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• Cache data in SQL CE database

  - by user93422

  Background I have an SQL CE database, that is constantly updated (every second). I have a (web) application that allows a user to look at the data in real-time. At some point a user can click "take a snapshot" button, and it will open the snapshot in a different window. And then on that form, there is "print" and "download" buttons that will either generate a page for printing, or will stream the data as CSV file - but same data snapshot has to be used, i.e. I can't go to the DB to get latest data for that. Details SQL CE dabatase is exposed through WCF web service. Snapshot consists of up to 500 records, 10 columns each. Expiration time on the snapshot of 2 hours is sufficient. It is a low-traffic application, so I don't expect more than few (5) connections at the same time. Loosing snapshot is not a big deal, user can simply generate new one. database is accessed by self-hosted WCF web service using Linq-to-SQL. Web site is ASP.NET MVC hosted on UltiDev Cassini. database, and web site are most likely be on the same box, when deployed. The entire app is intranet bound. Problem I need to cache the snapshot of the data at the moment user pressed "take a snapshot" button, so that I can use same data to generate print page, or generate a file for download. Solution 1: Each time there is a need to generate a snapshot, I will create a table in the database. Since there are no temp tables in SQL CE, I will need to clean it up myself. Solution 2: Cache the snapshot in-memory on either DB server, or web server. Question: Is there anything wrong with proposed solutions? Any different solution suggestions?

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• How to benchmark on multi-core processors

  - by Pascal Cuoq

  I am looking for ways to perform micro-benchmarks on multi-core processors. Context: At about the same time desktop processors introduced out-of-order execution that made performance hard to predict, they, perhaps not coincidentally, also introduced special instructions to get very precise timings. Example of these instructions are rdtsc on x86 and rftb on PowerPC. These instructions gave timings that were more precise than could ever be allowed by a system call, allowed programmers to micro-benchmark their hearts out, for better or for worse. On a yet more modern processor with several cores, some of which sleep some of the time, the counters are not synchronized between cores. We are told that rdtsc is no longer safe to use for benchmarking, but I must have been dozing off when we were explained the alternative solutions. Question: Some systems may save and restore the performance counter and provide an API call to read the proper sum. If you know what this call is for any operating system, please let us know in an answer. Some systems may allow to turn off cores, leaving only one running. I know Mac OS X Leopard does when the right Preference Pane is installed from the Developers Tools. Do you think that this make rdtsc safe to use again? More context: Please assume I know what I am doing when trying to do a micro-benchmark. If you are of the opinion that if an optimization's gains cannot be measured by timing the whole application, it's not worth optimizing, I agree with you, but I cannot time the whole application until the alternative data structure is finished, which will take a long time. In fact, if the micro-benchmark were not promising, I could decide to give up on the implementation now; I need figures to provide in a publication whose deadline I have no control over.

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• Achieving Thread-Safety

  - by Smasher

  Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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• How do I get into a career as a programmer/development DBA?

  - by markle976

  About 8-9 years ago I started getting into programming as a hobby. I started with my TI-86 calculator, and then moved into using Visual Basic. After about a year I started playing around with HTML and JavaScript. Then I discovered Flash; I programmed with Actionscript 2.0 for about 2 years which lead me to start using Coldfusion. After a while I realized that A) I am not a designer, and B) with the way that things were going with AJAX, .NET, and PHP there wasn’t much future in Coldfusion/Actionscript. I had been working mostly as an administrative assistant, but about 3-4 years ago I got a position where I would be doing some web development, and assisting the system admin with supporting windows desktop PCs. I have gotten some decent experience over the past few years, but it has been spread out in somewhat disparate areas: I spend about 40% of my time writing PHP/MySQL and HTML/CSS, etc. I spend about 20% of my time helping users with PC questions. I spend about 20% of my time doing administrative things (mail-merges, excel, etc). I spend about 20% of my time managing / creating reports from our Access Database. I have also taught myself many things on my own, and now have a beginner’s level understanding of things like: Windows Server, Java, Linux, Objective-C, SQL Server, C#, C++, Ruby, Mac OSX, VBA, VBScript, and basic IP networks. I feel like I am in a bit of a rut – I want to get my career moving, but I am not sure what I need to do. If I practice with C# and SQL Server Express for a year will that be enough to get me in the door somewhere? Would it be easier to get a position if I teach myself Linux/Apache since I have more experience with PHP/MySQL?

