portable applications - Page 587

Using Qt signals/slots instead of a worker thread

- by Rob

I am using Qt and wish to write a class that will perform some network-type operations, similar to FTP/HTTP. The class needs to connect to lots of machines, one after the other but I need the applications UI to stay (relatively) responsive during this process, so the user can cancel the operation, exit the application, etc. My first thought was to use a separate thread for network stuff but the built-in Qt FTP/HTTP (and other) classes apparently avoid using threads and instead rely on signals and slots. So, I'd like to do something similar and was hoping I could do something like this: class Foo : public QObject { Q_OBJECT public: void start(); signals: void next(); private slots: void nextJob(); }; void Foo::start() { ... connect(this, SIGNAL(next()), this, SLOT(nextJob())); emit next(); } void Foo::nextJob() { // Process next 'chunk' if (workLeftToDo) { emit next(); } } void Bar::StartOperation() { Foo* foo = new Foo; foo->start(); } However, this doesn't work and UI freezes until all operations have completed. I was hoping that emitting signals wouldn't actually call the slots immediately but would somehow be queued up by Qt, allowing the main UI to still operate. So what do I need to do in order to make this work? How does Qt achieve this with the multitude of built-in classes that appear to perform lengthy tasks on a single thread?

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Debugging an unresponsive iPhone UI

- by buggles

I have an application that needs to update its display every minute or so. To achieve this I was using performSelector:withObject:afterDelay, calling the selector that most of the time just changes some text in a label based on a very simple (and quick) calculation. [self performSelector:@selector(updateDisplay) withObject:nil afterDelay:60]; Occasionally during an update, I have to go off and get some data from the web, and so I do that in another thread using detachNewThreadSelector. That all worked and the "performSelector after Delay" call completes in a tiny fraction of a second, and only runs once a minute. Despite this, and despite running fine on the simulator, the single button in the app is largely unresponsive, not responding to multiple stabs. So, I had assumed peformSelector:afterDelay would not block, but I'm now wondering if it is blocking in some way? I even tried NOT doing the web-look-up incase this was somehow still impacting the responsiveness. No joy. [NSThread detachNewThreadSelector:@selector(updateFromURL) toTarget:self withObject:nil]; I then pushed it through shark to see if I could see anything obvious. From here I can see the web-lookup is the only thing taking any time, but it is only being done every couple of minutes, and then clearly not running on the main thread. The app itself is consuming a tiny fraction of 1% of the CPU (0.0000034%) over 20 minutes, so it just must be a blocking issue. So, am I missing something about performSelector:afterDelay? What other common newbie mistakes might I be making. If it helps, although I've been developing applications for over 20 years, the previous 10 have been largely Java. Perhaps I have a Java assumption loaded :-) Essentially I have assumed the main thread is like the EDT (only do UI stuff on it, but keep everything else off it).

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What should a developer know before building a public web site?

- by Joel Coehoorn

What things should a programmer implementing the technical details of a web site address before making the site public? If Jeff Atwood can forget about HttpOnly cookies, sitemaps, and cross-site request forgeries all in the same site, what important thing could I be forgetting as well? I'm thinking about this from a web developer's perspective, such that someone else is creating the actual design and content for the site. So while usability and content may be more important than the platform, you the programmer have little say in that. What you do need to worry about is that your implementation of the platform is stable, performs well, is secure, and meets any other business goals (like not cost too much, take too long to build, and rank as well with Google as the content supports). Think of this from the perspective of a developer who's done some work for intranet-type applications in a fairly trusted environment, and is about to have his first shot and putting out a potentially popular site for the entire big bad world wide web. Also: I'm looking for something more specific than just a vague "web standards" response. I mean, HTML, JavaScript, and CSS over HTTP are pretty much a given, especially when I've already specified that you're a professional web developer. So going beyond that, Which standards? In what circumstances, and why? Provide a link to the standard's specification. This question is community wiki, so please feel free to edit that answer to add links to good articles that will help explain or teach each particular point.

