course there are loads of other hosting scenarios that I probably haven't considered; but which must be valid because otherwise Fusion would choke on loading the assemblies. I want to stop feeling around and introducing hack upon hack to accommodate these new scenarios as they crop up - what I want is, given an AppDomain and its setup information, the ability to produce this list of Folders that I should scan in order to pick up all the DLLs that are going to be loaded; regardless of how the AppDomain is setup. If Fusion can see them as all the same, then so should my code. Of course, I might have to alter the algorithm if .Net changes its internals - that's just a cross I'll have to bear. Equally, I'm happy to consider SQL Server and any other similar environments as edge-cases that remain unsupported for now. Any ideas!?

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• NSMutableString leaks on append or replaceOccurrencesOfString

  - by John

  Hello Folks, I know similar questions have been asked time and time again but I ask that you please bear with me as I cannot seem to find an answer that helps. My application has leaks that are driving me out of my mind. Actually, they are not reported as leaks using Leaks, but my net bytes in ObjectAlloc goes up and up and up and never stops, eventually leading to a crash if it goes on long enough (not very long). The problem occurs with NSMutableStrings. I think there is either something fundamental I don't understand about them, or I am facing another problem that I am having difficulty tracking down but keeps hiding behind the NSMutableStrings. Specifically, I am noticing that whenever I append to or perform a replace on a NSMutableString, ObjectAlloc reports what appear to be mismatches in malloc/frees behind the scene when resizing the NSMutableString. I'm sorry to say this is the second time I'm facing this problem - the first time I messed around for hours and hours and finally the problem went away (magic!) but I don't really know why. When I look at the code below (and believe me, I've stared at it for hours) I cannot see the problem. I look at the code and think to myself that I should be fine because I'm releasing the only object for which I am responsible (aString) and that NSMutableString should be taking care of cleaning up after any resizing it does. In the second example, just so you know in case it helps, the string being passed in comes from an ASIHTTPRequest object (it's the responseString) and I don't do anything at all with it. It's being called simply like so ([self DoStuff2:[request responseString]]) and I don't free the request myself either (I'm using a ASINetworkQueue and I assume that the requests are destroyed for me (I tried and caused errors because the request was already being release somewhere else). Also, I know it shouldn't do anything, but I even tried wrapping the code in autorelease pools, which of course did nothing. I should mention that this code is being run inside of an NSOperation. I thought that perhaps I am experiencing problems because NSOperations should create an autorelease pool for themselves, but I've tried that to no avail. Not related to NSMutableString, but I find I also have similar problems using the NSString componentsSeparatedByString method. Sometimes the memory used by the array that gets the separated components is never released. Hmmm...strings in general seem to be somewhat problematic for me it seems. I would appreciate ANY help anyone can provide. If you require more info, I'll be glad to add it. I do promise you that I've struggled with this (and other problems) for weeks and every problem I encounter I research hard and long until I find a solution - this is not an idle request, but a true cry for help! I've written so much code and now I'm trying to seal some small leaks etc and I notice this problem. Honestly, I cannot believe how memory management in Objective C can stump me so at times...I've read Apple's memory mgmt docs many times and I thought I thoroughly understood it and I try to be diligent about releasing objects I own, but sometimes I find myself wondering if I truly understand...I would like to put this to bed once and make sure I understand all this fully - to have this sort of question/problem after writing thousands of lines of code is more than a little scary/embarrassing/annoying. So again, if anybody has any insight, I'd be grateful. Thanks for your time and efforts. -(void)DoStuff { NSString *aString [ [[NSString alloc] initWithFormat:@"text %@ more text", self.strVariable]; [self.someMutableStringVar replaceOccurrencesOfString:@"replace" withString:aString options:NSCaseInsensitiveSearch range:NSMakeRange(0, [self.someMutableStringVar length])]; [aString release]; } -(void)DoStuff2:(NSString *)aString { [self.someMutableStringVar appendString:aString]; }

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• ASP.NET MVC 2 "value" in IsValid override in DataAnnotation attribute passed is null, when incorrect

  - by goldenelf2

  Hello to all! This is my first question here on stack overflow. i need help on a problem i encountered during an ASP.NET MVC2 project i am currently working on. I should note that I'm relatively new to MVC design, so pls bear my ignorance. Here goes : I have a regular form on which various details about a person are shown. One of them is "Date of Birth". My view is like this <div class="form-items"> <%: Html.Label("DateOfBirth", "Date of Birth:") %> <%: Html.EditorFor(m => m.DateOfBirth) %> <%: Html.ValidationMessageFor(m => m.DateOfBirth) %> </div> I'm using an editor template i found, to show only the date correctly : <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<System.DateTime?>"%> <%= Html.TextBox("", (Model.HasValue ? Model.Value.ToShortDateString() : string.Empty))%> I used LinqToSql designer to create my model from an sql database. In order to do some validation i made a partial class Person to extend the one created by the designer (under the same namespace) : [MetadataType(typeof(IPerson))] public partial class Person : IPerson { //To create buddy class } public interface IPerson { [Required(ErrorMessage="Please enter a name")] string Name { get; set; } [Required(ErrorMessage="Please enter a surname")] string Surname { get; set; } [Birthday] DateTime? DateOfBirth { get; set; } [Email(ErrorMessage="Please enter a valid email")] string Email { get; set; } } I want to make sure that a correct date is entered. So i created a custom DataAnnotation attribute in order to validate the date : public class BirthdayAttribute : ValidationAttribute { private const string _errorMessage = "Please enter a valid date"; public BirthdayAttribute() : base(_errorMessage) { } public override bool IsValid(object value) { if (value == null) { return true; } DateTime temp; bool result = DateTime.TryParse(value.ToString(), out temp); return result; } } Well, my problem is this. Once i enter an incorrect date in the DateOfBirth field then no custom message is displayed even if use the attribute like [Birthday(ErrorMessage=".....")]. The message displayed is the one returned from the db ie "The value '32/4/1967' is not valid for DateOfBirth.". I tried to enter some break points around the code, and found out that the "value" in attribute is always null when the date is incorrect, but always gets a value if the date is in correct format. The same ( value == null) is passed also in the code generated by the designer. This thing is driving me nuts. Please can anyone help me deal with this? Also if someone can tell me where exactly is the point of entry from the view to the database. Is it related to the model binder? because i wanted to check exactly what value is passed once i press the "submit" button. Thank you.

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• python: what are efficient techniques to deal with deeply nested data in a flexible manner?

  - by AlexandreS

  My question is not about a specific code snippet but more general, so please bear with me: How should I organize the data I'm analyzing, and which tools should I use to manage it? I'm using python and numpy to analyse data. Because the python documentation indicates that dictionaries are very optimized in python, and also due to the fact that the data itself is very structured, I stored it in a deeply nested dictionary. Here is a skeleton of the dictionary: the position in the hierarchy defines the nature of the element, and each new line defines the contents of a key in the precedent level: [AS091209M02] [AS091209M01] [AS090901M06] ... [100113] [100211] [100128] [100121] [R16] [R17] [R03] [R15] [R05] [R04] [R07] ... [1263399103] ... [ImageSize] [FilePath] [Trials] [Depth] [Frames] [Responses] ... [N01] [N04] ... [Sequential] [Randomized] [Ch1] [Ch2] Edit: To explain a bit better my data set: [individual] ex: [AS091209M02] [imaging session (date string)] ex: [100113] [Region imaged] ex: [R16] [timestamp of file] ex [1263399103] [properties of file] ex: [Responses] [regions of interest in image ] ex [N01] [format of data] ex [Sequential] [channel of acquisition: this key indexes an array of values] ex [Ch1] The type of operations I perform is for instance to compute properties of the arrays (listed under Ch1, Ch2), pick up arrays to make a new collection, for instance analyze responses of N01 from region 16 (R16) of a given individual at different time points, etc. This structure works well for me and is very fast, as promised. I can analyze the full data set pretty quickly (and the dictionary is far too small to fill up my computer's ram : half a gig). My problem comes from the cumbersome manner in which I need to program the operations of the dictionary. I often have stretches of code that go like this: for mk in dic.keys(): for rgk in dic[mk].keys(): for nk in dic[mk][rgk].keys(): for ik in dic[mk][rgk][nk].keys(): for ek in dic[mk][rgk][nk][ik].keys(): #do something which is ugly, cumbersome, non reusable, and brittle (need to recode it for any variant of the dictionary). I tried using recursive functions, but apart from the simplest applications, I ran into some very nasty bugs and bizarre behaviors that caused a big waste of time (it does not help that I don't manage to debug with pdb in ipython when I'm dealing with deeply nested recursive functions). In the end the only recursive function I use regularly is the following: def dicExplorer(dic, depth = -1, stp = 0): '''prints the hierarchy of a dictionary. if depth not specified, will explore all the dictionary ''' if depth - stp == 0: return try : list_keys = dic.keys() except AttributeError: return stp += 1 for key in list_keys: else: print '+%s> [\'%s\']' %(stp * '---', key) dicExplorer(dic[key], depth, stp) I know I'm doing this wrong, because my code is long, noodly and non-reusable. I need to either use better techniques to flexibly manipulate the dictionaries, or to put the data in some database format (sqlite?). My problem is that since I'm (badly) self-taught in regards to programming, I lack practical experience and background knowledge to appreciate the options available. I'm ready to learn new tools (SQL, object oriented programming), whatever it takes to get the job done, but I am reluctant to invest my time and efforts into something that will be a dead end for my needs. So what are your suggestions to tackle this issue, and be able to code my tools in a more brief, flexible and re-usable manner?

