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• Succinct introduction to C++/CLI for C#/Haskell/F#/JS/C++/... programmer

  - by Henrik

  Hello everybody, I'm trying to write integrations with the operating system and with things like active directory and Ocropus. I know a bunch of programming languages, including those listed in the title. I'm trying to learn exactly how C++/CLI works, but can't find succinct, exact and accurate descriptions online from the searching that I have done. So I ask here. Could you tell me the pitfalls and features of C++/CLI? Assume I know all of C# and start from there. I'm not an expert in C++, so some of my questions' answers might be "just like C++", but could say that I am at C#. I would like to know things like: Converting C++ pointers to CLI pointers, Any differences in passing by value/doubly indirect pointers/CLI pointers from C#/C++ and what is 'recommended'. How do gcnew, __gc, __nogc work with Polymorphism Structs Inner classes Interfaces The "fixed" keyword; does that exist? Compiling DLLs loaded into the kernel with C++/CLI possible? Loaded as device drivers? Invoked by the kernel? What does this mean anyway (i.e. to load something into the kernel exactly; how do I know if it is?)? L"my string" versus "my string"? wchar_t? How many types of chars are there? Are we safe in treating chars as uint32s or what should one treat them as to guarantee language indifference in code? Finalizers (~ClassName() {}) are discouraged in C# because there are no garantuees they will run deterministically, but since in C++ I have to use "delete" or use copy-c'tors as to stack allocate memory, what are the recommendations between C#/C++ interactions? What are the pitfalls when using reflection in C++/CLI? How well does C++/CLI work with the IDisposable pattern and with SafeHandle, SafeHandleZeroOrMinusOneIsInvalid? I've read briefly about asynchronous exceptions when doing DMA-operations, what are these? Are there limitations you impose upon yourself when using C++ with CLI integration rather than just doing plain C++? Attributes in C++ similar to Attributes in C#? Can I use the full meta-programming patterns available in C++ through templates now and still have it compile like ordinary C++? Have you tried writing C++/CLI with boost? What are the optimal ways of interfacing the boost library with C++/CLI; can you give me an example of passing a lambda expression to an iterator/foldr function? What is the preferred way of exception handling? Can C++/CLI catch managed exceptions now? How well does dynamic IL generation work with C++/CLI? Does it run on Mono? Any other things I ought to know about?

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• How to produce precisely-timed tone and silence in C#

  - by Bob Denny

  I have a C# project that plays Morse code for RSS feeds. I write it using Managed DirectX, only to discover that Managed DirectX is old and deprecated. The task I have is to play pure sine wave bursts interspersed with silence periods (the code) which are precisely timed as to their duration. I need to be able to call a function which plays a pure tone for so many milliseconds, then Thread.Sleep() then play another, etc. At its fastest, the tones and spaces can be as short as 40ms. It's working quite well in Managed DirectX. To get the precisely timed tone I create 1 sec. of sine wave into a secondary buffer, then to play a tone of a certain duration I seek forward to within x milliseconds of the end of the buffer then play. I've tried System.Media.SoundPlayer. It's a loser because you have to Play(), Sleep(), then Stop() for arbitrary tone lengths. The result is a tone that is too long, variable by CPU load. It takes an indeterminate amount of time to actually stop the tone. I then embarked on a lengthy attempt to use NAudio 1.3. I ended up with a memory resident stream providing the tone data, and again seeking forward leaving the desired length of tone remaining in the stream, then playing. This worked OK on the DirectSoundOut class for a while (see below) but the WaveOut class quickly dies with an internal assert saying that buffers are still on the queue despite PlayerStopped = true. This is odd since I play to the end then put a wait of the same duration between the end of the tone and the start of the next. You'd think that 80ms after starting Play of a 40 ms tone that it wouldn't have buffers on the queue. DirectSoundOut works well for a while, but its problem is that for every tone burst Play() it spins off a separate thread. Eventually (5 min or so) it just stops working. You can see thread after thread after thread exiting in the Output window while running the project in VS2008 IDE. I don't create new objects during playing, I just Seek() the tone stream then call Play() over and over, so I don't think it's a problem with orphaned buffers/whatever piling up till it's choked. I'm out of patience on this one, so I'm asking in the hopes that someone here has faced a similar requirement and can steer me in a direction with a likely solution. Thanks in advance...

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• Why does this thumbnail generation code throw OutOfMemoryException on large files?

  - by tsilb

  This code works great for generating thumbnails, but when given a very large (100MB+) TIFF file, it throws OutOfMemoryExceptions. When I do it manually in Paint.NET on the same machine, it works fine. How can I improve this code to stop throwing on very large files? In this case I'm loading a 721MB TIF on a machine with 8GB RAM. The Task Manager shows 2GB used so something is preventing it from using all that memory. Specifically it throws when I load the Image to calculate the size of the original. What gives? /// <summary>Creates a thumbnail of a given image.</summary> /// <param name="inFile">Fully qualified path to file to create a thumbnail of</param> /// <param name="outFile">Fully qualified path to created thumbnail</param> /// <param name="x">Width of thumbnail</param> /// <returns>flag; result = is success</returns> public static bool CreateThumbnail(string inFile, string outFile, int x) { // Validation - assume 16x16 icon is smallest useful size. Smaller than that is just not going to do us any good anyway. I consider that an "Exceptional" case. if (string.IsNullOrEmpty(inFile)) throw new ArgumentNullException("inFile"); if (string.IsNullOrEmpty(outFile)) throw new ArgumentNullException("outFile"); if (x < 16) throw new ArgumentOutOfRangeException("x"); if (!File.Exists(inFile)) throw new ArgumentOutOfRangeException("inFile", "File does not exist: " + inFile); // Mathematically determine Y dimension int y; using (Image img = Image.FromFile(inFile)) { // OutOfMemoryException double xyRatio = (double)x / (double)img.Width; y = (int)((double)img.Height * xyRatio); } // All this crap could have easily been Image.Save(filename, x, y)... but nooooo.... using (Bitmap bmp = new Bitmap(inFile)) using (Bitmap thumb = new Bitmap((Image)bmp, new Size(x, y))) using (Graphics g = Graphics.FromImage(thumb)) { g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality; System.Drawing.Imaging.ImageCodecInfo codec = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders()[1]; System.Drawing.Imaging.EncoderParameters ep2 = new System.Drawing.Imaging.EncoderParameters(1); ep2.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L); g.DrawImage(bmp, new Rectangle(0,0,thumb.Width, thumb.Height)); try { thumb.Save(outFile, codec, ep2); return true; } catch { return false; } } }

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• Data access pattern

  - by andlju

  I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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• Integers not properly returned from a property list (plist) array in Objective-C