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Problem consuming Exchange Web Service 2010 with jax-ws metro

- by Johan Karlberg

I am trying to consume the Exchange 2010 Web Service interface using JAX-WS. I'm using JAX-WS 2.2 RI (Metro 2.0). 2.1 exhibited the same problem. I am running into trouble with Exchange, which returns "HTTP/1.1 415 Cannot process the message because the content type 'text/xml;charset=utf-8' was not the expected type 'text/xml; charset=utf-8'." as a reponse (2.1 quoted the charset value, otherwise same response). Apparently I need to dictate the exact Content-type header for Exchange to be happy. Is there a way for me to do this without forcing me to manually rebuild the dependency? I currently rely on published maven artifacts, and would like to continue doing this if at all possible. The consuming process is a regular J2SE app, with no containers in sight. I have control of the application and can add pretty much anything required to the applications scope, but can not add out-of-process items like proxy servers. The client classes were generated from local WSDL, but the charset specification is derived from constants declared in the jaxws RI implementation, not the generated code. The resulting HTTP transport is thus handled by the standard http/https client from Sun JRE5 or JRE6.

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trying to use mod_proxy with httpd and tomcat

- by techsjs2012

I been trying to use mod_proxy with httpd and tomcat... I have on VirtualBox running Scientific Linux which has httpd and tomcat 6 on it.. I made two nodes of tomcat6. I followed this guide like 10 times and still cant get the 2nd node of tomcat working.. http://www.richardnichols.net/2010/08/5-minute-guide-clustering-apache-tomcat/ Here is the lines from my http.conf file <Proxy balancer://testcluster stickysession=JSESSIONID> BalancerMember ajp://127.0.0.1:8009 min=10 max=100 route=node1 loadfactor=1 BalancerMember ajp://127.0.0.1:8109 min=10 max=100 route=node2 loadfactor=1 </Proxy> ProxyPass /examples balancer://testcluster/examples <Location /balancer-manager> SetHandler balancer-manager AuthType Basic AuthName "Balancer Manager" AuthUserFile "/etc/httpd/conf/.htpasswd" Require valid-user </Location> Now here is my server.xml from node1 <?xml version='1.0' encoding='utf-8'?>   <Server port="8005" shutdown="SHUTDOWN">  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />  <Listener className="org.apache.catalina.core.JasperListener" />  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />  <GlobalNamingResources>  <Resource name="UserDatabase" auth="Container" type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" pathname="conf/tomcat-users.xml" /> </GlobalNamingResources>  <Service name="Catalina">         <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />   <Engine name="Catalina" defaultHost="localhost" jvmRoute="node1">      <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/>  <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true" xmlValidation="false" xmlNamespaceAware="false">     </Host> </Engine> </Service> </Server> now here is the server.xml file from node2 <?xml version='1.0' encoding='utf-8'?>   <Server port="8105" shutdown="SHUTDOWN">  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />  <Listener className="org.apache.catalina.core.JasperListener" />  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />  <GlobalNamingResources>  <Resource name="UserDatabase" auth="Container" type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" pathname="conf/tomcat-users.xml" /> </GlobalNamingResources>  <Service name="Catalina">         <Connector port="8109" protocol="AJP/1.3" redirectPort="8443" />   <Engine name="Catalina" defaultHost="localhost" jvmRoute="node2">      <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/>  <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true" xmlValidation="false" xmlNamespaceAware="false">     </Host> </Engine> </Service> </Server> I dont know what it is. but I been trying for days

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How can I open VLC via browser with PHP (Mac OS X)