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• Internet Explorer percent based layout issue

  - by Tom

  Heya, My goal is to make a layout that is 200% width and height, with four containers of equal height and width (100% each), using no javascript as the bear minimum (or preferably no hacks). Right now I am using HTML5, and CSS display:table. It works fine in Safari 4, Firefox 3.5, and Chrome 5. I haven't tested it yet on older versions. Nonetheless, in IE7 and IE8 this layout fails completely. (I do use the Javascript HTML5 enabling script /cc../, so it should not be the use of new HTML5 tags) Here is what I have: <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta charset="UTF-8" /> <title>IE issue with layout</title> <style type="text/css" media="all"> /* styles */ @import url("reset.css"); /* Generall CSS */ .table { display:table; } .row { display:table-row; } .cell { display:table-cell; } /* Specific CSS */ html, body { //overflow:hidden; I later intend to limit the viewport } section#body { position:absolute; width:200%; height:200%; overflow:hidden; } section#body .row { width:200%; height:50%; overflow:hidden; } section#body .row .cell { width:50%; overflow:hidden; } section#body .row .cell section { display:block; width:100%; height:100%; overflow:hidden; } section#body #stage0 section header { text-align:center; height:20%; display:block; } section#body #stage0 section footer { display:block; height:80%; } </style> </head> <body> <section id="body" class="table"> <section class="row"> <section id="stage0" class="cell"> <section> <header> <form> <input type="text" name="q" /> <input type="submit" value="Search" /> </form> </header> <footer> <table id="scrollers"> </table> </footer> </section> </section> <section id="stage1" class="cell"> <section> content </section> </section> </section> <section class="row"> <section id="stage2" class="cell"> <section> content </section> </section> <section id="stage3" class="cell"> <section> content </section> </section> </section> </section> </body> </html> You can see it live here: http://www.tombarrasso.com/ie-issue/

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• Marshal a C# struct to C++ VARIANT

  - by jortan

  To start with, I'm not very familiar with the COM-technology, this is the first time I'm working with it so bear with me. I'm trying to call a COM-object function from C#. This is the interface in the idl-file: [id(6), helpstring("vConnectInfo=ConnectInfoType")] HRESULT ConnectTarget([in,out] VARIANT* vConnectInfo); This is the interop interface I got after running tlbimp: void ConnectTarget(ref object vConnectInfo); The c++ code in COM object for the target function: STDMETHODIMP PCommunication::ConnectTarget(VARIANT* vConnectInfo) { if (!((vConnectInfo->vt & VT_ARRAY) && (vConnectInfo->vt & VT_BYREF))) { return E_INVALIDARG; } ConnectInfoType *pConnectInfo = (ConnectInfoType *)((*vConnectInfo->pparray)->pvData); ... } This COM-object is running in another process, it is not in a dll. I can add that the COM object is also used from another program written in C++. In that case there is no problem because in C++ a VARIANT is created and pparray-pvData is set to the connInfo data-structure and then the COM-object is called with the VARIANT as parameter. In C#, as I understand, my struct should be marshalled as a VARIANT automatically. These are two methods I've been using (or actually I've tried a lot more...) to call this method from C#: private void method1_Click(object sender, EventArgs e) { pcom.PCom PCom = new pcom.PCom(); pcom.IGeneralManagementServices mgmt = (pcom.IGeneralManagementServices)PCom; m_ci = new ConnectInfoType(); fillConnInfo(ref m_ci); mgmt.ConnectTarget(m_ci); } In the above case the struct gets marshalled as VT_UNKNOWN. This is a simple case and works if the parameter is not a struct (eg. works for int). private void method4_Click(object sender, EventArgs e) { ConnectInfoType ci = new ConnectInfoType(); fillConnInfo(ref ci); pcom PCom = new pcom.PCom(); pcom.IGeneralManagementServices mgmt = (pcom.IGeneralManagementServices)PCom; ParameterModifier[] pms = new ParameterModifier[1]; ParameterModifier pm = new ParameterModifier(1); pm[0] = true; pms[0] = pm; object[] param = new object[1]; param[0] = ci; object[] args = new object[1]; args[0] = param; mgmt.GetType().InvokeMember("ConnectTarget", BindingFlags.InvokeMethod, null, mgmt, args, pms, null, null); } In this case it gets marshalled as VT_ARRAY | VT_BYREF | VT_VARIANT. The problem is that when debugging the "target-function" ConnectTarget I cannot find the data I send in the SAFEARRAY-struct (or in any other place in memory either) What do I do with a VT_VARIANT? Any ideas on how to get my struct-data? Update: The ConnectInfoType struct: [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public class ConnectInfoType { public short network; public short nodeNumber; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 51)] public string connTargPassWord; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] public string sConnectId; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)] public string sConnectPassword; public EnuConnectType eConnectType; public int hConnectHandle; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] public string sAccessPassword; }; And the corresponding struct in c++: typedef struct ConnectInfoType { short network; short nodeNumber; char connTargPassWord[51]; char sConnectId[8]; char sConnectPassword[16]; EnuConnectType eConnectType; int hConnectHandle; char sAccessPassword[8]; } ConnectInfoType;

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• CakeDC Users Plugin - I Can't Send Emails

  - by JimBadger

  I apologise for the rambling nature of this question, please bear with me and I'll provide all the extra info needed for you to stop me going mad from failing at something that looks inherently very straightforward... I've just installed CakePHP 2.2, and the first thing I've done is add the cakeDC Users plugin. It's all working, apart from sending an email verification when a user registers. I've tried so many combinations of different things in email.php, that I have now utterly got my knickers in a twist. Whatever I do, when the verification email should be sent, all I get is: No connection could be made because the target machine actively refused it. My email.php currently looks like this: class EmailConfig { public $default = array( 'transport' => 'Smtp', 'from' => '[email protected]', //'charset' => 'utf-8', //'headerCharset' => 'utf-8', ); public $smtp = array( 'transport' => 'Smtp', 'from' => array('Blah <[email protected]>' => 'Chimp'), 'host' => 'ssl://smtp.gmail.com', 'port' => 465, 'timeout' => 30, 'username' => '[email protected]', 'password' => 'secret', 'client' => null, 'log' => false, //'charset' => 'utf-8', //'headerCharset' => 'utf-8', ); public $fast = array( 'from' => '[email protected]', 'sender' => null, 'to' => null, 'cc' => null, 'bcc' => null, 'replyTo' => null, 'readReceipt' => null, 'returnPath' => null, 'messageId' => true, 'subject' => null, 'message' => null, 'headers' => null, 'viewRender' => null, 'template' => false, 'layout' => false, 'viewVars' => null, 'attachments' => null, 'emailFormat' => null, 'transport' => 'Smtp', 'host' => 'blah.net', 'port' => 25, 'timeout' => 30, 'username' => 'user', 'password' => 'secret', 'client' => null, 'log' => true, //'charset' => 'utf-8', //'headerCharset' => 'utf-8', ); } How do I get cakeDC Users plugin to just send a non-SMTP email? Or do I have to use, for example, my Gmail details? But, if I do have to go down the SMTP route, what is wrong with the above? Other info: I'm using the latest version of XAMPP and my PHP install is ssl enabled.

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• Android SQLlite crashes after trying retrieving data from it

  - by Pavel

  Hey everyone. I'm kinda new to android programming so please bear with me. I'm having some problems with retrieving records from the db. Basically, all I want to do is to store latitudes and longitudes which GPS positioning functions outputs and display them in a list using ListActivity on different tab later on. This is how the code for my DBAdapter helper class looks like: public class DBAdapter { public static final String KEY_ROWID = "_id"; public static final String KEY_LATITUDE = "latitude"; public static final String KEY_LONGITUDE = "longitude"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "coords"; private static final String DATABASE_TABLE = "coordsStorage"; private static final int DATABASE_VERSION = 1; private static final String DATABASE_CREATE = "create table coordsStorage (_id integer primary key autoincrement, " + "latitude integer not null, longitude integer not null);"; private final Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db; public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS titles"); onCreate(db); } } //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; } //---closes the database--- public void close() { DBHelper.close(); } //---insert a title into the database--- public long insertCoords(int latitude, int longitude) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_LATITUDE, latitude); initialValues.put(KEY_LONGITUDE, longitude); return db.insert(DATABASE_TABLE, null, initialValues); } //---deletes a particular title--- public boolean deleteTitle(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) 0; } //---retrieves all the titles--- public Cursor getAllTitles() { return db.query(DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, null, null, null, null, null); } //---retrieves a particular title--- public Cursor getTitle(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //---updates a title--- /*public boolean updateTitle(long rowId, int latitude, int longitude) { ContentValues args = new ContentValues(); args.put(KEY_LATITUDE, latitude); args.put(KEY_LONGITUDE, longitude); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) 0; }*/ } Now my question is - am I doing something wrong here? If yes could someone please tell me what? And how I should retrieve the records in organised list manner? Help would be greatly appreciated!!