  - by Gaurav

  In summary, I am having a problem where I read what I expect to be an NSNumber from an NSArray contained in a property list and instead of getting a number such as '1', I get what looks to be a memory address (i.e. '61879840'). The numbers are clearly correct in the property list. Below is my process for creating the property list and reading it back. Creating the property list I have created a simple Objective-C property list with arrays of integers within one root array: <array> <array> <integer>1</integer> <integer>2</integer> </array> <array> <integer>1</integer> <integer>2</integer> <integer>5</integer> </array> ... more arrays with integers ... </array> The arrays are NSArray objects and the integers are NSNumber objects. The property list has been created and serialized using the following code: // factorArray is an NSArray that contains NSArrays of NSNumbers as described above // serialize and compress factorArray as a property list, Factors-bin.plist NSString *error; NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; NSString *plistPath = [rootPath stringByAppendingPathComponent:@"Factors-bin.plist"]; NSData *plistData = [NSPropertyListSerialization dataFromPropertyList:factorArray format:NSPropertyListBinaryFormat_v1_0 errorDescription:&error]; Inspecting the created plist, all values and types are correct. Reading the property list The property list is read in as Data and then converted to an NSArray: NSString *path = [[NSBundle mainBundle] pathForResource:@"Factors" ofType:@"plist"]; NSData *plistData = [[NSData alloc] initWithContentsOfFile:path]; NSPropertyListFormat format; NSString *error = nil; NSArray *factorData = (NSArray *)[NSPropertyListSerialization propertyListFromData:plistData mutabilityOption:NSPropertyListImmutable format:&format errorDescription:&error]; Cycling through factorData to see what it contains is where I see the erroneous integers: for (int i = 0; i < 10; i++) { NSArray *factorList = (NSArray *)[factorData objectAtIndex:i]; NSLog(@"Factors of %d\n", i + 1); for (int j = 0; j < [factorList count]; j++) { NSLog(@" %d\n", (NSNumber *)[factorList objectAtIndex:j]); } } I see all the correct number of values, but the values themselves are incorrect, i.e.: Factors of 3 61879840 (should be 1) 61961200 (should be 3) Factors of 4 61879840 (should be 1) 61943472 (should be 2) 61943632 (should be 4) Factors of 5 61879840 (should be 1) 61943616 (should be 5)

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• Problem with signal handlers being called too many times [closed]

  - by Hristo

  how can something print 3 times when it only goes the printing code twice? I'm coding in C and the code is in a SIGCHLD signal handler I created. void chld_signalHandler() { int pidadf = (int) getpid(); printf("pidafdfaddf: %d\n", pidadf); while (1) { int termChildPID = waitpid(-1, NULL, WNOHANG); if (termChildPID == 0 || termChildPID == -1) { break; } dll_node_t *temp = head; while (temp != NULL) { printf("stuff\n"); if (temp->pid == termChildPID && temp->type == WORK) { printf("inside if\n"); // read memory mapped file b/w WORKER and MAIN // get statistics and write results to pipe char resultString[256]; // printing TIME int i; for (i = 0; i < 24; i++) { sprintf(resultString, "TIME; %d ; %d ; %d ; %s\n",i,1,2,temp->stats->mboxFileName); fwrite(resultString, strlen(resultString), 1, pipeFD); } remove_node(temp); break; } temp = temp->next; } printf("done printing from sigchld \n"); } return; } the output for my MAIN process is this: MAIN PROCESS 16214 created WORKER PROCESS 16220 for file class.sp10.cs241.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld MAIN PROCESS 16214 created WORKER PROCESS 16221 for file class.sp10.cs225.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld and the output for the MONITOR process is this: MONITOR: pipe is open for reading MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs241.mbox MONITOR: end of readpipe ( I've taken out repeating lines so I don't take up so much space ) Thanks, Hristo

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• AVAudioPlayer crash after playing from an AVAudioRecord

  - by munchine

  I've got a button the user tap to start recording and tap again to stop. When it stop I want the recorded voice 'echo' back so the user can hear what was recorded. This works fine the first time. If I hit the button for the third time, it starts a new recording and when I hit stop it crashes with EXC_BAD_ACCESS. - (IBAction) readToMeTapped { if(recording) { recording = NO; [readToMeButton setTitle:@"Stop Recording" forState: UIControlStateNormal ]; NSMutableDictionary *recordSetting = [[NSDictionary alloc] initWithObjectsAndKeys: [NSNumber numberWithFloat: 44100.0], AVSampleRateKey, [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey, [NSNumber numberWithInt: 1], AVNumberOfChannelsKey, [NSNumber numberWithInt: AVAudioQualityMax], AVEncoderAudioQualityKey, nil]; // Create a new dated file NSDate *now = [NSDate dateWithTimeIntervalSinceNow:0]; NSString *caldate = [now description]; recordedTmpFile = [NSURL fileURLWithPath:[[NSString stringWithFormat:@"%@/%@.caf", DOCUMENTS_FOLDER, caldate] retain]]; error = nil; recorder = [[ AVAudioRecorder alloc] initWithURL:recordedTmpFile settings:recordSetting error:&error]; if(!recorder){ NSLog(@"recorder: %@ %d %@", [error domain], [error code], [[error userInfo] description]); UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Warning" message: [error localizedDescription] delegate: nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; [alert release]; return; } NSLog(@"Using File called: %@",recordedTmpFile); //Setup the recorder to use this file and record to it. [recorder setDelegate:self]; [recorder prepareToRecord]; [recorder recordForDuration:(NSTimeInterval) 5]; //recording for a limited time } else { // it crashes the second time it gets here! recording = YES; NSLog(@"Recording YES Using File called: %@",recordedTmpFile); [readToMeButton setTitle:@"Start Recording" forState:UIControlStateNormal ]; [recorder stop]; //Stop the recorder. //playback recording AVAudioPlayer * newPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:recordedTmpFile error:&error]; [recordedTmpFile release]; self.aPlayer = newPlayer; [newPlayer release]; [aPlayer setDelegate:self]; [aPlayer prepareToPlay]; [aPlayer play]; } } - (void)audioRecorderDidFinishRecording:(AVAudioRecorder *)sender successfully:(BOOL)flag { NSLog (@"audioRecorderDidFinishRecording:successfully:"); [recorder release]; recorder = nil; } Checking the debugger, it flags the error here @synthesize aPlayer, recorder; This is the part I don't understand. I thought it may have something to do with releasing memory but I've been careful. Have I missed something?