- by Damiqib

I'm trying to open VLC via browser and make it instantly play the given video file on Mac OS X. This runs on my local server and is only meant to run locally - therefore I already run apache (MAMP) with my username and with group "staff" (defined in httpd.conf). YES - I do know that VLC has http interface - however that is not what I need, so do not suggest that... My current system works without any problems when I run it via Terminal: php /var/www/Movies/index.php - This leads to VLC opening and video starts playing fullscreen like intented. Problems start when I run the same PHP-page with browser. Then the VLC-process starts, but there's no GUI for it, video file won't start playing and the VLC-process takes nearly 100% of CPU. Both; terminal and browser started VLC-processes run with the same user (mine) Both have "Parent process" bash VLC-process begun with Terminal has empty "Process group" (only process id-number) and browser started has "httpd" + (id-number) VLC-process started via browser makes 1000-times more "Mach System Calls" than it's Terminal-started counterpart. Could anyone give me any pointers on how to get this thing working? index.php # $j is a file path to the videofile and is defined before exec('/var/www/Movies/vlc.sh "' . $j . '" > /dev/null 2>&1 & echo $!;'); # If I do this in the given PHP-page it tells me that apache is running # with my username and with the group "staff" like it should be... exec('whoamI'); vlc.sh #!/bin/bash # Activate VLC in 5 seconds to make it the front-most window (sleep 5; open -a VLC) & # Open video file /Applications/VLC.app/Contents/MacOS/VLC --quiet --fullscreen "$1"

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Performance of java on different hardware?

- by tangens

In another SO question I asked why my java programs run faster on AMD than on Intel machines. But it seems that I'm the only one who has observed this. Now I would like to invite you to share the numbers of your local java performance with the SO community. I observed a big performance difference when watching the startup of JBoss on different hardware, so I set this program as the base for this comparison. For participation please download JBoss 5.1.0.GA and run: jboss-5.1.0.GA/bin/run.sh (or run.bat) This starts a standard configuration of JBoss without any extra applications. Then look for the last line of the start procedure which looks like this: [ServerImpl] JBoss (Microcontainer) [5.1.0.GA (build: SVNTag=JBoss_5_1_0_GA date=200905221634)] Started in 25s:264ms Please repeat this procedure until the printed time is somewhat stable and post this line together with some comments on your hardware (I used cpu-z to get the infos) and operating system like this: java version: 1.6.0_13 OS: Windows XP Board: ASUS M4A78T-E Processor: AMD Phenom II X3 720, 2.8 GHz RAM: 2*2 GB DDR3 (labeled 1333 MHz) GPU: NVIDIA GeForce 9400 GT disc: Seagate 1.5 TB (ST31500341AS) Use your votes to bring the fastest configuration to the top. I'm very curious about the results. EDIT: Up to now only a few members have shared their results. I'd really be interested in the results obtained with some other architectures. If someone works with a MAC (desktop) or runs an Intel i7 with less than 3 GHz, please once start JBoss and share your results. It will only take a few minutes.

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javascript table sorting/paging (client-side). How big is too big?

- by Aheho

I'm using a jQuery plugin called Tablesorter to do client-side sorting of a log table in one of my applications. I am also making use of the tablepager add-in. I really like the responsiveness that client-side sorting and paging brings to the party. I also like how you don't have to hit the web server or database repeatedly. However I can see that, in time, the log I'm displaying could grow quite large. I'm sure there comes a point where client-side paging and sorting is going to be impractical. What point will this technique begin to collapse under it's own weight? 500 records? 2000 records? 10,000 records? EDIT: In nutshell, what criteria would you use to determine if you are going to use client-side sorting/paging as opposed to server-side paging? Does the size of expected result set factor into your decision? Where is the tipping point?

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Authenticated WCF: Getting the Current Security Context

- by bradhe

I have the following scenario: I have various user's data stored in my database. This data was entered via a web app. We'd like to expose this data back to the user over a web service so that they can integrate their data with their applications. We would also like to expose some business logic over these services. As such we do not want to use OData. This is a multi-tenant application so I only want to expose their data back to them and not other users. Likewise, the business logic we expose should be relative to the authenticated user. I would like let the user use an OASIS scheme to authenticate with the web service -- WCF already allows for this out of the box as far as I understand -- or perhaps we can issue them certificates to authenticate with. That bit hasn't really been worked out yet. Here is a bit of pseudo-code of how I envision this would work within the service: function GetUsersData(id) var user := Lookup User based on Username from Auth Context var data := Get Data From Repository based on "user" return data end function For the business logic scenario I think it would look something like this: function PerformBusinessLogic(someData) var user := Lookup User based on Username from Auth Context var returnValue := Perform some logic based on supplied data return returnValue end function The hard bit here is getting the current username (or cert info in the cert scenario) that the user authenticated with! Does WCF even enable this scenario? If not would WSE3 enable this? Thanks,

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Regressing panel data in SAS.