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• Ajax: Add new <div> from JSON with jQuery

  - by Francesc

  Hi, In a page I have this HTML code: <div id="content"> <div class="container"> <div id="author">@Francesc</div> <div id="message"Hey World!</div <div id="time"13/06/2010 11:53 GMT</div </div> <div class="container"> <div id="author">@SomeOtherUser</div> <div id="message"Bye World!</div <div id="time"13/06/2010 14:53 GMT</div </div> <div class="container"> <div id="author">@Me</div> <div id="message"Hey World!</div <div id="time"13/06/2010 18:53 GMT</div </div> </div> I want to ask, how to get a JSON file, from the server that has more recent messages and put them to the top, I mean above the first <div class="container">. Another question, it's possible to pass with GET when submiting the request to the server, the time of last update? How can I do it? Thanks.

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• Problem with for-loop in python

  - by Protean

  This code is supposed to be able to sort the items in self.array based upon the order of the characters in self.order. The method sort runs properly until the third iteration, unil for some reason the for loop seems to repeat indefinitely. What is going on here? class sorting_class: def __init__(self): self.array = ['ca', 'bd', 'ac', 'ab'] #An array of strings self.arrayt = [] self.globali = 0 self.globalii = 0 self.order = ['a', 'b', 'c', 'd'] #Order of characters self.orderi = 0 self.carry = [] self.leave = [] self.sortedlist = [] def sort(self): for arrayi in self.arrayt: #This should only loop for the number items in self.arrayt. However, the third time this is run it seems to loop indefinitely. print ('run', arrayi) #Shows the problem if self.order[self.orderi] == arrayi[self.globali]: self.carry.append(arrayi) else: if self.globali != 0: self.leave.append(arrayi) def srt(self): self.arrayt = self.array my.sort() #First this runs the first time. while len(self.sortedlist) != len(self.array): if len(self.carry) == 1: self.sortedlist.append(self.carry) self.arrayt = self.leave self.leave = [] self.carry = [] self.globali = 1 self.orderi = 0 my.sort() elif len(self.carry) == 0: if len(self.leave) != 0: #Because nothing matches 'aa' during the second iteration, this code runs the third time" self.arrayt = self.leave self.globali = 1 self.orderi += 1 my.sort() else: self.arrayt = self.array self.globalii += 1 self.orderi = self.globalii self.globali = 0 my.sort() self.orderi = 0 else: #This is what runs the second time. self.arrayt = self.carry self.carry = [] self.globali += 1 my.sort() my = sorting_class() my.srt()

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• Prepare your site images for google image search indexing

  - by Vittorio Vittori

  Hi, I'm trying to understand how can I do to let my site be reachable from google image search spiders. I like how last.fm solution, and I thought to use a technique like his staff do to let google find artists images on their pages. When I'm looking for an artist and I search it on google image search, as often as not I find an image from last.fm artists page, I make an example: If I search the band Pure Reason Revolution It brings me here, the artist's image page http://www.last.fm/music/Pure+Reason+Revolution/+images/4284073 Now if I take a look to the image file, i can see it's named: http://userserve-ak.last.fm/serve/500/4284073/Pure+Reason+Revolution+4.jpg so if I try to undertand how the service works I can try to say: http://userserve-ak.last.fm/serve/ the server who serve the images 500/ the selected size for the image 4284073/ the image id for database Pure+Reason+Revolution+4.jpg the image name I thought it's difficult to think the real filename for the image is Pure+Reason+Revolution+4.jpg for image overwrite problems when an user upload it, in fact if I digit: http://userserve-ak.last.fm/serve/500/4284073.jpg I probably find the real image location and filename With this tecnique the image is highly reachable from search engines and easily archived. My question is, does exist some guide or tutorial to approach on this kind of tecniques, or something similar?

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• How to best launch C++ application from web page

  - by JB

  I guess there are two parts to this question, one technical and one best practice for security and doing things "right". I'm working on a little game using C++ / directx but I would like to be able to launch it from a web page by someone clicking on a link on that page. Ideally I would like the first time they clicked for it to launch an installer downloads and installs the game on their machine, and then the next time to launch an application which updates the game from a web site if it's old and then launches it. I have no problems with the expected security popups and questions the first time it runs. I want people to be certain what they are installing and understand what they are doing. But it would be nice if once it is installed they could run it with the minimum of fuss. My question then is what technologies I could use to do this? I'm thinking that it would need a browser plugin and an activex control so that first time you'd install that, and subsequently the control/plugin would be able to launch the game. I'm not sure that under newer browser secuity models that a plugin would have the permissions to be able to run an installer though or silently invoke applications on the client machine even if they are already installed. Is there a more sensible way to achive what I want to achieve? And I'm worried about the security aspects too. I want this to be convenient for users but I of course want to do it "right". I know this can be done as I've seen several mmorpg type games that launch in this way from the browser now but it's not entirely clear to me how they've done it.