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• Regular exp to validate email in C

  - by Liju Mathew

  Hi, We need to write a email validation program in C. We are planning to use GNU Cregex.h) regular expression. The regular expression we prepared is [a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])? But the below code is failing while compiling the regex. #include <stdio.h> #include <regex.h> int main(const char *argv, int argc) { const char *reg_exp = "[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?"; int status = 1; char email[71]; regex_t preg; int rc; printf("The regex = %s\n", reg_exp); rc = regcomp(&preg, reg_exp, REG_EXTENDED|REG_NOSUB); if (rc != 0) { if (rc == REG_BADPAT || rc == REG_ECOLLATE) fprintf(stderr, "Bad Regex/Collate\n"); if (rc == REG_ECTYPE) fprintf(stderr, "Invalid Char\n"); if (rc == REG_EESCAPE) fprintf(stderr, "Trailing \\\n"); if (rc == REG_ESUBREG || rc == REG_EBRACK) fprintf(stderr, "Invalid number/[] error\n"); if (rc == REG_EPAREN || rc == REG_EBRACE) fprintf(stderr, "Paren/Bracket error\n"); if (rc == REG_BADBR || rc == REG_ERANGE) fprintf(stderr, "{} content invalid/Invalid endpoint\n"); if (rc == REG_ESPACE) fprintf(stderr, "Memory error\n"); if (rc == REG_BADRPT) fprintf(stderr, "Invalid regex\n"); fprintf(stderr, "%s: Failed to compile the regular expression:%d\n", __func__, rc); return 1; } while (status) { fgets(email, sizeof(email), stdin); status = email[0]-48; rc = regexec(&preg, email, (size_t)0, NULL, 0); if (rc == 0) { fprintf(stderr, "%s: The regular expression is a match\n", __func__); } else { fprintf(stderr, "%s: The regular expression is not a match: %d\n", __func__, rc); } } regfree(&preg); return 0; } The regex compilation is failing with the below error. The regex = [a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])? Invalid regex main: Failed to compile the regular expression:13 What is the cause of this error? Whether the regex need to be modified? Thanks, Mathew Liju

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• Mootools - how to destroy a class instance

  - by Rob

  What I'm trying to do is create a class that I can quickly attach to links, that will fetch and display a thumbnail preview of the document being linked to. Now, I am focusing on ease of use and portability here, I want to simply add a mouseover event to links like this: <a href="some-document.pdf" onmouseover="new TestClass(this)">Testing</a> I realize there are other ways I can go about this that would solve my issue here, and I may end up having to do that, but right now my goal is to implement this as above. I don't want to manually add a mouseout event to each link, and I don't want code anywhere other than within the class (and the mouseover event creating the class instance). The code: TestClass = new Class({ initialize: function(anchor) { this.anchor = $(anchor); if(!this.anchor) return; if(!window.zzz) window.zzz = 0; this.id = ++window.zzz; this.anchor.addEvent('mouseout', function() { // i need to get a reference to this function this.hide(); }.bind(this)); this.show(); }, show: function() { // TODO: cool web 2.0 stuff here! }, hide: function() { alert(this.id); //this.removeEvent('mouseout', ?); // need reference to the function to remove /*** this works, but what if there are unrelated mouseout events? and the class instance still exists! ***/ //this.anchor.removeEvents('mouseout'); //delete(this); // does not work ! //this = null; // invalid assignment! //this = undefined; // invalid assignment! } }); What currently happens with the above code: 1st time out: alerts 1 2nd time out: alerts 1, 2 3rd time out: alerts 1, 2, 3 etc Desired behavior: 1st time out: alerts 1 2nd time out: alerts 2 3rd time out: alerts 3 etc The problem is, each time I mouse over the link, I'm creating a new class instance and appending a new mouseout event for that instance. The class instance also remains in memory indefinitely. On mouseout I need to remove the mouseout event and destroy the class instance, so on subsequent mouseovers we are starting fresh.

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• How do you handle EF Data Contexts combined with asp.net custom membership/role providers

  - by KallDrexx

  I can't seem to get my head around how to implement a custom membership provider with Entity Framework data contexts into my asp.net MVC application. I understand how to create a custom membership/role provider by itself (using this as a reference). Here's my current setup: As of now I have a repository factory interface that allows different repository factories to be created (right now I only have a factory for EF repositories and and in memory repositories). The repository factory looks like this: public class EFRepositoryFactory : IRepositoryFactory { private EntitiesContainer _entitiesContext; /// <summary> /// Constructor that generates the necessary object contexts /// </summary> public EFRepositoryFactory() { _entitiesContext = new EntitiesContainer(); } /// <summary> /// Generates a new entity framework repository for the specified entity type /// </summary> /// <typeparam name="T">Type of entity to generate a repository for </typeparam> /// <returns>Returns an EFRepository</returns> public IRepository<T> GenerateRepository<T>() where T : class { return new EFRepository<T>(_entitiesContext); } } Controllers are passed an EF repository factory via castle Windsor. The controller then creates all the service/business layer objects it requires and passes in the repository factory into it. This means that all service objects are using the same EF data contexts and I do not have to worry about objects being used in more than one data context (which of course is not allowed and causes an exception). As of right now I am trying to decide how to generate my user and authorization service layers, and have run against a design roadblock. The User/Authization service will be a central class that handles the logic for logging in, changing user details, managing roles and determining what users have access to what. The problem is, using the current methodology the asp.net mvc controllers will initialize it's own EF repository factory via Windsor and the asp.net membership/role provider will have to initialize it's own EF repository factory. This means that each part of the site will then have it's own data context. This seems to mean that if asp.net authenticates a user, that user's object will be in the membership provider's data context and thus if I try to retrieve that user object in the service layer (say to change the user's name) I will get a duplication exception. I thought of making the repository factory class a singleton, but I don't see a way for that to work with castle Windsor. How do other people handle asp.net custom providers in a MVC (or any n-tier) architecture without having object duplication issues?

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• Problem with signal handlers

  - by Hristo

  how can something print 3 times when it only goes the printing code twice? I'm coding in C and the code is in a SIGCHLD signal handler I created. void chld_signalHandler() { int pidadf = (int) getpid(); printf("pidafdfaddf: %d\n", pidadf); while (1) { int termChildPID = waitpid(-1, NULL, WNOHANG); if (termChildPID == 0 || termChildPID == -1) { break; } dll_node_t *temp = head; while (temp != NULL) { printf("stuff\n"); if (temp->pid == termChildPID && temp->type == WORK) { printf("inside if\n"); // read memory mapped file b/w WORKER and MAIN // get statistics and write results to pipe char resultString[256]; // printing TIME int i; for (i = 0; i < 24; i++) { sprintf(resultString, "TIME; %d ; %d ; %d ; %s\n",i,1,2,temp->stats->mboxFileName); fwrite(resultString, strlen(resultString), 1, pipeFD); } remove_node(temp); break; } temp = temp->next; } printf("done printing from sigchld \n"); } return; } the output for my MAIN process is this: MAIN PROCESS 16214 created WORKER PROCESS 16220 for file class.sp10.cs241.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld MAIN PROCESS 16214 created WORKER PROCESS 16221 for file class.sp10.cs225.mbox pidafdfaddf: 16214 stuff stuff inside if done printing from sigchld and the output for the MONITOR process is this: MONITOR: pipe is open for reading MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs225.mbox MONITOR PIPE: TIME; 0 ; 1 ; 2 ; class.sp10.cs241.mbox MONITOR: end of readpipe ( I've taken out repeating lines so I don't take up so much space ) Thanks, Hristo

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• How to integrate Purify into Hudson CI?