- by John

Hey Guys, thanks to your help I succesfully managed all my databases! I am now looking at a panel data set on which I have to regress. Since I only started my Phd this semester together with the econometrics courses I am still new to many statistic applications and regression methods. I want to do a simple regression as in Y = x1 x2 x3 etc, now I already browsed through some literature and found that for panel data it's common to do a fixed effects regression. Also, my Y variable only has positive values so I was thinking in the direction of a Tobit model? I'm doing some research concerning the coverage of analysts in the financial business. My independent variable is the coverage of analysts on a certain firm, so per observation i have 1 analyst and 1 firm, together with different characteristics(market cap and betas etc) of the firm. All this data is monthly. As coverage cannot become negative (only 0) I was thinking of a Tobit model? Do you guys have any ideas what would be a good regression method? Or have some good sources (e books, written books, through university I have access to almost anything concerning my field of work) of information (cause I do have to learn these things for future research)? Thanks!

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Problem with relative path to image in XAML?

- by Giri

I am trying to reference a PNG file in my applications working directory through XAML with the following: <Image Name="contactImage"> <Image.Source> <BitmapImage UriSource="/Images/contact.png"> </Image.Source> </Image> Now in my code-behind I try to get the height of the image with contactImage.Source.Height This fails with System.IOException - cannot locate resource 'images/contact.png'. If I use something like PngBitmapDecoder p = new PngBitmapDecoder(new Uri("./Images/contact.png"), UriKind.Relative, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default); Everything is happy. How can I reference an image in xaml to a path relative to the working deirectory of the app. BTW- this is being run on a remote machine (if that makes a difference). I have tried "./Images/contact.png" and ".\Images\contact.png" and several other combinations of back/forward slashes and dots. Here is the primary difference- Any time the file is referenced in XAML, it shows up as pack://aplication:,,, blah blah blah when I use the PngBitmapDecoder, it shows up correctly as "./Images/contact.png". How do I reference the image file in XAML and get it show a source as "./Images/contact.png" instead of a pack://application,,,blah blah blah?

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Replacing .NET WebBrowser control with a better browser, like Chrome?

- by Sylverdrag

Is there any relatively easy way to insert a modern browser into a .NET application? As far as I understand, the WebBrowser control is a wrapper for IE, which wouldn't be a problem except that it looks like it is a very old version of IE, with all that entails in terms of CSS screw-ups, potential security risks (if the rendering engine wasn't patched, can I really expect the zillion buffer overflow problems to be fixed?), and other issues. I am using Visual Studio C# (express edition - does it make any difference here?) I would like to integrate a good web browser in my applications. In some, I just use it to handle the user registration process, interface with some of my website's features and other things of that order, but I have another application in mind that will require more err... control. I need: A browser that can integrate inside a window of my application (not a separate window) A good support for CSS, js and other web technologies, on par with any modern browser Basic browser functions like "navigate", "back", "reload"... Liberal access to the page code and output. I was thinking about Chrome, since it comes under the BSD license, but I would be just as happy with a recent version of IE. As much as possible, I would like to keep things simple. The best would be if one could patch the existing WebBrowser control, which does already about 70% of what I need, but I don't think that's possible. I have found an activeX control for Mozilla (http://www.iol.ie/~locka/mozilla/control.htm) but it looks like it's an old version, so it's not necessarily an improvement. I am open to suggestions

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Configure Windows firewall to prevent an application from listening on a specific port [closed]

- by U-D13

The issue: there are many applications struggling to listen on port 80 (Skype, Teamviewer et al.), and to many of them that even is not essential (in the sense that you can have a httpd running and blocking the http port, and the other application won't even squeak about being unable to open the port). What makes things worse, some of the apps are... Well, I suppose, that it's okay that the mentally impaired are being integrated in the society by giving them a job to do, but... Programming requires some intellectual effort, in my humble opinion... What I mean is that there is no way to configure the app not to use specific ports (that's what you get for using proprietary software) - you can either add it to windows firewall exceptions (and succumb to undesired port opening behavior) or not (and risk losing most - if not all - of the functionality). Technically, it is not impossible for the firewall to deny an application opening an incoming port even if the application is in the exception list. And if this functionality is built into the Windows firewall somewhere, there should be a way to activate it. So, what I want to know is: whether there exists such an option, and if it does how to activate it.