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• Recursing data into a 2 dimensional array in PHP 5

  - by user315699

  I'm getting bamboozled by "for each" loops and two dimensional arrays, and I'm a php newb so please bear with me (and ignore any variables with the word "image" - it's all about the mp3s, I just didn't change it from the xml tutorial) I found a php function on the net that list files in a directory, the output of which is: Array ( [0] = audio/1.mp3 [1] = audio/2.mp3 [2] = audio/3.mp3 [3] = audio/4.mp3 [4] = audio/5.mp3 ) As expected. And another that lists some info about mp3 files. $mp3datafile = 'audio/1.mp3'; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); print_r($mp3dataArray); unset($mp3dataArray); The output of which is Array ( [Filesize] = 31972 [Encoding] = CBR [etc] ) In order to automatically build RSS for a podcast, I need to generate XML for each item. So far so good. This is how I'm making the xml foreach ($imagearray as $key = $val) { $tnsoundfile = $xml_generator-addChild('item'); $tnsoundfile-addChild('title', $podcasttitle); $enclosure = $tnsoundfile-addChild('enclosure'); $enclosure-addAttribute('url', $val); // that's the filename $enclosure-addAttribute('length', $mp3dataArray[Filesize]); // << Length is file length, not time. But later I also need $mp3dataArray[Length mm:ss] for duration tag. $enclosure-addAttribute('type', 'audio/mpeg'); $tnsoundfile-addChild('guid', $path_to_image_dir.'/'.$val); } (The above has been truncated, I realise it's not proper xml right now, but it was just to show what was going on). Perfect. But I need to do it for as many files as there are in the directory. So, I have an array of the names of the files in the directory in $mp3data And, I have an array of mp3 data in $mp3dataArray from one iteration of the get_metadata() function. If I do the following, then I get a nice list of the mp3 data of the 5 files in the directory: foreach ($mp3data as $key = $val) { $mp3datafile = $val; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); print_r($mp3dataArray); unset($mp3dataArray); } As expected. Where I'm struggling, and have been for most of the day in spite of reading many forums and tutorials, is how to populate the "second dimension" of the array, so that it goes through 1,2,3,4 and 5.mp3 (or however many there are), extracts the metadata, then allows me to use it in the xml section above. Here's what I have foreach ($mp3data as $key = $val) { $mp3datafile = $val; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); $mp3testarray = array($mp3dataArray); } print_r($mp3dataArray); Shouldn't that line print_r($mp3dataArray); give me a nice list of 5 lots of mp3 data, in the way it did when I recursed through the loop as before? Cos this is driving me nuts! It must be something so simple, and any help would be greatly appreciated. Thank you in advance.

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• How to remove the xmlns:XSI and xmlns:XSD namespaces from the xml output of a webservice in .net fra

  - by Chetan

  HI, This is an old question, i have seen some solutions on this forum itself, but am trying to use webservices for the first time so please bear with me on this one. I have a webservice that returns XML in the following format <subs xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" msisdn="965xxxxxx"> <shortcode label="XXXX"> <channels> <channel> <id>442</id> <name>News</name> <billingperiod>7</billingperiod> <billingamount>3</billingamount> <lastbilling>4/14/2010 1:41:11 PM</lastbilling> </channel> <channel> <id>443</id> <name>News2</name> <billingperiod>7</billingperiod> <billingamount>3</billingamount> <lastbilling>4/14/2010 1:41:19 PM</lastbilling> </channel> </channels> </shortcode> </subs> I want the same XMl output without the xmlns:xsd and xmlns:xsi tags. I have tried the following solution that was suggested: Public Function GetSubscription(....) As String Dim namespaces As New XmlSerializerNamespaces namespaces.Add(String.Empty, String.Empty) Dim serializer As New XmlSerializer(SubsDetail.GetType) Dim sw As New System.IO.StringWriter Dim writer As New System.Xml.XmlTextWriter(sw) writer.Formatting = Formatting.None serializer.Serialize(writer, SubsDetail, namespaces) writer.Close() Return sw.toString() The result was that I got an xml in the following format: <string> <?xml version="1.0" encoding="utf-16"?><subs msisdn="965xxxx"> <shortcode label="XXXX"> <channels> <channel> <id>442</id> <name>News</name> <billingperiod>7</billingperiod> <billingamount>3</billingamount> <lastbilling>4/14/2010 1:41:11 PM</lastbilling> </channel> <channel> <id>443</id> <name>News2</name> <billingperiod>7</billingperiod> <billingamount>3</billingamount> <lastbilling>4/14/2010 1:41:19 PM</lastbilling> </channel> </channels> </shortcode> </subs> </string> Though the format of the xml is correct it is coming as string within the <string> tags. This is really driving me nuts. Can I get the output as xml without the outer string tags?

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• Possible iphone animation timing/rendering bug?

  - by David

  Hi all, I have been working on an iphone apps for several weeks. Now I encounter an animation problem that I can't figure out how to resolve. Mayhbe you can help. Here is the details (a little long, bear with me): Basically the effect I want to achieve is, when user click a button, a loading view pops up, hiding the whole screen; and then the apps does a lot of heavy computation, which takes a few seconds. Once the computation is done, soem result views (something likes checkers on a checker board) are rendered under the loading view. Once all result views are rendered, I used animation animation to remove the loading view nand show the result views to the user. Here is what I do: when user click a button, run this code: [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1.0]; [UIView setAnimationBeginsFromCurrentState:YES]; [UIView setAnimationTransition:UIViewAnimationTransitionCurlDown forView:self.view cache:YES]; [UIView setAnimationDelegate:self]; [UIView setAnimationDidStopSelector:@selector(loadingViewInserted:finished:context:)]; // use a really high index number so it will always on top [self.view insertSubview:loadingViewController.view atIndex:1000]; [UIView commitAnimations]; In the "loadingViewInserted" function, it calls another function doing the heavy computation work. Once the computation is done, a lot of result views (like checkers on a checker board) are rendered under the loading view. for(int colIndex = 1; colIndex <= result.columns; colIndex++) { for(int rowIndex = 1; rowIndex <= result.rows; rowIndex++) { ResultView *rv = [ResultView resultViewWithData:results[colIndex][rowIndex]]; [self.view addSubview:rv]; } } Once all result views are added, following animation is invoked to remove the loading view: [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1.0]; [UIView setAnimationBeginsFromCurrentState:YES]; [UIView setAnimationTransition:UIViewAnimationTransitionCurlUp forView:self.view cache:YES]; [loadingViewController.view removeFromSuperview]; [UIView commitAnimations]; By doing this, most of the time (maybe 90%) it does exactly what I want. However, sometime I see some weird result: the loading view shows up first as expected, then before it disappears, some result views, which suppose to be under the loading view, suddenly appears on top of the loading view; and some of them are partial rendered. And then the loading view curled up, and everything looks normal again. The weird situation only lasts for less than a second, but already bad enough to screw up the UI. I have tried all different kinds of thing to fix this (using another thread to remove the loading view, make the loading view non-transparent), but none of them works. The only thing that makes a little better is, I hide all the result views first; after the last animation finished, in its call back, unhide all result views. But this loses the nice effect that when curling up the loading view, the results are already there. At this point, I really think this is a bug in iphone (I compile it with OS 3.0) OS. Or maybe you can point out what I have done wrong (or could do differently). (thanks for finishing this long post, :-) )

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• How can I hit my database with an AJAX call using javascript?

  - by tmedge

  I am pretty new at this stuff, so bear with me. I am using ASP.NET MVC. I have created an overlay to cover the page when someone clicks a button corresponding to a certain database entry. Because of this, ALL of my code for this functionality is in a .js file contained within my project. What I need to do is pull the info corresponding to my entry from the database itself using an AJAX call, and place that into my textboxes. Then, after the end-user has made the desired changes, I need to update that entry's values to match the input. I've been surfing the web for a while, and have failed to find an example that fits my needs effectively. Here is my code in my javascript file thus far: function editOverlay(picId) { //pull up an overlay $('body').append('<div class="overlay" />'); var $overlayClass = $('.overlay'); $overlayClass.append('<div class="dataModal" />'); var $data = $('.dataModal'); overlaySetup($overlayClass, $data); //set up form $data.append('<h1>Edit Picture</h1><br /><br />'); $data.append('Picture name: &nbsp;'); $data.append('<input class="picName" /> <br /><br /><br />'); $data.append('Relative url: &nbsp;'); $data.append('<input class="picRelURL" /> <br /><br /><br />'); $data.append('Description: &nbsp;'); $data.append('<textarea class="picDescription" /> <br /><br /><br />'); var $nameBox = $('.picName'); var $urlBox = $('.picRelURL'); var $descBox = $('.picDescription'); var pic = null; //this is where I need to pull the actual object from the db //var imgList = for (var temp in imgList) { if (temp.Id == picId) { pic= temp; } } /* $nameBox.attr('value', pic.Name); $urlBox.attr('value', pic.RelativeURL); $descBox.attr('value', pic.Description); */ //close buttons $data.append('<input type="button" value="Save Changes" class="saveButton" />'); $data.append('<input type="button" value="Cancel" class="cancelButton" />'); $('.saveButton').click(function() { /* pic.Name = $nameBox.attr('value'); pic.RelativeURL = $urlBox.attr('value'); pic.Description = $descBox.attr('value'); */ //make a call to my Save() method in my repository CloseOverlay(); }); $('.cancelButton').click(function() { CloseOverlay(); }); } The stuff I have commented out is what I need to accomplish and/or is not available until prior issues are resolved. Any and all advice is appreciated! Remember, I am VERY new to this stuff (two weeks, to be exact) and will probably need highly explicit instructions. BTW: overlaySetup() and CloseOverlay() are functions I have living someplace else. Thanks!