  - by Martin

  Hello everybody! I have a Hudson CI system set up and for the moment it is used for building a project and running some unit tests. My next step is to integrate the memory leak detector Purify into the build cycle. Now I want to start the unit tests also inside purify and for this I have created a new batch task which runs following command: purify.exe /SaveTextData MyExecutable.exe --test TestLibrary.dll --output xml As I read in the Purify documentation the /SaveTextData option is used in order to run purify not in GUI mode. If I run this command on my local workstation in the command line it works perfectly. But in case it is started by Hudson, nothing happens. Unfortunetly there are no logs of purify... Has someone ever tried to start purify either by Hudson or any other CI system? Thanks in advance. Best regards Martin EDIT: I forgot to tell you, that I have Hudson running as master and slave on different computers. On the master I have configured a task which should start the unit tests within purify on the slave. I am running the slave via JNLP. EDIT 18.03.2010: Ok, so finally I am a bit closer the source of the problem. I have discovered, that running my unit tests in purify locally the log file EngineCmdLine.log contains three commands. I am starting purify with following command: purify.exe /SaveTextData TestRunnerConsoleWD.exe --test TestDemoWD.dll Output of EngineCmdLine.log when starting purify manually: File: D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestRunnerConsoleWD.exe File: C:\WINDOWS\system32\ws2_32.dll File: D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestDemoWD.dll Output when starting via Hudson: File: D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestRunnerConsoleWD.exe File: C:\WINDOWS\system32\ws2_32.dll File: D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestDemoWD.dll File: D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestDemoWD.dll The error output of purify: Instrumenting: BtcTestDemoWD.dll 313856 bytes Purify: While processing file D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TESTFWWD.DLL: Error: Cannot replace file c:\Programme\IBM\RationalPurifyPlus\PurifyPlus\cache\BTCTESTFWWD$Purify_D_workspace_hudson_workspace_Purify_TestFW_CommonsCoreTest_Cpp_msvs9.DLL. Is it in use? TESTFWWD.DLL 505344 bytes Unable to instrument D:\workspace\hudson\workspace\Purify_TestFW_CommonsCoreTest_Cpp_msvs9\TestDemoWD.dll (0x1) Question is, why is purify starting twice a command with the TestDemoWD.dll library?

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• wrapping boost::ublas with swig

  - by leon

  I am trying to pass data around the numpy and boost::ublas layers. I have written an ultra thin wrapper because swig cannot parse ublas' header correctly. The code is shown below #include <boost/numeric/ublas/vector.hpp> #include <boost/numeric/ublas/matrix.hpp> #include <boost/lexical_cast.hpp> #include <algorithm> #include <sstream> #include <string> using std::copy; using namespace boost; typedef boost::numeric::ublas::matrix<double> dm; typedef boost::numeric::ublas::vector<double> dv; class dvector : public dv{ public: dvector(const int rhs):dv(rhs){;}; dvector(); dvector(const int size, double* ptr):dv(size){ copy(ptr, ptr+sizeof(double)*size, &(dv::data()[0])); } ~dvector(){} }; with the SWIG interface that looks something like %apply(int DIM1, double* INPLACE_ARRAY1) {(const int size, double* ptr)} class dvector{ public: dvector(const int rhs); dvector(); dvector(const int size, double* ptr); %newobject toString; char* toString(); ~dvector(); }; I have compiled them successfully via gcc 4.3 and vc++9.0. However when I simply run a = dvector(array([1.,2.,3.])) it gives me a segfault. This is the first time I use swigh with numpy and not have fully understanding between the data conversion and memory buffer passing. Does anyone see something obvious I have missed? I have tried to trace through with a debugger but it crashed within the assmeblys of python.exe. I have no clue if this is a swig problem or of my simple wrapper. Anything is appreciated.

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• Floating point vs integer calculations on modern hardware

  - by maxpenguin

  I am doing some performance critical work in C++, and we are currently using integer calculations for problems that are inherently floating point because "its faster". This causes a whole lot of annoying problems and adds a lot of annoying code. Now, I remember reading about how floating point calculations were so slow approximately circa the 386 days, where I believe (IIRC) that there was an optional co-proccessor. But surely nowadays with exponentially more complex and powerful CPUs it makes no difference in "speed" if doing floating point or integer calculation? Especially since the actual calculation time is tiny compared to something like causing a pipeline stall or fetching something from main memory? I know the correct answer is to benchmark on the target hardware, what would be a good way to test this? I wrote two tiny C++ programs and compared their run time with "time" on Linux, but the actual run time is too variable (doesn't help I am running on a virtual server). Short of spending my entire day running hundreds of benchmarks, making graphs etc. is there something I can do to get a reasonable test of the relative speed? Any ideas or thoughts? Am I completely wrong? The programs I used as follows, they are not identical by any means: #include <iostream> #include <cmath> #include <cstdlib> #include <time.h> int main( int argc, char** argv ) { int accum = 0; srand( time( NULL ) ); for( unsigned int i = 0; i < 100000000; ++i ) { accum += rand( ) % 365; } std::cout << accum << std::endl; return 0; } Program 2: #include <iostream> #include <cmath> #include <cstdlib> #include <time.h> int main( int argc, char** argv ) { float accum = 0; srand( time( NULL ) ); for( unsigned int i = 0; i < 100000000; ++i ) { accum += (float)( rand( ) % 365 ); } std::cout << accum << std::endl; return 0; } Thanks in advance!

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• Is x a reserved keyword in Javascript FF/Safari not in IE?

