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PONSURLConnection sendAsynchronousRequest never free up the memory
 

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    <p>I am working on an iOS app which dispatch quite a number of tasks to my serial queue. The task is to download images from my web server, save it to disk, and later displayed on <code>UIImageView</code>. However, <code>[NSURLConnection sendAsynchrousRequest]</code> will keep eating up more and more memory until iOS kill my process.</p> <p>The downloader method looks like this:</p> <pre><code>// dispatch_queue_t is created once by: m_pRequestQueue = dispatch_queue_create( "mynamespace.app", DISPATCH_QUEUE_SERIAL); - (void) downloadImageInBackgroundWithURL:(NSString*) szUrl { __block typeof(self) bSelf = self; __block typeof(m_pUrlRequestQueue) bpUrlRequestQueue = m_pRequestQueue; dispatch_async( m_pRequestQueue, ^{ NSAutoreleasePool *pAutoreleasePool = [[NSAutoreleasePool alloc] init]; NSURLRequest *pRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:szUrl] cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:URL_REQUEST_TIMEOUT]; [NSURLConnection sendAsynchronousRequest:pRequest queue:bpUrlRequestQueue completionHandler:^(NSURLResponse *pResponse, NSData *pData, NSError *pError) { NSAutoreleasePool *pPool = [[NSAutoreleasePool alloc] init]; if ( pError != nil ) { } else { // convert image to png format UIImage *pImg = [UIImage imageWithData:pData]; NSData *pDataPng = UIImagePNGRepresentation(pImg); bool bSaved = [[NSFileManager defaultManager] createFileAtPath:szCacheFile contents:pDataPng attributes:nil]; } __block typeof(pDataPng) bpDataPng = pDataPng; __block typeof(pError) bpError = pError; dispatch_sync( dispatch_get_main_queue(), ^ { NSAutoreleasePool *autoreleasepool = [[NSAutoreleasePool alloc] init]; UIImage *pImage = [[UIImage alloc] initWithData:bpDataPng]; // display the image [pImage release]; // NSLog( @"image retain count: %d", [pImage retainCount] ); // 0, bad access [autoreleasepool drain]; }); } [pPool drain]; }]; // end sendAsynchronousRequest [pAutoreleasePool drain]; }); // end dispatch_async } // end downloadImageInBackgroundWithURL </code></pre> <p>I am quite sure it is something inside <code>[NSURLConnection sendAsynchronousRequest]</code> as the profiler is showing that the function is the one eating up all the memory...</p> <p>However, I am also not very sure about the dispatch_*** and block things, I've always used C and C++ code with pthread before, but after reading from Apple's documentation on migrating away from thread, I decided to give GCD a try, objective-c is so troublesome and I'm not sure how to release the <code>NSData *pData</code> and <code>NSURLResponse *pResponse</code> as it crash whenever I do it.</p> <p>Please advice... really need help to learn and appreciate objective-c...</p> <p><img src="https://i.stack.imgur.com/sQxIg.png" alt="Profiler"></p> <p><strong>ADDITIONAL EDIT:</strong></p> <p>Thanks to @robhayward, I put the pImg and pDataPng outside as __block variable, use his RHCacheImageView way of downloading data ( NSData initWithContentOfURL )</p> <p>Thanks as well to @JorisKluivers, the first UIImage can actually be reused to display as UIImageView recognized both jpg and png format, just my later processing requires png format and I am reading from the disk later just when required</p>
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