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• How to call virtual function of an object in C++

  - by SoonDead

  I'm struggling with calling a virtual function in C++. I'm not experienced in C++, I mainly use C# and Java so I might have some delusions, but bear with me. I have to write a program where I have to avoid dynamic memory allocation if possible. I have made a class called List: template <class T> class List { public: T items[maxListLength]; int length; List() { length = 0; } T get(int i) const { if (i >= 0 && i < length) { return items[i]; } else { throw "Out of range!"; } }; // set the value of an already existing element void set(int i, T p) { if (i >= 0 && i < length) { items[i] = p; } else { throw "Out of range!"; } } // returns the index of the element int add(T p) { if (length >= maxListLength) { throw "Too many points!"; } items[length] = p; return length++; } // removes and returns the last element; T pop() { if (length > 0) { return items[--length]; } else { throw "There is no element to remove!"; } } }; It just makes an array of the given type, and manages the length of it. There is no need for dynamic memory allocation, I can just write: List<Object> objects; MyObject obj; objects.add(obj); MyObject inherits form Object. Object has a virtual function which is supposed to be overridden in MyObject: struct Object { virtual float method(const Input& input) { return 0.0f; } }; struct MyObject: public Object { virtual float method(const Input& input) { return 1.0f; } }; I get the elements as: objects.get(0).method(asdf); The problem is that even though the first element is a MyObject, the Object's method function is called. I'm guessing there is something wrong with storing the object in an array of Objects without dynamically allocating memory for the MyObject, but I'm not sure. Is there a way to call MyObject's method function? How? It's supposed to be a heterogeneous collection btw, so that's why the inheritance is there in the first place. If there is no way to call the MyObject's method function, then how should I make my list in the first place?

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• Use IIS Application Initialization for keeping ASP.NET Apps alive