  - by Marco Demaio

  A web page of a web application was showing a strange error. I regressively removed all the HTML/CSS/JS code and arrived to the basic and simple code below. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html><head> <title>test</title> <script type="text/javascript"> var TestObj = { foo: function() {} } alert(x); //ok displays "undefined" var x = TestObj.foo; var z = TestObj.foo; </script> </head><body> <p onclick='alert(x);'>Click shows function foo!</p> <img onclick='alert(x);' alt='CRAZY click displays a number in FF/Safari not function foo' src='' style='display: block; width: 100px; height: 100px; border: 1px solid #00ff00;'> <p onclick='alert(x);'>Click shows function foo!</p> </body></html> It's crazy: when clicking on P elements the string "function(){}" is displaied as expected. But when clicking on IMG element it shows a number as if x function got in some way removed from memory or deinstantiated (it does not even show x as "undefined" but as a number). To let you test it quickly I placed the working test above also here. This can be reproduced on both Firefox 3.6 and Safari 4.0.4. Everything works properly only on IE7+. I'm really clueless, I was wondering if x is maybe a reserved keyword in JS Firefox/Safari. Thanks to anyone who could help! FYI: if you repalce x() with z() everything work prefectly in all browsers (this is even more crazy to me) adding a real image in src attribute does not fix the problem removing style in img does not fix the problem (i gave style to image only to help you clicking on image thus you can see the imnage border)

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• Tunnel over HTTPS

  - by ephemient

  At my workplace, the traffic blocker/firewall has been getting progressively worse. I can't connect to my home machine on port 22, and lack of ssh access makes me sad. I was previously able to use SSH by moving it to port 5050, but I think some recent filters now treat this traffic as IM and redirect it through another proxy, maybe. That's my best guess; in any case, my ssh connections now terminate before I get to log in. These days I've been using Ajaxterm over HTTPS, as port 443 is still unmolested, but this is far from ideal. (Sucky terminal emulation, lack of port forwarding, my browser leaks memory at an amazing rate...) I tried setting up mod_proxy_connect on top of mod_ssl, with the idea that I could send a CONNECT localhost:22 HTTP/1.1 request through HTTPS, and then I'd be all set. Sadly, this seems to not work; the HTTPS connection works, up until I finish sending my request; then SSL craps out. It appears as though mod_proxy_connect takes over the whole connection instead of continuing to pipe through mod_ssl, confusing the heck out of the HTTPS client. Is there a way to get this to work? I don't want to do this over plain HTTP, for several reasons: Leaving a big fat open proxy like that just stinks A big fat open proxy is not good over HTTPS either, but with authentication required it feels fine to me HTTP goes through a proxy -- I'm not too concerned about my traffic being sniffed, as it's ssh that'll be going "plaintext" through the tunnel -- but it's a lot more likely to be mangled than HTTPS, which fundamentally cannot be proxied Requirements: Must work over port 443, without disturbing other HTTPS traffic (i.e. I can't just put the ssh server on port 443, because I would no longer be able to serve pages over HTTPS) I have or can write a simple port forwarder client that runs under Windows (or Cygwin) Edit DAG: Tunnelling SSH over HTTP(S) has been pointed out to me, but it doesn't help: at the end of the article, they mention Bug 29744 - CONNECT does not work over existing SSL connection preventing tunnelling over HTTPS, exactly the problem I was running into. At this point, I am probably looking at some CGI script, but I don't want to list that as a requirement if there's better solutions available.

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• Java Hardware Acceleration

  - by Freezerburn

  I have been spending some time looking into the hardware acceleration features of Java, and I am still a bit confused as none of the sites that I found online directly and clearly answered some of the questions I have. So here are the questions I have for hardware acceleration in Java: 1) In Eclipse version 3.6.0, with the most recent Java update for Mac OS X (1.6u10 I think), is hardware acceleration enabled by default? I read somewhere that someCanvas.getGraphicsConfiguration().getBufferCapabilities().isPageFlipping() is supposed to give an indication of whether or not hardware acceleration is enabled, and my program reports back true when that is run on my main Canvas instance for drawing to. If my hardware acceleration is not enabled now, or by default, what would I have to do to enable it? 2) I have seen a couple articles here and there about the difference between a BufferedImage and VolatileImage, mainly saying that VolatileImage is the hardware accelerated image and is stored in VRAM for fast copy-from operations. However, I have also found some instances where BufferedImage is said to be hardware accelerated as well. Is BufferedImage hardware accelerated as well in my environment? What would be the advantage of using a VolatileImage if both types are hardware accelerated? My main assumption for the advantage of having a VolatileImage in the case of both having acceleration is that VolatileImage is able to detect when its VRAM has been dumped. But if BufferedImage also support acceleration now, would it not have the same kind of detection built into it as well, just hidden from the user, in case that the memory is dumped? 3) Is there any advantage to using someGraphicsConfiguration.getCompatibleImage/getCompatibleVolatileImage() as opposed to ImageIO.read() In a tutorial I have been reading for some general concepts about setting up the rendering window properly (tutorial) it uses the getCompatibleImage method, which I believe returns a BufferedImage, to get their "hardware accelerated" images for fast drawing, which ties into question 2 about if it is hardware accelerated. 4) This is less hardware acceleration, but it is something I have been curious about: do I need to order which graphics get drawn? I know that when using OpenGL via C/C++ it is best to make sure that the same graphic is drawn in all the locations it needs to be drawn at once to reduce the number of times the current texture needs to be switch. From what I have read, it seems as if Java will take care of this for me and make sure things are drawn in the most optimal fashion, but again, nothing has ever said anything like this clearly. 5) What AWT/Swing classes support hardware acceleration, and which ones should be used? I am currently using a class that extends JFrame to create a window, and adding a Canvas to it from which I create a BufferStrategy. Is this good practice, or is there some other type of way I should be implementing this? Thank you very much for your time, and I hope I provided clear questions and enough information for you to answer my several questions.

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• NSDocument Subclass not closed by NSWindowController?

  - by Nathan Douglas

  Okay, I'm fairly new to Cocoa and Objective-C, and to OOP in general. As background, I'm working on an extensible editor that stores the user's documents in a package. This of course required some "fun" to get around some issues with NSFileWrapper (i.e. a somewhat sneaky writing and loading process to avoid making NSFileWrappers for every single document within the bundle). The solution I arrived at was to essentially treat my NSDocument subclass as just a shell -- use it to make the folder for the bundle, and then pass off writing the actual content of the document to other methods. Unfortunately, at some point I seem to have completely screwed the pooch. I don't know how this happened, but closing the document window no longer releases the document. The document object doesn't seem to receive a "close" message -- or any related messages -- even though the window closes successfully. The end result is that if I start my app, create a new document, save it, then close it, and try to reopen it, the document window never appears. With some creative subclassing and NSLogging, I managed to figure out that the document object was still in memory, and still attached to the NSDocumentController instance, and so trying to open the document never got past the NSDocumentController's "hmm, currently have that one open" check. I did have an NSWindowController and NSDocumentController instance, but I've purged them from my project completely. I've overridden nearly every method for NSDocument trying to find out where the issue is. So far as I know, my Interface Builder bindings are all correct -- "Close" in the main menu is attached to "performClose:" of the First Responder, etc, and I've tried with fresh unsullied MainMenu and Document xibs as well. I thought that it might be something strange with my bundle writing code, so I basically deleted it all and started from scratch, but that didn't seem to work. I took out my init method overrides, and that didn't help either. I don't have the source of any simple document apps here, so I didn't try the next logical step (to substitute known-working code for mine in the readfromurl and writetourl methods). I've had this problem for about sixteen hours of uninterrupted troubleshooting now, and needless to say, I'm at the end of my rope. If I can't figure it out, I guess I'm going to try the project from scratch with a lot more code and intensity based around the bundle-document mess. Any help would be greatly appreciated.