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How to configure oracle instantclient for mono?

- by funwithcoding

Mono is really awesome. Some of our applications worked in linux out of the box even without recompiling the binary. However I am having tough time to configure oracle instantclient to use it with mono. I installed instantclient on a CentOS VM(by installing instantclient rpm) but however I did not find TNSNAMES.ORA anywhere. I searched for oracle and I found the following path contains the oracle libraries. [root@bagvapp rupert]# ll /usr/lib/oracle/11.2/client/lib/ total 143280 -rw-r--r-- 1 root root 7456 Aug 14 2009 cobsqlintf.o -rw-r--r-- 1 root root 342 Aug 14 2009 glogin.sql lrwxrwxrwx 1 root root 17 Mar 9 06:52 libclntsh.so -> libclntsh.so.11.1 -rw-r--r-- 1 root root 40088477 Aug 14 2009 libclntsh.so.11.1 -rw-r--r-- 1 root root 6986848 Aug 14 2009 libnnz11.so lrwxrwxrwx 1 root root 15 Mar 9 06:52 libocci.so -> libocci.so.11.1 -rw-r--r-- 1 root root 1879549 Aug 14 2009 libocci.so.11.1 -rw-r--r-- 1 root root 89377610 Aug 14 2009 libociei.so -rw-r--r-- 1 root root 152304 Aug 14 2009 libocijdbc11.so -rw-r--r-- 1 root root 1501651 Aug 14 2009 libsqlplusic.so -rw-r--r-- 1 root root 1218075 Aug 14 2009 libsqlplus.so -rw-r--r-- 1 root root 777979 Aug 14 2009 libsqora.so.11.1 -rw-r--r-- 1 root root 1996228 Aug 14 2009 ojdbc5.jar -rw-r--r-- 1 root root 2111220 Aug 14 2009 ojdbc6.jar -rw-r--r-- 1 root root 298388 Aug 14 2009 ottclasses.zip drwxr-xr-x 3 root root 4096 Mar 9 06:52 precomp -rw-r--r-- 1 root root 37807 Aug 14 2009 xstreams.jar no TNSPING available, no TNSNAMES.ORA, Now how to configure the mono to use this as the oracle client? and how to specify oracle database in app.config connection string section? Though mono is a powerful framework, seems like it is having problems like linux does, all the documentation is only available in mailing lists and whatever is available on official site is either outdated or not clear for normal user. Hope things will change soon and Mono will THE programming framework for linux.

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Optimize Use of Ramdisk for Eclipse Development

- by Eric J.

We're developing Java/SpringSource applications with Eclipse on 32-bit Vista machines with 4GB RAM. The OS exposes roughly 3.3GB of RAM due to reservations for hardware etc. in the virtual address space. I came across several Ramdisk drivers that can create a virtual disk from the OS-hidden RAM and am looking for suggestions how best to use the 740MB virtual disk to speed development in our environment. The slowest part of development for us is compiling as well as launching SpringSource dm Server. One option is to configure Vista to swap to the Ramdisk. That works, and noticeably speeds up development in low memory situations. However, the 3.3GB available to the OS is often sufficient and there are many situations where we do not use the swap file(s) much. Another option is to use the Ramdisk as a location for temporary files. Using the Vista mklink command, I created a hard link from where the SpringSource dm Server's work area normally resides to the Ramdisk. That significantly improves server startup times but does nothing for compile times. There are roughly 500MB still free on the Ramdisk when the work directory is fully utilized, so room for plenty more. What other files/directories might be candidates to place on the Ramdisk? Eclipse-related files? (Parts of) the JDK? Is there a free/open source tool for Vista that will show me which files are used most frequently during a period of time to reduce the guesswork?

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GridView: How can I get rid of extra space from my GirdView object?