  - by Rick Strahl

  I've been working quite a bit with Windows Services in the recent months, and well, it turns out that Windows Services are quite a bear to debug, deploy, update and maintain. The process of getting services set up,  debugged and updated is a major chore that has to be extensively documented and or automated specifically. On most projects when a service is built, people end up scrambling for the right 'process' to use for administration. Web app deployment and maintenance on the other hand are common and well understood today, as we are constantly dealing with Web apps. There's plenty of infrastructure and tooling built into Web Tools like Visual Studio to facilitate the process. By comparison Windows Services or anything self-hosted for that matter seems convoluted.In fact, in a recent blog post I mentioned that on a recent project I'd been using self-hosting for SignalR inside of a Windows service, because the application is in fact a 'service' that also needs to send out lots of messages via SignalR. But the reality is that it could just as well be an IIS application with a service component that runs in the background. Either way you look at it, it's either a Windows Service with a built in Web Server, or an IIS application running a Service application, neither of which follows the standard Service or Web App template.Personally I much prefer Web applications. Running inside of IIS I get all the benefits of the IIS platform including service lifetime management (crash and restart), controlled shutdowns, the whole security infrastructure including easy certificate support, hot-swapping of code and the the ability to publish directly to IIS from within Visual Studio with ease.Because of these benefits we set out to move from the self hosted service into an ASP.NET Web app instead.The Missing Link for ASP.NET as a Service: Auto-LoadingI've had moments in the past where I wanted to run a 'service like' application in ASP.NET because when you think about it, it's so much easier to control a Web application remotely. Services are locked into start/stop operations, but if you host inside of a Web app you can write your own ticket and control it from anywhere. In fact nearly 10 years ago I built a background scheduling application that ran inside of ASP.NET and it worked great and it's still running doing its job today.The tricky part for running an app as a service inside of IIS then and now, is how to get IIS and ASP.NET launched so your 'service' stays alive even after an Application Pool reset. 7 years ago I faked it by using a web monitor (my own West Wind Web Monitor app) I was running anyway to monitor my various web sites for uptime, and having the monitor ping my 'service' every 20 seconds to effectively keep ASP.NET alive or fire it back up after a reload. I used a simple scheduler class that also includes some logic for 'self-reloading'. Hacky for sure, but it worked reliably.Luckily today it's much easier and more integrated to get IIS to launch ASP.NET as soon as an Application Pool is started by using the Application Initialization Module. The Application Initialization Module basically allows you to turn on Preloading on the Application Pool and the Site/IIS App, which essentially fires a request through the IIS pipeline as soon as the Application Pool has been launched. This means that effectively your ASP.NET app becomes active immediately, Application_Start is fired making sure your app stays up and running at all times. All the other features like Application Pool recycling and auto-shutdown after idle time still work, but IIS will then always immediately re-launch the application.Getting started with Application InitializationAs of IIS 8 Application Initialization is part of the IIS feature set. For IIS 7 and 7.5 there's a separate download available via Web Platform Installer. Using IIS 8 Application Initialization is an optional install component in Windows or the Windows Server Role Manager: This is an optional component so make sure you explicitly select it.IIS Configuration for Application InitializationInitialization needs to be applied on the Application Pool as well as the IIS Application level. As of IIS 8 these settings can be made through the IIS Administration console.Start with the Application Pool:Here you need to set both the Start Automatically which is always set, and the StartMode which should be set to AlwaysRunning. Both have to be set - the Start Automatically flag is set true by default and controls the starting of the application pool itself while Always Running flag is required in order to launch the application. Without the latter flag set the site settings have no effect.Now on the Site/Application level you can specify whether the site should pre load: Set the Preload Enabled flag to true.At this point ASP.NET apps should auto-load. This is all that's needed to pre-load the site if all you want is to get your site launched automatically.If you want a little more control over the load process you can add a few more settings to your web.config file that allow you to show a static page while the App is starting up. This can be useful if startup is really slow, so rather than displaying blank screen while the user is fiddling their thumbs you can display a static HTML page instead: <system.webServer> <applicationInitialization remapManagedRequestsTo="Startup.htm" skipManagedModules="true"> <add initializationPage="ping.ashx" /> </applicationInitialization> </system.webServer>This allows you to specify a page to execute in a dry run. IIS basically fakes request and pushes it directly into the IIS pipeline without hitting the network. You specify a page and IIS will fake a request to that page in this case ping.ashx which just returns a simple OK string - ie. a fast pipeline request. This request is run immediately after Application Pool restart, and while this request is running and your app is warming up, IIS can display an alternate static page - Startup.htm above. So instead of showing users an empty loading page when clicking a link on your site you can optionally show some sort of static status page that says, "we'll be right back".  I'm not sure if that's such a brilliant idea since this can be pretty disruptive in some cases. Personally I think I prefer letting people wait, but at least get the response they were supposed to get back rather than a random page. But it's there if you need it.Note that the web.config stuff is optional. If you don't provide it IIS hits the default site link (/) and even if there's no matching request at the end of that request it'll still fire the request through the IIS pipeline. Ideally though you want to make sure that an ASP.NET endpoint is hit either with your default page, or by specify the initializationPage to ensure ASP.NET actually gets hit since it's possible for IIS fire unmanaged requests only for static pages (depending how your pipeline is configured).What about AppDomain Restarts?In addition to full Worker Process recycles at the IIS level, ASP.NET also has to deal with AppDomain shutdowns which can occur for a variety of reasons:Files are updated in the BIN folderWeb Deploy to your siteweb.config is changedHard application crashThese operations don't cause the worker process to restart, but they do cause ASP.NET to unload the current AppDomain and start up a new one. Because the features above only apply to Application Pool restarts, AppDomain restarts could also cause your 'ASP.NET service' to stop processing in the background.In order to keep the app running on AppDomain recycles, you can resort to a simple ping in the Application_End event:protected void Application_End() { var client = new WebClient(); var url = App.AdminConfiguration.MonitorHostUrl + "ping.aspx"; client.DownloadString(url); Trace.WriteLine("Application Shut Down Ping: " + url); }which fires any ASP.NET url to the current site at the very end of the pipeline shutdown which in turn ensures that the site immediately starts back up.Manual Configuration in ApplicationHost.configThe above UI corresponds to the following ApplicationHost.config settings. If you're using IIS 7, there's no UI for these flags so you'll have to manually edit them.When you install the Application Initialization component into IIS it should auto-configure the module into ApplicationHost.config. Unfortunately for me, with Mr. Murphy in his best form for me, the module registration did not occur and I had to manually add it.<globalModules> <add name="ApplicationInitializationModule" image="%windir%\System32\inetsrv\warmup.dll" /> </globalModules>Most likely you won't need ever need to add this, but if things are not working it's worth to check if the module is actually registered.Next you need to configure the ApplicationPool and the Web site. The following are the two relevant entries in ApplicationHost.config.<system.applicationHost> <applicationPools> <add name="West Wind West Wind Web Connection" autoStart="true" startMode="AlwaysRunning" managedRuntimeVersion="v4.0" managedPipelineMode="Integrated"> <processModel identityType="LocalSystem" setProfileEnvironment="true" /> </add> </applicationPools> <sites> <site name="Default Web Site" id="1"> <application path="/MPress.Workflow.WebQueueMessageManager" applicationPool="West Wind West Wind Web Connection" preloadEnabled="true"> <virtualDirectory path="/" physicalPath="C:\Clients\…" /> </application> </site> </sites> </system.applicationHost>On the Application Pool make sure to set the autoStart and startMode flags to true and AlwaysRunning respectively. On the site make sure to set the preloadEnabled flag to true.And that's all you should need. You can still set the web.config settings described above as well.ASP.NET as a Service?In the particular application I'm working on currently, we have a queue manager that runs as standalone service that polls a database queue and picks out jobs and processes them on several threads. The service can spin up any number of threads and keep these threads alive in the background while IIS is running doing its own thing. These threads are newly created threads, so they sit completely outside of the IIS thread pool. In order for this service to work all it needs is a long running reference that keeps it alive for the life time of the application.In this particular app there are two components that run in the background on their own threads: A scheduler that runs various scheduled tasks and handles things like picking up emails to send out outside of IIS's scope and the QueueManager. Here's what this looks like in global.asax:public class Global : System.Web.HttpApplication { private static ApplicationScheduler scheduler; private static ServiceLauncher launcher; protected void Application_Start(object sender, EventArgs e) { // Pings the service and ensures it stays alive scheduler = new ApplicationScheduler() { CheckFrequency = 600000 }; scheduler.Start(); launcher = new ServiceLauncher(); launcher.Start(); // register so shutdown is controlled HostingEnvironment.RegisterObject(launcher); }}By keeping these objects around as static instances that are set only once on startup, they survive the lifetime of the application. The code in these classes is essentially unchanged from the Windows Service code except that I could remove the various overrides required for the Windows Service interface (OnStart,OnStop,OnResume etc.). Otherwise the behavior and operation is very similar.In this application ASP.NET serves two purposes: It acts as the host for SignalR and provides the administration interface which allows remote management of the 'service'. I can start and stop the service remotely by shutting down the ApplicationScheduler very easily. I can also very easily feed stats from the queue out directly via a couple of Web requests or (as we do now) through the SignalR service.Registering a Background Object with ASP.NETNotice also the use of the HostingEnvironment.RegisterObject(). This function registers an object with ASP.NET to let it know that it's a background task that should be notified if the AppDomain shuts down. RegisterObject() requires an interface with a Stop() method that's fired and allows your code to respond to a shutdown request. Here's what the IRegisteredObject::Stop() method looks like on the launcher:public void Stop(bool immediate = false) { LogManager.Current.LogInfo("QueueManager Controller Stopped."); Controller.StopProcessing(); Controller.Dispose(); Thread.Sleep(1500); // give background threads some time HostingEnvironment.UnregisterObject(this); }Implementing IRegisterObject should help with reliability on AppDomain shutdowns. Thanks to Justin Van Patten for pointing this out to me on Twitter.RegisterObject() is not required but I would highly recommend implementing it on whatever object controls your background processing to all clean shutdowns when the AppDomain shuts down.Testing it outI'm still in the testing phase with this particular service to see if there are any side effects. But so far it doesn't look like it. With about 50 lines of code I was able to replace the Windows service startup to Web start up - everything else just worked as is. An honorable mention goes to SignalR 2.0's oWin hosting, because with the new oWin based hosting no code changes at all were required, merely a couple of configuration file settings and an assembly directive needed, to point at the SignalR startup class. Sweet!It also seems like SignalR is noticeably faster running inside of IIS compared to self-host. Startup feels faster because of the preload.Starting and Stopping the 'Service'Because the application is running as a Web Server, it's easy to have a Web interface for starting and stopping the services running inside of the service. For our queue manager the SignalR service and front monitoring app has a play and stop button for toggling the queue.If you want more administrative control and have it work more like a Windows Service you can also stop the application pool explicitly from the command line which would be equivalent to stopping and restarting a service.To start and stop from the command line you can use the IIS appCmd tool. To stop:> %windir%\system32\inetsrv\appcmd stop apppool /apppool.name:"Weblog"and to start> %windir%\system32\inetsrv\appcmd start apppool /apppool.name:"Weblog"Note that when you explicitly force the AppPool to stop running either in the UI (on the ApplicationPools page use Start/Stop) or via command line tools, the application pool will not auto-restart immediately. You have to manually start it back up.What's not to like?There are certainly a lot of benefits to running a background service in IIS, but… ASP.NET applications do have more overhead in terms of memory footprint and startup time is a little slower, but generally for server applications this is not a big deal. If the application is stable the service should fire up and stay running indefinitely. A lot of times this kind of service interface can simply be attached to an existing Web application, or if scalability requires be offloaded to its own Web server.Easier to work withBut the ultimate benefit here is that it's much easier to work with a Web app as opposed to a service. While developing I can simply turn off the auto-launch features and launch the service on demand through IIS simply by hitting a page on the site. If I want to shut down an IISRESET -stop will shut down the service easily enough. I can then attach a debugger anywhere I want and this works like any other ASP.NET application. Yes you end up on a background thread for debugging but Visual Studio handles that just fine and if you stay on a single thread this is no different than debugging any other code.SummaryUsing ASP.NET to run background service operations is probably not a super common scenario, but it probably should be something that is considered carefully when building services. Many applications have service like features and with the auto-start functionality of the Application Initialization module, it's easy to build this functionality into ASP.NET. Especially when combined with the notification features of SignalR it becomes very, very easy to create rich services that can also communicate their status easily to the outside world.Whether it's existing applications that need some background processing for scheduling related tasks, or whether you just create a separate site altogether just to host your service it's easy to do and you can leverage the same tool chain you're already using for other Web projects. If you have lots of service projects it's worth considering… give it some thought…© Rick Strahl, West Wind Technologies, 2005-2013Posted in ASP.NET  SignalR  IIS   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Binding Contents of a ListBox to Selected Item from Another Listbox w/JSF & Managed Beans

  - by nieltown

  Hi there! I currently have a JSF application that uses two listboxes. The first, say ListBox1, contains a list of manufacturers; each option comes from the database (via a method getManufacturers in a class called QueryUtil), is populated dynamically, and its value is an integer ID. This part works so far. My goal is to populate a second listbox, say ListBox2, with a list of products sold by the manufacturer. This list of products will come from the database as well (products are linked to a manufacturer via a foreign key relationship, via a method getProducts in my QueryUtil class). How do I go about doing this? Please bear in mind that I've been working with JSF for under 24 hours; I'm willing to accept the fact that I'm missing something very rudimentary. Again, I've been able to populate the list of manufacturers just fine; unfortunately, adding the Products component gives me java.lang.IllegalArgumentException: argument type mismatch faces-config.xml <managed-bean> <managed-bean-name>ProductsBean</managed-bean-name> <managed-bean-class>com.nieltown.ProductsBean</managed-bean-class> <managed-bean-scope>request</managed-bean-scope> <managed-property> <property-name>manufacturers</property-name> <property-class>java.util.ArrayList</property-class> <value>#{manufacturers}</value> </managed-property> <managed-property> <property-name>selectedManufacturer</property-name> <property-class>java.lang.Integer</property-name> <value>#{selectedManufacturer}</value> </managed-property> <managed-property> <property-name>products</property-name> <property-class>java.util.ArrayList</property-class> <value>#{products}</value> </managed-property> <managed-property> <property-name>selectedProduct</property-name> <property-class>java.lang.Integer</property-name> <value>#{selectedProducts}</value> <managed-property> </managed-bean> com.nieltown.ProductsBean public class ProductsBean { private List<SelectItem> manufacturers; private List<SelectItem> products; private Integer selectedManufacturer; private Integer selectedProduct; public ProductsBean() {} public Integer getSelectedManufacturer(){ return selectedManufacturer; } public void setSelectedManufacturer(Integer m){ selectedManufacturer = m; } public Integer getSelectedProduct(){ return selectedProduct; } public void setSelectedProduct(Integer p){ selectedProduct = p; } public List<SelectItem> getManufacturers(){ if(manufacturers == null){ SelectItem option; plans = new ArrayList<SelectItem>(); QueryUtil qu = new QueryUtil(); Map<Integer, String> manufacturersMap = qu.getManufacturers(); for(Map.Entry<Integer, String> entry : manufacturersMap.entrySet()){ option = new SelectItem(entry.getKey(),entry.getValue()); manufacturers.add(option); } } return manufacturers; } public void setManufacturers(List<SelectItem> l){ manufacturers = l; } public List<SelectItem> getProducts(){ if(products == null){ SelectItem option; products = new ArrayList<SelectItem>(); if(selectedPlan != null){ PMTQueryUtil pqu = new PMTQueryUtil(); Map<Integer, String> productsMap = pqu.getProducts(); for(Map.Entry<Integer, String> entry : productsMap.entrySet()){ option = new SelectItem(entry.getKey(),entry.getValue()); products.add(option); } } } return products; } public void setProducts(List<SelectItem> l){ products = l; } } JSP fragment <h:selectOneListbox id="manufacturerList" value="#{ProductsBean.selectedManufacturer}" size="10"> <f:selectItems value="#{ProductsBean.manufacturers}" /> </h:selectOneListbox> <h:selectOneListbox id="productList" value="#{PendingPlansBean.selectedProduct}" size="10"> <f:selectItems binding="#{ProductsBean.products}" /> </h:selectOneListbox>