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• quartz: preventing concurrent instances of a job in jobs.xml

  - by Jason S

  This should be really easy. I'm using Quartz running under Apache Tomcat 6.0.18, and I have a jobs.xml file which sets up my scheduled job that runs every minute. What I would like to do, is if the job is still running when the next trigger time rolls around, I don't want to start a new job, so I can let the old instance complete. Is there a way to specify this in jobs.xml (prevent concurrent instances)? If not, is there a way I can share access to an in-memory singleton within my application's Job implementation (is this through the JobExecutionContext?) so I can handle the concurrency myself? (and detect if a previous instance is running) update: After floundering around in the docs, here's a couple of approaches I am considering, but either don't know how to get them to work, or there are problems. Use StatefulJob. This prevents concurrent access... but I'm not sure what other side-effects would occur if I use it, also I want to avoid the following situation: Suppose trigger times would be every minute, i.e. trigger#0 = at time 0, trigger #1 = 60000msec, #2 = 120000, #3 = 180000, etc. and the trigger#0 at time 0 fires my job which takes 130000msec. With a plain Job, this would execute triggers #1 and #2 while job trigger #0 is still running. With a StatefulJob, this would execute triggers #1 and #2 in order, immediately after #0 finishes at 130000. I don't want that, I want #1 and #2 not to run and the next trigger that runs a job should take place at #3 (180000msec). So I still have to do something else with StatefulJob to get it to work the way I want, so I don't see much of an advantage to using it. Use a TriggerListener to return true from vetoJobExecution(). Although implementing the interface seems straightforward, I have to figure out how to setup one instance of a TriggerListener declaratively. Can't find the docs for the xml file. Use a static shared thread-safe object (e.g. a semaphore or whatever) owned by my class that implements Job. I don't like the idea of using singletons via the static keyword under Tomcat/Quartz, not sure if there are side effects. Also I really don't want them to be true singletons, just something that is associated with a particular job definition. Implement my own Trigger which extends SimpleTrigger and contains shared state that could run its own TriggerListener. Again, I don't know how to setup the XML file to use this trigger rather than the standard <trigger><simple>...</simple></trigger>.

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• The MYSTERY SPIRAL

  - by CVS26

  Problem statement: Given a integer N, print N*N numbers in a N x N spiral Detailed problem description: http://2600hertz.wordpress.com/2010/03/20/the-mystery-spiral/ Solution: Recently posted the following code. (managed to compress it into as few as 99 lines...) //File : spiral.c // //INPUT : Size of spiral (N) //OUTPUT : Numbers printed in a N x N spiral #include <stdio.h> #include <conio.h> #include <stdlib.h> void main() { int N; clrscr(); //get input no. N printf("\nEnter size of Matrix: "); scanf("%d",&N); //Allocate reqd. memory int* matrix_ptr= (int*)malloc(N*N); //Filling the Matrix spirally int curr_val=N*N; int* curr_ptr=matrix_ptr; int curr_level=N; while(curr_level>1) { //curr_level-1 elements horizontally //from left to right for(int x=0;x<curr_level-1;x++) { *curr_ptr=curr_val; curr_val--; curr_ptr++; } //curr_level-1 elements vertically //from top to bottom for(int y=0;y<curr_level-1;y++) { *curr_ptr=curr_val; curr_val--; curr_ptr+=N; } //curr_level-1 elements horizontally //from right to left for(int z=0;z<curr_level-1;z++) { *curr_ptr=curr_val; curr_val--; curr_ptr--; } //curr_level-1 element vertically //from bottom to top for(int w=0;w<curr_level-1;w++) { *curr_ptr=curr_val; curr_val--; curr_ptr-=N; } //Next curr_ptr+=N+1; curr_level-=2; } *curr_ptr=curr_val; //routine to print the matrix printf("\n\n\n\n\n"); for( int i=0;i<N;i++) { for( int j=0;j<N;j++) { printf("%d\t",*(matrix_ptr+(i*N+j))); } printf("\n"); } getch(); } Please comment on further optimisations (if any)...

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• PyML 0.7.2 - How to prevent accuracy from dropping after storing/loading a classifier?