- by Lajos Arpad

Hello, I'm writing an application for Android phones for Human vs. Human chess play over the internet. I was looking at some tutorials, to learn how to develop Android applications and found a very nice example of making galleries (it was a GridView usage example for making a gallery about dogs) and the idea came to draw the chess table using a GridView, because the example project also handled the point & click event and I intended to use the same event in the same way, but for a different purpose. The game works well (currently it's a hotseat version), however, I'm really frustrated by the fact that whenever I rotate the screen of the phone, my GridView gets hysterical and puts some empty space in my chess table between the columns. I realized that the cause of this is that the GridView's width is the same as its parent's and the GridView tries to fill its parent in with, but there should (and probably is) be a simple solution to get rid of this problem. However, after a full day of researching, I haven't found any clue to help me to make a perfect drawing about my chess table without a negative side effect in functionality. The chess table looks fine if the phone is in Portrait mode, but in Landscape mode it's far from nice. This is how I can decide whether we are in Portrait or Landscape mode: ((((MainActivity)mContext).getWindow().getWindowManager().getDefaultDisplay().getWidth()) < ((MainActivity)mContext).getWindow().getWindowManager().getDefaultDisplay().getHeight()) In the main.xml file the GridView is defined in the following way: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <GridView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/gridview" android:layout_width="wrap_content" android:layout_height="wrap_content" android:numColumns="8" android:verticalSpacing="0dp" android:horizontalSpacing="0dp" android:stretchMode="columnWidth" android:gravity="center" > </GridView> ... </LinearLayout> I appreciate any help with the problem and thank you for reading this.

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Deployments and TFS, general questions

- by Velika

SOX requires that we have a separate group deploy our ASP.NET web to production. Currently, that group has access to our current code repository in VSS and uses VSS to deploy code that has been checked into VSS. How are deployments typically done for web applications? As a developer, I have used the Deploy function in Visual Studio to deploy code to a network share which corresponds to a IS virtual folder, but I don't think we can expect that the deployment group will be purchasing a copy of Visual Studio just to do deployments. We could check the code into TFS, but what is the minimum software that that group would need to perform the deployment? Would a Team Explorer Client Access suffice? I am aware that Team System has functionality to automate the building of an application. Do people typically deploy to Production by copying aspx and dlls files from the QA environment to production or do you normally deploy from TFS or even VS directly? It seems to me that the preferred approach would be to deploy from the QA environment, since that is the environment that must have been approved for release or that those files should be checked into TFS and the deployed from TFS, assuming you can deploy from TFS. What confuses me is whether bin (binary) files that are local to the project-do they go into TFS? Is so, doesn't this create problems for other developers in that only 1 developers-the one with the binary checked - can actually debug because debugging requires write access to the binaries? Does this mean that the binaries shouldn't be checked into TFS? But eventually, if you deploy from TFS, the binaries HAVE to be added to TFS. Are they added as a separate (compiled) application node? If so,m this sounds real ugly. I would assume not. How does one ensure that the binaries match the source code that we mark with a particular version number? Obviously, I'm clueless. Can someone give me a general idea of how you handle version control and deployments in particular using TFS?

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Why is execution-time method resolution faster than compile-time resolution?

- by Felix

At school, we about virtual functions in C++, and how they are resolved (or found, or matched, I don't know what the terminology is -- we're not studying in English) at execution time instead of compile time. The teacher also told us that compile-time resolution is much faster than execution-time (and it would make sense for it to be so). However, a quick experiment would suggest otherwise. I've built this small program: #include <iostream> #include <limits.h> using namespace std; class A { public: void f() { // do nothing } }; class B: public A { public: void f() { // do nothing } }; int main() { unsigned int i; A *a = new B; for (i=0; i < UINT_MAX; i++) a->f(); return 0; } Where I made A::f() once normal, once virtual. Here are my results: [felix@the-machine C]$ time ./normal real 0m25.834s user 0m25.742s sys 0m0.000s [felix@the-machine C]$ time ./virtual real 0m24.630s user 0m24.472s sys 0m0.003s [felix@the-machine C]$ time ./normal real 0m25.860s user 0m25.735s sys 0m0.007s [felix@the-machine C]$ time ./virtual real 0m24.514s user 0m24.475s sys 0m0.000s [felix@the-machine C]$ time ./normal real 0m26.022s user 0m25.795s sys 0m0.013s [felix@the-machine C]$ time ./virtual real 0m24.503s user 0m24.468s sys 0m0.000s There seems to be a steady ~1 second difference in favor of the virtual version. Why is this? Relevant or not: dual-core pentium @ 2.80Ghz, no extra applications running between two tests. Archlinux with gcc 4.5.0. Compiling normally, like: $ g++ test.cpp -o normal Also, -Wall doesn't spit out any warnings, either.