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• Beware Sneaky Reads with Unique Indexes

  - by Paul White NZ

  A few days ago, Sandra Mueller (twitter | blog) asked a question using twitter’s #sqlhelp hash tag: “Might SQL Server retrieve (out-of-row) LOB data from a table, even if the column isn’t referenced in the query?” Leaving aside trivial cases (like selecting a computed column that does reference the LOB data), one might be tempted to say that no, SQL Server does not read data you haven’t asked for.  In general, that’s quite correct; however there are cases where SQL Server might sneakily retrieve a LOB column… Example Table Here’s a T-SQL script to create that table and populate it with 1,000 rows: CREATE TABLE dbo.LOBtest ( pk INTEGER IDENTITY NOT NULL, some_value INTEGER NULL, lob_data VARCHAR(MAX) NULL, another_column CHAR(5) NULL, CONSTRAINT [PK dbo.LOBtest pk] PRIMARY KEY CLUSTERED (pk ASC) ); GO DECLARE @Data VARCHAR(MAX); SET @Data = REPLICATE(CONVERT(VARCHAR(MAX), 'x'), 65540);   WITH Numbers (n) AS ( SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) FROM master.sys.columns C1, master.sys.columns C2 ) INSERT LOBtest WITH (TABLOCKX) ( some_value, lob_data ) SELECT TOP (1000) N.n, @Data FROM Numbers N WHERE N.n <= 1000; Test 1: A Simple Update Let’s run a query to subtract one from every value in the some_value column: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; As you might expect, modifying this integer column in 1,000 rows doesn’t take very long, or use many resources.  The STATITICS IO and TIME output shows a total of 9 logical reads, and 25ms elapsed time.  The query plan is also very simple: Looking at the Clustered Index Scan, we can see that SQL Server only retrieves the pk and some_value columns during the scan: The pk column is needed by the Clustered Index Update operator to uniquely identify the row that is being changed.  The some_value column is used by the Compute Scalar to calculate the new value.  (In case you are wondering what the Top operator is for, it is used to enforce SET ROWCOUNT). Test 2: Simple Update with an Index Now let’s create a nonclustered index keyed on the some_value column, with lob_data as an included column: CREATE NONCLUSTERED INDEX [IX dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest (some_value) INCLUDE ( lob_data ) WITH ( FILLFACTOR = 100, MAXDOP = 1, SORT_IN_TEMPDB = ON ); This is not a useful index for our simple update query; imagine that someone else created it for a different purpose.  Let’s run our update query again: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; We find that it now requires 4,014 logical reads and the elapsed query time has increased to around 100ms.  The extra logical reads (4 per row) are an expected consequence of maintaining the nonclustered index. The query plan is very similar to before (click to enlarge): The Clustered Index Update operator picks up the extra work of maintaining the nonclustered index. The new Compute Scalar operators detect whether the value in the some_value column has actually been changed by the update.  SQL Server may be able to skip maintaining the nonclustered index if the value hasn’t changed (see my previous post on non-updating updates for details).  Our simple query does change the value of some_data in every row, so this optimization doesn’t add any value in this specific case. The output list of columns from the Clustered Index Scan hasn’t changed from the one shown previously: SQL Server still just reads the pk and some_data columns.  Cool. Overall then, adding the nonclustered index hasn’t had any startling effects, and the LOB column data still isn’t being read from the table.  Let’s see what happens if we make the nonclustered index unique. Test 3: Simple Update with a Unique Index Here’s the script to create a new unique index, and drop the old one: CREATE UNIQUE NONCLUSTERED INDEX [UQ dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest (some_value) INCLUDE ( lob_data ) WITH ( FILLFACTOR = 100, MAXDOP = 1, SORT_IN_TEMPDB = ON ); GO DROP INDEX [IX dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest; Remember that SQL Server only enforces uniqueness on index keys (the some_data column).  The lob_data column is simply stored at the leaf-level of the non-clustered index.  With that in mind, we might expect this change to make very little difference.  Let’s see: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; Whoa!  Now look at the elapsed time and logical reads: Scan count 1, logical reads 2016, physical reads 0, read-ahead reads 0, lob logical reads 36015, lob physical reads 0, lob read-ahead reads 15992.   CPU time = 172 ms, elapsed time = 16172 ms. Even with all the data and index pages in memory, the query took over 16 seconds to update just 1,000 rows, performing over 52,000 LOB logical reads (nearly 16,000 of those using read-ahead). Why on earth is SQL Server reading LOB data in a query that only updates a single integer column? The Query Plan The query plan for test 3 looks a bit more complex than before: In fact, the bottom level is exactly the same as we saw with the non-unique index.  The top level has heaps of new stuff though, which I’ll come to in a moment. You might be expecting to find that the Clustered Index Scan is now reading the lob_data column (for some reason).  After all, we need to explain where all the LOB logical reads are coming from.  Sadly, when we look at the properties of the Clustered Index Scan, we see exactly the same as before: SQL Server is still only reading the pk and some_value columns – so what’s doing the LOB reads? Updates that Sneakily Read Data We have to go as far as the Clustered Index Update operator before we see LOB data in the output list: [Expr1020] is a bit flag added by an earlier Compute Scalar.  It is set true if the some_value column has not been changed (part of the non-updating updates optimization I mentioned earlier). The Clustered Index Update operator adds two new columns: the lob_data column, and some_value_OLD.  The some_value_OLD column, as the name suggests, is the pre-update value of the some_value column.  At this point, the clustered index has already been updated with the new value, but we haven’t touched the nonclustered index yet. An interesting observation here is that the Clustered Index Update operator can read a column into the data flow as part of its update operation.  SQL Server could have read the LOB data as part of the initial Clustered Index Scan, but that would mean carrying the data through all the operations that occur prior to the Clustered Index Update.  The server knows it will have to go back to the clustered index row to update it, so it delays reading the LOB data until then.  Sneaky! Why the LOB Data Is Needed This is all very interesting (I hope), but why is SQL Server reading the LOB data?  For that matter, why does it need to pass the pre-update value of the some_value column out of the Clustered Index Update? The answer relates to the top row of the query plan for test 3.  I’ll reproduce it here for convenience: Notice that this is a wide (per-index) update plan.  SQL Server used a narrow (per-row) update plan in test 2, where the Clustered Index Update took care of maintaining the nonclustered index too.  I’ll talk more about this difference shortly. The Split/Sort/Collapse combination is an optimization, which aims to make per-index update plans more efficient.  It does this by breaking each update into a delete/insert pair, reordering the operations, removing any redundant operations, and finally applying the net effect of all the changes to the nonclustered index. Imagine we had a unique index which currently holds three rows with the values 1, 2, and 3.  If we run a query that adds 1 to each row value, we would end up with values 2, 3, and 4.  The net effect of all the changes is the same as if we simply deleted the value 1, and added a new value 4. By applying net changes, SQL Server can also avoid false unique-key violations.  If we tried to immediately update the value 1 to a 2, it would conflict with the existing value 2 (which would soon be updated to 3 of course) and the query would fail.  You might argue that SQL Server could avoid the uniqueness violation by starting with the highest value (3) and working down.  That’s fine, but it’s not possible to generalize this logic to work with every possible update query. SQL Server has to use a wide update plan if it sees any risk of false uniqueness violations.  It’s worth noting that the logic SQL Server uses to detect whether these violations are possible has definite limits.  As a result, you will often receive a wide update plan, even when you can see that no violations are possible. Another benefit of this optimization is that it includes a sort on the index key as part of its work.  Processing the index changes in index key order promotes sequential I/O against the nonclustered index. A side-effect of all this is that the net changes might include one or more inserts.  In order to insert a new row in the index, SQL Server obviously needs all the columns – the key column and the included LOB column.  This is the reason SQL Server reads the LOB data as part of the Clustered Index Update. In addition, the some_value_OLD column is required by the Split operator (it turns updates into delete/insert pairs).  In order to generate the correct index key delete operation, it needs the old key value. The irony is that in this case the Split/Sort/Collapse optimization is anything but.  Reading all that LOB data is extremely expensive, so it is sad that the current version of SQL Server has no way to avoid it. Finally, for completeness, I should mention that the Filter operator is there to filter out the non-updating updates. Beating the Set-Based Update with a Cursor One situation where SQL Server can see that false unique-key violations aren’t possible is where it can guarantee that only one row is being updated.  Armed with this knowledge, we can write a cursor (or the WHILE-loop equivalent) that updates one row at a time, and so avoids reading the LOB data: SET NOCOUNT ON; SET STATISTICS XML, IO, TIME OFF;   DECLARE @PK INTEGER, @StartTime DATETIME; SET @StartTime = GETUTCDATE();   DECLARE curUpdate CURSOR LOCAL FORWARD_ONLY KEYSET SCROLL_LOCKS FOR SELECT L.pk FROM LOBtest L ORDER BY L.pk ASC;   OPEN curUpdate;   WHILE (1 = 1) BEGIN FETCH NEXT FROM curUpdate INTO @PK;   IF @@FETCH_STATUS = -1 BREAK; IF @@FETCH_STATUS = -2 CONTINUE;   UPDATE dbo.LOBtest SET some_value = some_value - 1 WHERE CURRENT OF curUpdate; END;   CLOSE curUpdate; DEALLOCATE curUpdate;   SELECT DATEDIFF(MILLISECOND, @StartTime, GETUTCDATE()); That completes the update in 1280 milliseconds (remember test 3 took over 16 seconds!) I used the WHERE CURRENT OF syntax there and a KEYSET cursor, just for the fun of it.  One could just as well use a WHERE clause that specified the primary key value instead. Clustered Indexes A clustered index is the ultimate index with included columns: all non-key columns are included columns in a clustered index.  Let’s re-create the test table and data with an updatable primary key, and without any non-clustered indexes: IF OBJECT_ID(N'dbo.LOBtest', N'U') IS NOT NULL DROP TABLE dbo.LOBtest; GO CREATE TABLE dbo.LOBtest ( pk INTEGER NOT NULL, some_value INTEGER NULL, lob_data VARCHAR(MAX) NULL, another_column CHAR(5) NULL, CONSTRAINT [PK dbo.LOBtest pk] PRIMARY KEY CLUSTERED (pk ASC) ); GO DECLARE @Data VARCHAR(MAX); SET @Data = REPLICATE(CONVERT(VARCHAR(MAX), 'x'), 65540);   WITH Numbers (n) AS ( SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) FROM master.sys.columns C1, master.sys.columns C2 ) INSERT LOBtest WITH (TABLOCKX) ( pk, some_value, lob_data ) SELECT TOP (1000) N.n, N.n, @Data FROM Numbers N WHERE N.n <= 1000; Now here’s a query to modify the cluster keys: UPDATE dbo.LOBtest SET pk = pk + 1; The query plan is: As you can see, the Split/Sort/Collapse optimization is present, and we also gain an Eager Table Spool, for Halloween protection.  In addition, SQL Server now has no choice but to read the LOB data in the Clustered Index Scan: The performance is not great, as you might expect (even though there is no non-clustered index to maintain): Table 'LOBtest'. Scan count 1, logical reads 2011, physical reads 0, read-ahead reads 0, lob logical reads 36015, lob physical reads 0, lob read-ahead reads 15992.   Table 'Worktable'. Scan count 1, logical reads 2040, physical reads 0, read-ahead reads 0, lob logical reads 34000, lob physical reads 0, lob read-ahead reads 8000.   SQL Server Execution Times: CPU time = 483 ms, elapsed time = 17884 ms. Notice how the LOB data is read twice: once from the Clustered Index Scan, and again from the work table in tempdb used by the Eager Spool. If you try the same test with a non-unique clustered index (rather than a primary key), you’ll get a much more efficient plan that just passes the cluster key (including uniqueifier) around (no LOB data or other non-key columns): A unique non-clustered index (on a heap) works well too: Both those queries complete in a few tens of milliseconds, with no LOB reads, and just a few thousand logical reads.  (In fact the heap is rather more efficient). There are lots more fun combinations to try that I don’t have space for here. Final Thoughts The behaviour shown in this post is not limited to LOB data by any means.  If the conditions are met, any unique index that has included columns can produce similar behaviour – something to bear in mind when adding large INCLUDE columns to achieve covering queries, perhaps. Paul White Email: [email protected] Twitter: @PaulWhiteNZ