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• How best to deal with warning c4305 when type could change?

  - by identitycrisisuk

  I'm using both Ogre and NxOgre, which both have a Real typedef that is either float or double depending on a compiler flag. This has resulted in most of our compiler warnings now being: warning C4305: 'argument' : truncation from 'double' to 'Ogre::Real' When initialising variables with 0.1 for example. Normally I would use 0.1f but then if you change the compiler flag to double precision then you would get the reverse warning. I guess it's probably best to pick one and stick with it but I'd like to write these in a way that would work for either configuration if possible. One fix would be to use #pragma warning (disable : 4305) in files where it occurs, I don't know if there are any other more complex problems that can be hidden by not having this warning. I understand I would push and pop these in header files too so that they don't end up spreading across code. Another is to create some macro based on the accuracy compiler flag like: #if OGRE_DOUBLE_PRECISION #define INIT_REAL(x) (x) #else #define INIT_REAL(x) static_cast<float>( x ) #endif which would require changing all the variable initialisation done so far but at least it would be future proof. Any preferences or something I haven't thought of?

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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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• Which is faster for large "for" loop: function call or inline coding?

  - by zaplec

  Hi, I have programmed an embedded software (using C of course) and now I'm considering ways to improve the running time of the system. The most important single module in my system is one very large nested for loop module. That module consists of two nested for loops that loops max 122500 times. That's not very much yet, but the problem is that inside that nested for loop I have a function call to a function that is in another source file. That specific function consists mostly of two another nested for loops which loops always 22500 times. So now I have to make a function call 122500 times. I have made that function that is to be called a lot lighter and shorter (yet still works as it should) and now I started to think that would it be faster to rip off that function call and write that process directly inside those first two for loops? The processor in that system is ARM7TDMI and its frequency is 55MHz. The system itself isn't very time critical so it doesn't have to be real time capable. However the faster it can process its duties the better. Also would it be also faster to use while loops instead of fors? And any piece of advice about how to improve the running time is appreciated. -zaplec

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• Formating Date in Freemarker to say "Today", "Yesterday", etc.

  - by egervari

  Is there a way in freemarker to compare dates to test if the date is today or yesterday... or do I have to write code in Java to do these tests? I basically want to do this: <#------------------------------------------------------------------------------ formatDate -------------------------------------------------------------------------------> <#macro formatDate date showTime=true> <#if date??> <span class="Date"> <#if date?is_today> Today <#elseif date?is_yesterday> Yesterday <#else> ${date?date} </#if> </span> <#if showTime> <span class="Time">${date?time}</span> </#if> </#if> </#macro> EDIT: My best guess to implement this is to pass "today" and "yesterday" into the model for the pages that use this function and then compare the date values against these 2 objects in the model. I am out of out of options, but I'd rather not have to do this for every page that uses this macro. Any other options that are nicer? <#if date??> <span class="Date"> <#if date?date?string.short == today?date?string.short> Today <#elseif date?date?string.short == yesterday?date?string.short> Yesterday <#else> ${date?date} </#if> </span> <#if showTime> <span class="Time">${date?time}</span> </#if> </#if>

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• Preventing HTML character entities in locale files from getting munged by Rails3 xss protection

  - by Chris S

  We're building an app, our first using Rails 3, and we're having to build I18n in from the outset. Being perfectionists, we want real typography to be used in our views: dashes, curled quotes, ellipses et al. This means in our locales/xx.yml files we have two choices: Use real UTF-8 characters inline. Should work, but hard to type, and scares me due to the amount of software which still does naughty things to unicode. Use HTML character entities (&#8217; &#8212; etc). Easier to type, and probably more compatible with misbehaving software. I'd rather take the second option, however the auto-escaping in Rails 3 makes this problematic, as the ampersands in the YAML get auto-converted into character entities themselves, resulting in 'visible' &8217;s in the browser. Obviously this can be worked around by using raw on strings, i.e.: raw t('views.signup.organisation_details') But we're not happy going down the route of globally raw-ing every time we t something as it leaves us open to making an error and producing an XSS hole. We could selectively raw strings which we know contain character entities, but this would be hard to scale, and just feels wrong - besides, a string which contains an entity in one language may not in another. Any suggestions on a clever rails-y way to fix this? Or are we doomed to crap typography, xss holes, hours of wasted effort or all thre?