  - by Michael Aaron Safyan

  This is a followup from "Save PyML.classifiers.multi.OneAgainstRest(SVM()) object?". The solution to that question was close, but not quite right, (the SparseDataSet is broken, so attempting to save/load with that dataset container type will fail, no matter what. Also, PyML is inconsistent in terms of whether labels should be numbers or strings... it turns out that the oneAgainstRest function is actually not good enough, because the labels need to be strings and simultaneously convertible to floats, because there are places where it is assumed to be a string and elsewhere converted to float) and so after a great deal of hacking and such I was finally able to figure out a way to save and load my multi-class classifier without it blowing up with an error.... however, although it is no longer giving me an error message, it is still not quite right as the accuracy of the classifier drops significantly when it is saved and then reloaded (so I'm still missing a piece of the puzzle). I am currently using the following custom mutli-class classifier for training, saving, and loading: class SVM(object): def __init__(self,features_or_filename,labels=None,kernel=None): if isinstance(features_or_filename,str): filename=features_or_filename; if labels!=None: raise ValueError,"Labels must be None if loading from a file."; with open(os.path.join(filename,"uniquelabels.list"),"rb") as uniquelabelsfile: self.uniquelabels=sorted(list(set(pickle.load(uniquelabelsfile)))); self.labeltoindex={}; for idx,label in enumerate(self.uniquelabels): self.labeltoindex[label]=idx; self.classifiers=[]; for classidx, classname in enumerate(self.uniquelabels): self.classifiers.append(PyML.classifiers.svm.loadSVM(os.path.join(filename,str(classname)+".pyml.svm"),datasetClass = PyML.VectorDataSet)); else: features=features_or_filename; if labels==None: raise ValueError,"Labels must not be None when training."; self.uniquelabels=sorted(list(set(labels))); self.labeltoindex={}; for idx,label in enumerate(self.uniquelabels): self.labeltoindex[label]=idx; points = [[float(xij) for xij in xi] for xi in features]; self.classifiers=[PyML.SVM(kernel) for label in self.uniquelabels]; for i in xrange(len(self.uniquelabels)): currentlabel=self.uniquelabels[i]; currentlabels=['+1' if k==currentlabel else '-1' for k in labels]; currentdataset=PyML.VectorDataSet(points,L=currentlabels,positiveClass='+1'); self.classifiers[i].train(currentdataset,saveSpace=False); def accuracy(self,pts,labels): logger=logging.getLogger("ml"); correct=0; total=0; classindexes=[self.labeltoindex[label] for label in labels]; h=self.hypotheses(pts); for idx in xrange(len(pts)): if h[idx]==classindexes[idx]: logger.info("RIGHT: Actual \"%s\" == Predicted \"%s\"" %(self.uniquelabels[ classindexes[idx] ], self.uniquelabels[ h[idx] ])); correct+=1; else: logger.info("WRONG: Actual \"%s\" != Predicted \"%s\"" %(self.uniquelabels[ classindexes[idx] ], self.uniquelabels[ h[idx] ])) total+=1; return float(correct)/float(total); def prediction(self,pt): h=self.hypothesis(pt); if h!=None: return self.uniquelabels[h]; return h; def predictions(self,pts): h=self.hypotheses(self,pts); return [self.uniquelabels[x] if x!=None else None for x in h]; def hypothesis(self,pt): bestvalue=None; bestclass=None; dataset=PyML.VectorDataSet([pt]); for classidx, classifier in enumerate(self.classifiers): val=classifier.decisionFunc(dataset,0); if (bestvalue==None) or (val>bestvalue): bestvalue=val; bestclass=classidx; return bestclass; def hypotheses(self,pts): bestvalues=[None for pt in pts]; bestclasses=[None for pt in pts]; dataset=PyML.VectorDataSet(pts); for classidx, classifier in enumerate(self.classifiers): for ptidx in xrange(len(pts)): val=classifier.decisionFunc(dataset,ptidx); if (bestvalues[ptidx]==None) or (val>bestvalues[ptidx]): bestvalues[ptidx]=val; bestclasses[ptidx]=classidx; return bestclasses; def save(self,filename): if not os.path.exists(filename): os.makedirs(filename); with open(os.path.join(filename,"uniquelabels.list"),"wb") as uniquelabelsfile: pickle.dump(self.uniquelabels,uniquelabelsfile,pickle.HIGHEST_PROTOCOL); for classidx, classname in enumerate(self.uniquelabels): self.classifiers[classidx].save(os.path.join(filename,str(classname)+".pyml.svm")); I am using the latest version of PyML (0.7.2, although PyML.__version__ is 0.7.0). When I construct the classifier with a training dataset, the reported accuracy is ~0.87. When I then save it and reload it, the accuracy is less than 0.001. So, there is something here that I am clearly not persisting correctly, although what that may be is completely non-obvious to me. Would you happen to know what that is?

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• Problem in retrieving the ini file through web page

  - by MalarN

  Hi All, I am using an .ini file to store some values and retrieve values from it using the iniparser. When I give (hardcode) the query and retrive the value through the command line, I am able to retrive the ini file and do some operation. But when I pass the query through http, then I am getting an error (file not found), i.e., the ini file couldn't be loaded. Command line : int main(void) { printf("Content-type: text/html; charset=utf-8\n\n"); char* data = "/cgi-bin/set.cgi?pname=x&value=700&url=http://IP/home.html"; //perform some operation } Through http: .html function SetValue(id) { var val; var URL = window.location.href; if(id =="set") { document.location = "/cgi-bin/set.cgi?pname="+rwparams+"&value="+val+"&url="+URL; } } .c int * Value(char* pname) { dictionary * ini ; char *key1 = NULL; char *key2 =NULL; int i =0; int val; ini = iniparser_load("file.ini"); if(ini != NULL) { //key for fetching the value key1 = (char*)malloc(sizeof(char)*50); if(key1 != NULL) { strcpy(key1,"ValueList:"); key2 = (char*)malloc(sizeof(char)*50); if(key2 != NULL) { strcpy(key2,pname); strcat(key1,key2); val = iniparser_getint(ini, key1, -1); if(-1 == val || 0 > val) { return 0; } } else { //error free(key1); return; } } else { printf("ERROR : Memory Allocation Failure "); return; } } else { printf("ERROR : .ini File Missing"); return; } iniparser_freedict(ini); free(key1); free(key2); return (int *)val; } void get_Value(char* pname,char* value) { int result =0; result = Value(pname); printf("Result : %d",result); } int main(void) { printf("Content-type: text/html; charset=utf-8\n\n"); char* data = getenv("QUERY_STRING"); //char* data = "/cgi-bin/set.cgi?pname=x&value=700&url=http://10.50.25.40/home.html"; //Parse to get the values seperately as parameter name, parameter value, url //Calling get_Value method to set the value get_Value(final_para,final_val); } * file.ini * [ValueList] x = 100; y = 70; When the request is sent through html page, I am always getting .ini file missing. If directly the request is sent from C file them it works fine. How to resolve this?

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• Efficiency of data structures in C99 (possibly affected by endianness)

  - by Ninefingers

  Hi All, I have a couple of questions that are all inter-related. Basically, in the algorithm I am implementing a word w is defined as four bytes, so it can be contained whole in a uint32_t. However, during the operation of the algorithm I often need to access the various parts of the word. Now, I can do this in two ways: uint32_t w = 0x11223344; uint8_t a = (w & 0xff000000) >> 24; uint8_t b = (w & 0x00ff0000) >> 16; uint8_t b = (w & 0x0000ff00) >> 8; uint8_t d = (w & 0x000000ff); However, part of me thinks that isn't particularly efficient. I thought a better way would be to use union representation like so: typedef union { struct { uint8_t d; uint8_t c; uint8_t b; uint8_t a; }; uint32_t n; } word32; Using this method I can assign word32 w = 0x11223344; then I can access the various parts as I require (w.a=11 in little endian). However, at this stage I come up against endianness issues, namely, in big endian systems my struct is defined incorrectly so I need to re-order the word prior to it being passed in. This I can do without too much difficulty. My question is, then, is the first part (various bitwise ands and shifts) efficient compared to the implementation using a union? Is there any difference between the two generally? Which way should I go on a modern, x86_64 processor? Is endianness just a red herring here? I could inspect the assembly output of course, but my knowledge of compilers is not brilliant. I would have thought a union would be more efficient as it would essentially convert to memory offsets, like so: mov eax, [r9+8] Would a compiler realise that is what happening in the bit-shift case above? If it matters, I'm using C99, specifically my compiler is clang (llvm). Thanks in advance.