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• Uploadify Minimum Image Width And Height

  - by Richard Knop

  So I am using the Uplodify plugin to allow users to upload multiple images at once. The problem is I need to set a minimum width and height for images. Let's say 150x150px is the smallest image users can upload. How can I set this limitation in the Uploadify plugin? When user tries to upload smaller picture, I would like to display some error message as well. Here is the PHP file that is called bu the plugin to upload images: <?php define('BASE_PATH', substr(dirname(dirname(__FILE__)), 0, -22)); // set the include path set_include_path(BASE_PATH . '/../library' . PATH_SEPARATOR . BASE_PATH . '/library' . PATH_SEPARATOR . get_include_path()); // autoload classes from the library function __autoload($class) { include str_replace('_', '/', $class) . '.php'; } $configuration = new Zend_Config_Ini(BASE_PATH . '/application' . '/configs/application.ini', 'development'); $dbAdapter = Zend_Db::factory($configuration->database); Zend_Db_Table_Abstract::setDefaultAdapter($dbAdapter); function _getTable($table) { include BASE_PATH . '/application/modules/default/models/' . $table . '.php'; return new $table(); } $albums = _getTable('Albums'); $media = _getTable('Media'); if (false === empty($_FILES)) { $tempFile = $_FILES['Filedata']['tmp_name']; $extension = end(explode('.', $_FILES['Filedata']['name'])); // insert temporary row into the database $data = array(); $data['type'] = 'photo'; $data['type2'] = 'public'; $data['status'] = 'temporary'; $data['user_id'] = $_REQUEST['user_id']; $paths = $media->add($data, $extension, $dbAdapter); // save the photo move_uploaded_file($tempFile, BASE_PATH . '/public/' . $paths[0]); // create a thumbnail include BASE_PATH . '/library/My/PHPThumbnailer/ThumbLib.inc.php'; $thumb = PhpThumbFactory::create(BASE_PATH . '/public/' . $paths[0]); $thumb->adaptiveResize(85, 85); $thumb->save(BASE_PATH . '/public/' . $paths[1]); // add watermark to the bottom right corner $pathToFullImage = BASE_PATH . '/public/' . $paths[0]; $size = getimagesize($pathToFullImage); switch ($extension) { case 'gif': $im = imagecreatefromgif($pathToFullImage); break; case 'jpg': $im = imagecreatefromjpeg($pathToFullImage); break; case 'png': $im = imagecreatefrompng($pathToFullImage); break; } if (false !== $im) { $white = imagecolorallocate($im, 255, 255, 255); $font = BASE_PATH . '/public/fonts/arial.ttf'; imagefttext($im, 13, // font size 0, // angle $size[0] - 132, // x axis (top left is [0, 0]) $size[1] - 13, // y axis $white, $font, 'HunnyHive.com'); switch ($extension) { case 'gif': imagegif($im, $pathToFullImage); break; case 'jpg': imagejpeg($im, $pathToFullImage, 100); break; case 'png': imagepng($im, $pathToFullImage, 0); break; } imagedestroy($im); } echo "1"; } And here's the javascript: $(document).ready(function() { $('#photo').uploadify({ 'uploader' : '/flash-uploader/scripts/uploadify.swf', 'script' : '/flash-uploader/scripts/upload-public-photo.php', 'cancelImg' : '/flash-uploader/cancel.png', 'scriptData' : {'user_id' : 'USER_ID'}, 'queueID' : 'fileQueue', 'auto' : true, 'multi' : true, 'sizeLimit' : 2097152, 'fileExt' : '*.jpg;*.jpeg;*.gif;*.png', 'wmode' : 'transparent', 'onComplete' : function() { $.get('/my-account/temporary-public-photos', function(data) { $('#temporaryPhotos').html(data); }); } }); $('#upload_public_photo').hover(function() { var titles = '{'; $('.title').each(function() { var title = $(this).val(); if ('Title...' != title) { var id = $(this).attr('name'); id = id.substr(5); title = jQuery.trim(title); if (titles.length > 1) { titles += ','; } titles += '"' + id + '"' + ':"' + title + '"'; } }); titles += '}'; $('#titles').val(titles); }); }); Now bear in mind that I know how to check images dimensions in the PHP file. But I'm not sure how to modify the javascript so it won't upload images with very small dimensions.