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• how do i implement / build / create an 'in memory database' for my unit test

  - by Michel

  Hi all, i've started unit testing a while ago and as turned out i did more regression testing than unit testing because i also included my database layer thus going to the database verytime. So, implemented Unity to inject a fake database layer, but i of course want to store some data, and the main opinion was: "create an in-memory database" But what is that / how do i implement that? Main question is: i think i have to fake the database layer, but doesn't that make me create a 'simple database' myself or: how can i keep it simple and not rebuilding Sql Server just for my unit tests :) At the end of this question i'll give an explanation of the situation i got in on the project i just started on, and i was wondering if this was the way to go. Michel Current situation i've seen at this client is that testdata is contained in XML files, and there is a 'fake' database layer that connects all the xml files together. For the real database we're using the entity framework, and this works very simple. And now, in the 'fake' layer, i have top create all kind of classes to load, save, persist etc. the data. It sounds weird that there is so much work in the fake layer, and so little in the real layer. I hope this all makes sense :)

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• What category of combinatorial problems appear on the logic games section of the LSAT?

  - by Merjit

  There's a category of logic problem on the LSAT that goes like this: Seven consecutive time slots for a broadcast, numbered in chronological order I through 7, will be filled by six song tapes-G, H, L, O, P, S-and exactly one news tape. Each tape is to be assigned to a different time slot, and no tape is longer than any other tape. The broadcast is subject to the following restrictions: L must be played immediately before O. The news tape must be played at some time after L. There must be exactly two time slots between G and P, regardless of whether G comes before P or whether G comes after P. I'm interested in generating a list of permutations that satisfy the conditions as a way of studying for the test and as a programming challenge. However, I'm not sure what class of permutation problem this is. I've generalized the type problem as follows: Given an n-length array A: How many ways can a set of n unique items be arranged within A? Eg. How many ways are there to rearrange ABCDEFG? If the length of the set of unique items is less than the length of A, how many ways can the set be arranged within A if items in the set may occur more than once? Eg. ABCDEF = AABCDEF; ABBCDEF, etc. How many ways can a set of unique items be arranged within A if the items of the set are subject to "blocking conditions"? My thought is to encode the restrictions and then use something like Python's itertools to generate the permutations. Thoughts and suggestions are welcome.

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• How can I stop a movie (from current frame) playing when I click on next frame - FLASH CS4?

  - by ladygeekgeek

  I have four movie clips (.f4v) in 4 frames in a movie with watch buttons.. This movie has them been imported into a main movie container that has next and previous buttons. However if i play a movie then hit next frame, the movie continues to play in the background. How can I shop this? The code below shows one of the actionscripts for a movie clip and then the main actionscript in the main movie. I am a flash newbie, so all help appreciated. Many thanks. stop(); watch1_btn.addEventListener(MouseEvent.CLICK, playMovie1); function playMovie1(event:MouseEvent):void { movie1_mc.play(); } // Button Listeners next_btn.addEventListener(MouseEvent.CLICK, nextSection); prev_btn.addEventListener(MouseEvent.CLICK, prevSection); function nextSection(event:MouseEvent):void { var thisLabel:String = pages_mc.currentLabel; // gets current frame label as string var thisLabelNum:String = thisLabel.replace("sct", ""); // cuts the leading letters off of the number var curNumber:Number = Number(thisLabelNum); // converts that string number to a real number if (curNumber < 5) { var nextNum:Number = curNumber + 1; // adds 1 to the number so we can go to next frame label pages_mc.gotoAndStop("sct" + nextNum); // This allows us to go to the next frame label } } /////////////////////////////////////////////////////////////////////////// function prevSection(event:MouseEvent):void { var thisLabel:String = pages_mc.currentLabel; // gets current frame label as string var thisLabelNum:String = thisLabel.replace("sct", ""); // cuts the leading letters off of the number var curNumber:Number = Number(thisLabelNum); // converts that string number to a real number var prevNum:Number = curNumber - 1; // subtracts 1 from the number so we can go to next frame label pages_mc.gotoAndStop("sct" + prevNum); // This allows us to go to the previous frame label }