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• NSTimer as a self-targeting ivar.

  - by Matt Wilding

  I have come across an awkward situation where I would like to have a class with an NSTimer instance variable that repeatedly calls a method of the class as long as the class is alive. For illustration purposes, it might look like this: // .h @interface MyClock : NSObject { NSTimer* _myTimer; } - (void)timerTick; @end - // .m @implementation MyClock - (id)init { self = [super init]; if (self) { _myTimer = [[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(timerTick) userInfo:nil repeats:NO] retain]; } return self; } - (void)dealloc { [_myTimer invalidate]; [_myTImer release]; [super dealloc]; } - (void)timerTick { // Do something fantastic. } @end That's what I want. I don't want to to have to expose an interface on my class to start and stop the internal timer, I just want it to run while the class exists. Seems simple enough. But the problem is that NSTimer retains its target. That means that as long as that timer is active, it is keeping the class from being dealloc'd by normal memory management methods because the timer has retained it. Manually adjusting the retain count is out of the question. This behavior of NSTimer seems like it would make it difficult to ever have a repeating timer as an ivar, because I can't think of a time when an ivar should retain its owning class. This leaves me with the unpleasant duty of coming up with some method of providing an interface on MyClock that allows users of the class to control when the timer is started and stopped. Besides adding unneeded complexity, this is annoying because having one owner of an instance of the class invalidate the timer could step on the toes of another owner who is counting on it to keep running. I could implement my own pseudo-retain-count-system for keeping the timer running but, ...seriously? This is way to much work for such a simple concept. Any solution I can think of feels hacky. I ended up writing a wrapper for NSTimer that behaves exactly like a normal NSTimer, but doesn't retain its target. I don't like it, and I would appreciate any insight.

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• C# UDP decoding datagrams fails randomly

  - by Tom Frey

  Hi, I'm experiencing an issue in a multi threaded application and have been debugging it for the last 3 days but for the life of it can not figure it out. I'm writing this, hoping that I either have a DUH moment when typing this or somebody sees something obvious in the code snippets I provide. Here's what's going on: I've been working on a new UDP networking library and have a data producer that multicasts UDP datagrams to several receiver applications. The sender sends on two different sockets that are bound to separate UDP multicast addresses and separate ports. The receiver application also creates two sockets and binds each one to one of the sender's multicast address/port. When the receiver receives the datagram, it copies it from the the buffer in a MemoryStream which is then put onto a thread safe queue, where another thread reads from it and decodes the data out of the MemoryStream. Both sockets have their own queues. What happens now is really weird, it happens randomly, non-reproducible and when I run multiple receiver applications, it only happens randomly on one of them every now and then. Basically, the thread that reads the MemoryStream out of the queue, reads it via a BinaryReader like ReadInt32(), etc. and thereby decodes the data. Every now and then however when it reads the data, the data it reads from it is incorrect, e.g. a negative integer number which the sender never would encode. However, as mentioned before, the decoding only fails in one of the receiver applications, in the other ones the datagram decodes fine. Now you might be saying, well, probably the UDP datagram has a byte corruption or something but I've logged every single datagram that's coming in and compared them on all receivers and the datagrams every application receives are absolutely identical. Now it gets even weirder, when I dump the datagram that failed to decode to disk and write a unit test that reads it and runs it through the decoder, it decodes just fine. Also when I wrap a try/catch around the decoder, reset the MemoryStream position in the catch and run it through the decoder again, it decodes just fine. To make it even weirder, this also only happens when I bind both sockets to read data from the sender, if I only bind one, it doesn't happen or at least I wasn't able to reproduce it. Here are is some corresponding code to what's going on: This is the receive callback for the socket: private void ReceiveCompleted(object sender, SocketAsyncEventArgs args) { if (args.SocketError != SocketError.Success) { InternalShutdown(args.SocketError); return; } if (args.BytesTransferred > SequencedUnitHeader.UNIT_HEADER_SIZE) { DataChunk chunk = new DataChunk(args.BytesTransferred); Buffer.BlockCopy(args.Buffer, 0, chunk.Buffer, 0, args.BytesTransferred); chunk.MemoryStream = new MemoryStream(chunk.Buffer); chunk.BinaryReader = new BinaryReader(chunk.MemoryStream); chunk.SequencedUnitHeader.SequenceID = chunk.BinaryReader.ReadUInt32(); chunk.SequencedUnitHeader.Count = chunk.BinaryReader.ReadByte(); if (prevSequenceID + 1 != chunk.SequencedUnitHeader.SequenceID) { log.Error("UdpDatagramGap\tName:{0}\tExpected:{1}\tReceived:{2}", unitName, prevSequenceID + 1, chunk.SequencedUnitHeader.SequenceID); } else if (chunk.SequencedUnitHeader.SequenceID < prevSequenceID) { log.Error("UdpOutOfSequence\tName:{0}\tExpected:{1}\tReceived:{2}", unitName, prevSequenceID + 1, chunk.SequencedUnitHeader.SequenceID); } prevSequenceID = chunk.SequencedUnitHeader.SequenceID; messagePump.Produce(chunk); } else UdpStatistics.FramesRxDiscarded++; Socket.InvokeAsyncMethod(Socket.ReceiveAsync, ReceiveCompleted, asyncReceiveArgs); } Here's some stub code that decodes the data: public static void OnDataChunk(DataChunk dataChunk) { try { for (int i = 0; i < dataChunk.SequencedUnitHeader.Count; i++) { int val = dataChunk.BinaryReader.ReadInt32(); if(val < 0) throw new Exception("EncodingException"); // do something with that value } } catch (Exception ex) { writer.WriteLine("ID:" + dataChunk.SequencedUnitHeader.SequenceID + " Count:" + dataChunk.SequencedUnitHeader.Count + " " + BitConverter.ToString(dataChunk.Buffer, 0, dataChunk.Size)); writer.Flush(); log.ErrorException("OnDataChunk", ex); log.Info("RETRY FRAME:{0} Data:{1}", dataChunk.SequencedUnitHeader.SequenceID, BitConverter.ToString(dataChunk.Buffer, 0, dataChunk.Size)); dataChunk.MemoryStream.Position = 0; dataChunk.SequencedUnitHeader.SequenceID = dataChunk.BinaryReader.ReadUInt32(); dataChunk.SequencedUnitHeader.Count = dataChunk.BinaryReader.ReadByte(); OnDataChunk(dataChunk); } } You see in the catch{} part I simply reset the MemoryStream.Position to 0 and call the same method again and it works just fine that next time? I'm really out of ideas at this point and unfortunately had no DUH moment writing this. Anybody have any kind of idea what might be going on or what else I could do to troubleshoot this? Thanks, Tom

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