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• C++ Mutexes and STL Lists Across Subclasses

  - by Genesis

  I am currently writing a multi-threaded C++ server using Poco and am now at the point where I need to be keeping information on which users are connected, how many connections each of them have, and given it is a proxy server, where each of those connections are proxying through to. For this purpose I have created a ServerStats class which holds an STL list of ServerUser objects. The ServerStats class includes functions which can add and remove objects from the list as well as find a user in the list an return a pointer to them so I can access member functions within any given ServerUser object in the list. The ServerUser class contains an STL list of ServerConnection objects and much like the ServerStats class it contains functions to add, remove and find elements within this list. Now all of the above is working but I am now trying to make it threadsafe. I have defined a Poco::FastMutex within the ServerStats class and can lock/unlock this in the appropriate places so that STL containers are not modified at the same time as being searched for example. I am however having an issue setting up mutexes within the ServerUser class and am getting the following compiler error: /root/poco/Foundation/include/Poco/Mutex.h: In copy constructor âServerUser::ServerUser(const ServerUser&)â: src/SocksServer.cpp:185: instantiated from âvoid __gnu_cxx::new_allocator<_Tp::construct(_Tp*, const _Tp&) [with _Tp = ServerUser]â /usr/include/c++/4.4/bits/stl_list.h:464: instantiated from âstd::_List_node<_Tp* std::list<_Tp, _Alloc::_M_create_node(const _Tp&) [with _Tp = ServerUser, _Alloc = std::allocator]â /usr/include/c++/4.4/bits/stl_list.h:1407: instantiated from âvoid std::list<_Tp, _Alloc::_M_insert(std::_List_iterator<_Tp, const _Tp&) [with _Tp = ServerUser, _Alloc = std::allocator]â /usr/include/c++/4.4/bits/stl_list.h:920: instantiated from âvoid std::list<_Tp, _Alloc::push_back(const _Tp&) [with _Tp = ServerUser, _Alloc = std::allocator]â src/SocksServer.cpp:301: instantiated from here /root/poco/Foundation/include/Poco/Mutex.h:164: error: âPoco::FastMutex::FastMutex(const Poco::FastMutex&)â is private src/SocksServer.cpp:185: error: within this context In file included from /usr/include/c++/4.4/x86_64-linux-gnu/bits/c++allocator.h:34, from /usr/include/c++/4.4/bits/allocator.h:48, from /usr/include/c++/4.4/string:43, from /root/poco/Foundation/include/Poco/Bugcheck.h:44, from /root/poco/Foundation/include/Poco/Foundation.h:147, from /root/poco/Net/include/Poco/Net/Net.h:45, from /root/poco/Net/include/Poco/Net/TCPServerParams.h:43, from src/SocksServer.cpp:1: /usr/include/c++/4.4/ext/new_allocator.h: In member function âvoid __gnu_cxx::new_allocator<_Tp::construct(_Tp*, const _Tp&) [with _Tp = ServerUser]â: /usr/include/c++/4.4/ext/new_allocator.h:105: note: synthesized method âServerUser::ServerUser(const ServerUser&)â first required here src/SocksServer.cpp: At global scope: src/SocksServer.cpp:118: warning: âstd::string getWord(std::string)â defined but not used make: * [/root/poco/SocksServer/obj/Linux/x86_64/debug_shared/SocksServer.o] Error 1 The code for the ServerStats, ServerUser and ServerConnection classes is below: class ServerConnection { public: bool continue_connection; int bytes_in; int bytes_out; string source_address; string destination_address; ServerConnection() { continue_connection = true; } ~ServerConnection() { } }; class ServerUser { public: string username; int connection_count; string client_ip; ServerUser() { } ~ServerUser() { } ServerConnection* addConnection(string source_address, string destination_address) { //FastMutex::ScopedLock lock(_connection_mutex); ServerConnection connection; connection.source_address = source_address; connection.destination_address = destination_address; client_ip = getWord(source_address, ":"); _connections.push_back(connection); connection_count++; return &_connections.back(); } void removeConnection(string source_address) { //FastMutex::ScopedLock lock(_connection_mutex); for(list<ServerConnection>::iterator it = _connections.begin(); it != _connections.end(); it++) { if(it->source_address == source_address) { it = _connections.erase(it); connection_count--; } } } void disconnect() { //FastMutex::ScopedLock lock(_connection_mutex); for(list<ServerConnection>::iterator it = _connections.begin(); it != _connections.end(); it++) { it->continue_connection = false; } } list<ServerConnection>* getConnections() { return &_connections; } private: list<ServerConnection> _connections; //UNCOMMENTING THIS LINE BREAKS IT: //mutable FastMutex _connection_mutex; }; class ServerStats { public: int current_users; ServerStats() { current_users = 0; } ~ServerStats() { } ServerUser* addUser(string username) { FastMutex::ScopedLock lock(_user_mutex); for(list<ServerUser>::iterator it = _users.begin(); it != _users.end(); it++) { if(it->username == username) { return &(*it); } } ServerUser newUser; newUser.username = username; _users.push_back(newUser); current_users++; return &_users.back(); } void removeUser(string username) { FastMutex::ScopedLock lock(_user_mutex); for(list<ServerUser>::iterator it = _users.begin(); it != _users.end(); it++) { if(it->username == username) { _users.erase(it); current_users--; break; } } } ServerUser* getUser(string username) { FastMutex::ScopedLock lock(_user_mutex); for(list<ServerUser>::iterator it = _users.begin(); it != _users.end(); it++) { if(it->username == username) { return &(*it); } } return NULL; } private: list<ServerUser> _users; mutable FastMutex _user_mutex; }; Now I have never used C++ for a project of this size or mutexes for that matter so go easy please :) Firstly, can anyone tell me why the above is causing a compiler error? Secondly, can anyone suggest a better way of storing the information I require? Bear in mind that I need to update this info whenever connections come or go and it needs to be global to the whole server.

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• Adding attachments to HumanTasks *beforehand*

  - by ccasares

  For an demo I'm preparing along with a partner, we need to add some attachments to a HumanTask beforehand, that is, the attachment must be associated already to the Task by the time the user opens its Form. How to achieve this?, indeed it's quite simple and just a matter of some mappings to the Task's input execData structure. Oracle BPM supports "default" attachments (which use BPM tables) or UCM-based ones. The way to insert attachments for both methods is pretty similar. With default attachments When using default attachments, first we need to have the attachment payload as part of the BPM process, that is, must be contained in a variable. Normally the attachment content is binary, so we'll need first to convert it to a base64-string (not covered on this blog entry). What we need to do is just to map the following execData parameters as part of the input of the HumanTask: execData.attachment[n].content            <-- the base64 payload data execData.attachment[n].mimeType           <-- depends on your attachment                                               (e.g.: "application/pdf") execData.attachment[n].name               <-- attachment name (just the name you want to                                               use. No need to be the original filename) execData.attachment[n].attachmentScope    <-- BPM or TASK (depending on your needs) execData.attachment[n].storageType        <-- TASK execData.attachment[n].doesBelongToParent <-- false (not sure if this one is really                                               needed, but it definitely doesn't hurt) execData.attachment[n].updatedBy          <-- username who is attaching it execData.attachment[n].updatedDate        <-- dateTime of when this attachment is                                               attached  Bear in mind that the attachment structure is a repetitive one. So if you need to add more than one attachment, you'll need to use XSLT mapping. If not, the Assign mapper automatically adds [1] for the iteration.  With UCM-based attachments With UCM-based attachments, the procedure is basically the same. We'll need to map some extra fields and not to map others. The tricky part with UCM-based attachments is what we need to know beforehand about the attachment itself. Of course, we don't need to have the payload, but a couple of information from the attachment that must be checked in already in UCM. First, let's see the mappings: execData.attachment[n].mimeType           <-- Document's dFormat attribute (1) execData.attachment[n].name               <-- attachment name (just the name you want to                                               use. No need to be the original filename) execData.attachment[n].attachmentScope    <-- BPM or TASK (depending on your needs) execData.attachment[n].storageType        <-- UCM execData.attachment[n].doesBelongToParent <-- false (not sure if this one is really                                               needed, but it definitely doesn't hurt) execData.attachment[n].updatedBy          <-- username who is attaching it execData.attachment[n].updatedDate        <-- dateTime of when this attachment is                                               attached  execData.attachment[n].uri                <-- "ecm://<dID>" where dID is document's dID                                      attribute (2) execData.attachment[n].ucmDocType         <-- Document's dDocType attribute (3) execData.attachment[n].securityGroup      <-- Document's dSecurityGroup attribute (4) execData.attachment[n].revision           <-- Document's dRevisionID attribute (5) execData.attachment[n].ucmMetadataItem[1].name  <-- "DocUrl" execData.attachment[n].ucmMetadataItem[1].type  <-- STRING execData.attachment[n].ucmMetadataItem[1].value <-- Document's url attribute (6)  Where to get those (n) fields? In my case I get those from a Search call to UCM (not covered on this blog entry) As I mentioned above, we must know which UCM document we're going to attach. We may know its ID, its name... whatever we need to uniquely identify it calling the IDC Search method. This method returns ALL the info we need to attach the different fields labeled with a number above.  The only tricky one is (6). UCM Search service returns the url attribute as a context-root without hostname:port. E.g.: /cs/groups/public/documents/document/dgvs/mdaw/~edisp/ccasareswcptel000239.pdf However we do need to include the full qualified URL when mapping (6). Where to get the http://<hostname>:<port> value? Honestly, I have no clue. What I use to do is to use a BPM property that can always be modified at runtime if needed. There are some other fields that might be needed in the execData.attachment structure, like account (if UCM's is using Accounts). But for demos I've never needed to use them, so I'm not sure whether it's necessary or not. Feel free to add some comments to this entry if you know it ;-)  That's all folks. Should you need help with the UCM Search service, let me know and I can write a quick entry on that topic.

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