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iPhone app rejection for using ICU (Unicode extensions)

- by nickbit

I received the following mail form Apple, considering my application: *Thank you for submitting your update to ??µ??es?a to the App Store. During our review of your application we found it is using private APIs, which is in violation of the iPhone Developer Program License Agreement section 3.3.1; "3.3.1 Applications may only use Documented APIs in the manner prescribed by Apple and must not use or call any private APIs." While your application has not been rejected, it would be appropriate to resolve this issue in your next update. The following non-public APIs are included in your application: u_isspace ubrk_close ubrk_current ubrk_first ubrk_next ubrk_open If you have defined methods in your source code with the same names as the above mentioned APIs, we suggest altering your method names so that they no longer collide with Apple's private APIs to avoid your application being flagged with future submissions. Please resolve this issue in your next update to ??µ??es?a. Sincerely, iPhone App Review Team* The functions mentioned in this mail are used in the ICU library (International Components for Unicode). Although my app is not rejected at this point, I don't feel very secure for the future of my app, because it relies heavily on the Unicode protocol and on this components in particular. Another thing is that I do not call these functions directly, but they are called by a custom 'sqlite' build (with FTS3 extensions enabled). Am I missing something here? Any suggestions?

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How should I implement lazy session creation in PHP?

- by Adam Franco

By default, PHP's session handling mechanisms set a session cookie header and store a session even if there is no data in the session. If no data is set in the session then I don't want a Set-Cookie header sent to the client in the response and I don't want an empty session record stored on the server. If data is added to $_SESSION, then the normal behavior should continue. My goal is to implement lazy session creation behavior of the sort that Drupal 7 and Pressflow where no session is stored (or session cookie header sent) unless data is added to the $_SESSION array during application execution. The point of this behavior is to allow reverse proxies such as Varnish to cache and serve anonymous traffic while letting authenticated requests pass through to Apache/PHP. Varnish (or another proxy-server) is configured to pass through any requests without cookies, assuming correctly that if a cookie exists then the request is for a particular client. I have ported the session handling code from Pressflow that uses session_set_save_handler() and overrides the implementation of session_write() to check for data in the $_SESSION array before saving and will write this up as library and add an answer here if this is the best/only route to take. My Question: While I can implement a fully custom session_set_save_handler() system, is there an easier way to get this lazy session creation behavior in a relatively generic way that would be transparent to most applications?

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How to minimize total cost of shortest path tree

- by Michael

I have a directed acyclic graph with positive edge-weights. It has a single source and a set of targets (vertices furthest from the source). I find the shortest paths from the source to each target. Some of these paths overlap. What I want is a shortest path tree which minimizes the total sum of weights over all edges. For example, consider two of the targets. Given all edge weights equal, if they share a single shortest path for most of their length, then that is preferable to two mostly non-overlapping shortest paths (fewer edges in the tree equals lower overall cost). Another example: two paths are non-overlapping for a small part of their length, with high cost for the non-overlapping paths, but low cost for the long shared path (low combined cost). On the other hand, two paths are non-overlapping for most of their length, with low costs for the non-overlapping paths, but high cost for the short shared path (also, low combined cost). There are many combinations. I want to find solutions with the lowest overall cost, given all the shortest paths from source to target. Does this ring any bells with anyone? Can anyone point me to relevant algorithms or analogous applications? Cheers!