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• Unable to get data from a WCF client

  - by Scott

  I am developing a DLL that will provide sychronized time stamps to multiple applications running on the same machine. The timestamps are altered in a thread that uses a high performance timer and a scalar to provide the appearance of moving faster than real-time. For obvious reasons I want only 1 instance of this time library, and I thought I could use WCF for the other processes to connect to this and poll for timestamps whenever they want. When I connect however I never get a valid time stamp, just an empty DateTime. I should point out that the library does work. The original implementation was a single DLL that each application incorporated and each one was synced using windows messages. I'm fairly sure it has something to do with how I'm setting up the WCF stuff, to which I am still pretty new. Here are the contract definitions: public interface ITimerCallbacks { [OperationContract(IsOneWay = true)] void TimerElapsed(String id); } [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ITimerCallbacks))] public interface ISimTime { [OperationContract] DateTime GetTime(); } Here is my class definition: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] public class SimTimeServer: ISimTime The host setup: // set up WCF interprocess comms host = new ServiceHost(typeof(SimTimeServer), new Uri[] { new Uri("net.pipe://localhost") }); host.AddServiceEndpoint(typeof(ISimTime), new NetNamedPipeBinding(), "SimTime"); host.Open(); and the implementation of the interface function server-side: public DateTime GetTime() { if (ThreadMutex.WaitOne(20)) { RetTime = CurrentTime; ThreadMutex.ReleaseMutex(); } return RetTime; } Lastly the client-side implementation: Callbacks myCallbacks = new Callbacks(); DuplexChannelFactory pipeFactory = new DuplexChannelFactory(myCallbacks, new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/SimTime")); ISimTime pipeProxy = pipeFactory.CreateChannel(); while (true) { string str = Console.ReadLine(); if (str.ToLower().Contains("get")) Console.WriteLine(pipeProxy.GetTime().ToString()); else if (str.ToLower().Contains("exit")) break; }

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• Jquery unidentified data return when post

  - by Nhat Tuan

  <?php //load.php $myid = $_POST['id']; if($myid == 1){ echo '1'; }else if($myid == 0){ echo '0'; } ?> <html> <input id="id" /> <div id="result"></div> <input type="button" id="submit" /> <script type="text/javascript"> $('#submit').click( function(){ var send = 'id=' + $('#id').val(); $.post('load.php', send, function(data){ if(data == 1){ $('#result').html('Success'); }else if(data == 0){ $('#result').html('Failure'); }else{ $('#result').html('Unknow'); } }); }); </script> </html> I test this script in some free host and it work but in my real host jquery unidentified data return and it alway show 'Unknow'. When i change if(data == '1') it show 'Unknow' too EX: input id = 1 click submit & data return is 'Unknow' Why ?? I think this error from host, because i test it in some free host and it work, but now in my real host i got this error, how i can fix it ?

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• Deal with undefined values in code or in the template?

  - by David

  I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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• Would making plain int 64-bit break a lot of reasonable code?

  - by R..

  Until recently, I'd considered the decision by most systems implementors/vendors to keep plain int 32-bit even on 64-bit machines a sort of expedient wart. With modern C99 fixed-size types (int32_t and uint32_t, etc.) the need for there to be a standard integer type of each size 8, 16, 32, and 64 mostly disappears, and it seems like int could just as well be made 64-bit. However, the biggest real consequence of the size of plain int in C comes from the fact that C essentially does not have arithmetic on smaller-than-int types. In particular, if int is larger than 32-bit, the result of any arithmetic on uint32_t values has type signed int, which is rather unsettling. Is this a good reason to keep int permanently fixed at 32-bit on real-world implementations? I'm leaning towards saying yes. It seems to me like there could be a huge class of uses of uint32_t which break when int is larger than 32 bits. Even applying the unary minus or bitwise complement operator becomes dangerous unless you cast back to uint32_t. Of course the same issues apply to uint16_t and uint8_t on current implementations, but everyone seems to be aware of and used to treating them as "smaller-than-int" types.