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.NET assembly loading problem

- by Simon

I'm maintaining the build process for our application which consist of an ASP.Net application, two different Win32 services and other sysadmin related applications. I want to end up with the following configuration to be used both when debugging & deploying. libraires/ -- Contains shared assemblies used by all other apps. web/ -- ASP.Net site service1/ -- Win32 service 1 (seen under the service control manager) service2/ -- Win32 service 2 adminstuff/ -- Sysadmin / support stuff used for troubleshooting The problem is assembly probing privatePath in the app.config does not support relative directories outside the application root. Ie: can't use ../libraries. Very frustating... If I strong name our assemblies, I could use codeBase config element which seems to support absolute path but you need to specify each assembly individually. I also tried hooking into AppDomain.AssemblyResolve event, but I'm getting FileNotFoundException from the .Net Fusion before I can even register the event handler in Main(). I don't like the idea of registering the assemblies in the GAC. Too much hassle when deploying / upgrading application. Is there another to do this without having the specify the path of each requiered assembly ?

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Application log aggregation, management and notifications...

- by Matthew Savage

I'm wondering what everyone is using for logging, log management and log aggregation on their systems. I am working in a company which uses .NET for all it's applications and all systems are Windows based. Currently each application looks after its own logging and notifications of failures (e.g. if app A fails it will send out its own 'call for help' to an admin). While this current practice works its a bit hacky and hard to manage. I've been trying to find some options for making this work better and I've come up with the following: log4net & Chainsaw (ah, if it works). Logging via log4net or another framework into a central database & rolling our own management tool. Logging to the Windows event log and using MOM or System Center Operations Manager to aggregate and manage each of these servers & their apps. A hand-rolled solution to suck all the log files into one point and work some magic across them. Essentially what we are after is something which can pull log entries all together and allow for some analytics to be run across them, plus use a kind of event based system to, for example, send out a warning email when there have been 30+ warning level logs for an application in the last x minutes. So is there anything I've missed, or something someone else can suggest?

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PubSubHubBub Hubs

- by PartlyCloudy

Hi, I'm currently building a live web application based upon the PubSubHubBub protocol. However, I encountered several issues. First, I'm in search of a hub application that I can run on my server. There are several applications, but most of them are not mature yet, or they don't support the 0.3 spec. The official google hub runs on the Google App Engine and can even be executed locally. Unfortunately, "Tasks will not run automatically. Push the 'Run' button to execute each task." This behaviour is useful for debugging and understanding the workflow, but in some live tests, it would be nice not to invoke all tasks manually. Is there a way to tweak the local app engine due automatically run tasks? Next, I have a question concerning the spec itself. The Google reference implementation provides the initial publish method bound to the outpoint uri + /publish. But this is not reflected in the specs. So are there any mature hubs that can be run locally for debugging? Or are there ways to configure the offical google app engine hub to run locally and to execute tasks directly? Thanks in advance

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Threads, Sockets, and Designing Low-Latency, High Concurrency Servers

- by lazyconfabulator

I've been thinking a lot lately about low-latency, high concurrency servers. Specifically, http servers. http servers (fast ones, anyway) can serve thousands of users simultaneously, with very little latency. So how do they do it? As near as I can tell, they all use events. Cherokee and Lighttpd use libevent. Nginx uses it's own event library performing much the same function of libevent, that is, picking a platform optimal strategy for polling events (like kqueue on *bsd, epoll on linux, /dev/poll on Solaris, etc). They all also seem to employ a strategy of multiprocess or multithread once the connection is made - using worker threads to handle the more cpu intensive tasks while another thread continues to listen and handle connections (via events). This is the extent of my understanding and ability to grok the thousand line sources of these applications. What I really want are finer details about how this all works. In examples of using events I've seen (and written) the events are handling both input and output. To this end, do the workers employ some sort of input/output queue to the event handling thread? Or are these worker threads handling their own input and output? I imagine a fixed amount of worker threads are spawned, and connections are lined up and served on demand, but how does the event thread feed these connections to the workers? I've read about FIFO queues and circular buffers, but I've yet to see any implementations to work from. Are there any? Do any use compare-and-swap instructions to avoid locking or is locking less detrimental to event polling than I think? Or have I misread the design entirely? Ultimately, I'd like to take enough away to improve some of my own event-driven network services. Bonus points to anyone providing solid implementation details (especially for stuff like low-latency queues) in C, as that's the language my network services are written in.

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