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• Blackberry (Java) - Can't get KeyListener to work

  - by paullb

  I am trying to get the KeyListener working for Blackberry, but none of the Dialogs pop up indicating that a key has been pressed (see code below, each action has a dialog popup in them). Any ideas on what i might be doing wrong? public class CityInfo extends UiApplication implements KeyListener { static CityInfo application; public static void main(String[] args) { //create a new instance of the application //and start the application on the event thread application.enterEventDispatcher(); } public CityInfo() { //display a new screen application = new CityInfo(); pushScreen(new WorkflowDisplayScreen()); this.addKeyListener(this); } public boolean keyChar(char arg0, int arg1, int arg2) { // TODO Auto-generated method stub Dialog.alert("key pressed : " + arg0); return true; } public boolean keyDown(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyDown : " + keycode); return false; } public boolean keyRepeat(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyRepeat : " + keycode); return false; } public boolean keyStatus(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyStatus : " + keycode); return false; } public boolean keyUp(int keycode, int time) { Dialog.alert("keyUp : " + keycode); // TODO Auto-generated method stub return false; } } I also tried implementing keyChar on the MainScreen class but that did not yield any results either.

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• Expand chaining hashtable. Errors on code.

  - by FILIaS

  Expanding a hashtable with linked lists there are some errors and warnings. I wanna make sure that the following code is right (expand method) and find out what happens that raise these warnings/errors typedef struct { int length; struct List *head; struct List *tail; } HashTable; //resolving collisions using linked lists - chaining typedef struct { char *number; char *name; int time; struct List *next; }List; //on the insert method i wanna check hashtable's size, //if it seems appropriate there is the following code: //Note: hashtable variable is: Hashtable * ...... hashtable = expand(hashtable,number,name,time); /**WARNING**:assignment makes pointer from integer without a cast*/ HashTable* expand( HashTable* h ,char number[10],char* name,int time) /**error**: conflicting types for ‘expand’ previous implicit declaration of ‘expand’ was here*/ { HashTable* new; int n; clientsList *node,*next; PrimesIndex++; int new_size= primes[PrimesIndex]; /* double the size,odd length */ if (!(new=malloc((sizeof( List*))*new_size))) return NULL; for(n=0; n< h->length; ++n) { for(node=h[n].head; node; node=next) { add (&new, node->number, node->name,node->time); next=node->next;//// free(node); } } free(h); return new; }

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• How to create a generic list in this wierd case in c#

  - by Marc Bettex

  Hello, In my program, I have a class A which is extended by B, C and many more classes. I have a method GetInstance() which returns a instance of B or C (or of one of the other child), but I don't know which one, so the return type of the method is A. In the method CreateGenericList(), I have a variable v of type A, which is in fact either a B, a C or another child type and I want to create a generic list of the proper type, i.e. List<B> if v is a B or List<C> if v is a C, ... Currently I do it by using reflection, which works, but this is extremely slow. I wanted to know if there is another way to to it, which doesn't use reflection. Here is an example of the code of my problem: class A { } class B : A { } class C : A { } // More childs of A. class Program { static A GetInstance() { // returns an instance of B or C } static void CreateGenericList() { A v = Program.GetInstance(); IList genericList = // Here I want an instance of List<B> or List<C> or ... depending of the real type of v, not a List<A>. } } I tried the following hack. I call the following method, hoping the type inferencer will guess the type of model, but it doesn't work and return a List<A>. I believe that because c# is statically typed, T is resolved as A and not as the real type of model at runtime. static List<T> CreateGenericListFromModel<T>(T model) where T : A { return new List<T> (); } Does anybody have a solution to that problem that doesn't use reflection or that it is impossible to solve that problem without reflection? Thank you very much, Marc

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• Question about the benefit of using an ORM

  - by johnny

  I want to use an ORM for learning purposes and am try nhibernate. I am using the tutorial and then I have a real project. I can go the "old way" or use an ORM. I'm not sure I totally understand the benefit. On the one hand I can create my abstractions in code such that I can change my databases and be database independent. On the other it seems that if I actually change the database columns I have to change all my code. Why wouldn't I have my application without the ORM, change my database and change my code, instead of changing my database, orm, and code? Is it that they database structure doesn't change that much? I believe there are real benefits because ORMs are used by so many. I'm just not sure I get it yet. Thank you. EDIT: In the tutorial they have many files that are used to make the ORM work http://www.hibernate.org/362.html In the event of an application change, it seems like a lot of extra work just to say that I have "proper" abstraction layers. Because I'm new at it it doesn't look that easy to maintain and again seems like extra work, not less.

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