Due to the fact that the client cannot implement just a few downloads on its server in a short time, and backgroundDownloadTaks were very incompatible when there are so many files (500-1000 downloads), I decided to use NSURLDownloadTask without a background NSURLSession.
It works great with a lot of files, but there are inconveniences. Memory usage always increases until I get a memory warning. When I receive it, I cancel pending tasks and free NSURLCache, but the memory is not released, so when you resume downloading, you get the same memory warning.
I do not use cancelWithResumeData to cancel tasks.
This is my code.
- (void) startDownloadFiles:(NSMutableArray*)arrayFiles { if([[UIDevice currentDevice] isMultitaskingSupported]) { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ if (!self.session) { NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration]; sessionConfiguration.HTTPMaximumConnectionsPerHost = 5; sessionConfiguration.timeoutIntervalForRequest = 0; sessionConfiguration.timeoutIntervalForResource = 0; sessionConfiguration.requestCachePolicy = NSURLCacheStorageNotAllowed; self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:nil]; } //Resetting session [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) { for (NSURLSessionTask *_task in downloadTasks) { [_task cancel]; } [self.session resetWithCompletionHandler:^{ for (id<FFDownloadFileProtocol> file in self.selectedCatalogProducto.downloadInfo.arrayFiles) { if (cancel) break; //Do not create more taks if (![file isDownloaded]) [self startDownloadFile:file]; } }]; }]; }); } } - (void) startDownloadFile:(id<FFDownloadFileProtocol>)file { if (![file isDownloading]) { if ([file taskIdentifier] == -1 && ! cancel) { NSURLSessionDownloadTask *task = [self.session downloadTaskWithURL:[file downloadSource]]; if (task) { [file setDownloadTask:task]; [file setTaskIdentifier:[file downloadTask].taskIdentifier]; [[file downloadTask] resume]; } else { NSLog(@"Error creando tarea para descargar %@", [file downloadSource]); } } } } #pragma mark - Auxiliar Methods -(id<FFDownloadFileProtocol>)getFileDownloadInfoIndexWithTaskIdentifier:(unsigned long)taskIdentifier { for (id<FFDownloadFileProtocol> file in self.selectedCatalogProducto.downloadInfo.arrayFiles) { if (file.taskIdentifier == taskIdentifier) { return file; } } return nil; } #pragma mark - NSURLSessionDownloadTaskDelegate - (void) URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) { NSLog(@"Unknown transfer size"); } else { // Locate the FileDownloadInfo object among all based on the taskIdentifier property of the task. id<FFDownloadFileProtocol> file = [self getFileDownloadInfoIndexWithTaskIdentifier:downloadTask.taskIdentifier]; // Calculate the progress. file.downloadProgress = (double)totalBytesWritten / (double)totalBytesExpectedToWrite; // [[NSOperationQueue mainQueue] addOperationWithBlock:^{ // NSLog("%@ ; %f", [file fileName], [file downloadProgress]); // }]; } } - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location { id<FFDownloadFileProtocol> file = [self getFileDownloadInfoIndexWithTaskIdentifier:downloadTask.taskIdentifier]; if (file) { NSError *error; NSFileManager *fileManager = [NSFileManager defaultManager]; NSURL *destinationURL = [[NSURL fileURLWithPath:tempPath] URLByAppendingPathComponent:[file fileName]]; if ([fileManager fileExistsAtPath:[destinationURL path]]) { NSError *delError = nil; [fileManager removeItemAtURL:destinationURL error:nil]; if (delError) { NSLog(@"Error borrando archivo temporal en %@", [destinationURL path]); } } BOOL success = [fileManager copyItemAtURL:location toURL:destinationURL error:&error]; if (success) { // Change the flag values of the respective FileDownloadInfo object. file.isDownloading = NO; file.isDownloaded = YES; // Set the initial value to the taskIdentifier property of the file object, // so when the start button gets tapped again to start over the file download. } else { NSLog(@"Unable to copy temp file to %@ Error: %@", [destinationURL path], [error localizedDescription]); } if ([[UIApplication sharedApplication] applicationState] == UIApplicationStateActive) { indexFile++; [[NSOperationQueue mainQueue] addOperationWithBlock:^{ [self numFilesDownloaded:indexFile]; }]; } } } - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error { id<FFDownloadFileProtocol> file = [self getFileDownloadInfoIndexWithTaskIdentifier:task.taskIdentifier]; if (error != nil && error.code != -999) { //No se ha producido error o se ha cancelado la tarea bajo demanda [[NSOperationQueue mainQueue] addOperationWithBlock:^{ NSLog(@"Download: %@. \n Downlonad completed with error: %@", [task.response.URL absoluteString], [error localizedDescription]); if (!cancel) { NSString *alertBody = @"Se ha producido un error en la descarga, por favor reanúdela manualmente"; if ([error.domain isEqualToString:@"NSPOSIXErrorDomain"] && (error.code == 1) ) { alertBody = @"Se ha interrumpido la descarga debido a que su iPad está bloqueado por código. Por favor reanude la descarga manualmente y evite que el iPad se bloquee"; } // Show a local notification when all downloads are over. UILocalNotification *localNotification = [[UILocalNotification alloc] init]; localNotification.alertBody = alertBody; [[UIApplication sharedApplication] presentLocalNotificationNow:localNotification]; [self errorDownloading:error.localizedDescription]; } }]; } else if (file) { NSLog(@"%@ download finished successfully.", [[file downloadSource] absoluteString]); file.taskIdentifier = -1; // In case there is any resume data stored in the file object, just make it nil. file.taskResumeData = nil; file.downloadTask = nil; } else if (cancel) { NSLog(@"Tarea cancelada"); } if (self.selectedCatalogProducto.downloadInfo.arrayFiles.count == indexFile && !cancel) { [[NSOperationQueue mainQueue] addOperationWithBlock:^{ if (!complete) { complete = YES; [self downloadComplete]; } }]; } task = nil; } #pragma mark - Memory warning - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; if (_isDownloading) { [self storeCatalogProductInfo:self.selectedCatalogProducto andDownloadInfo:YES]; [self stopDownloading]; } [[NSURLCache sharedURLCache] removeAllCachedResponses]; [self.session.configuration.URLCache removeAllCachedResponses]; }
And these are two snapshots of memory usage
Memory usage increases when downloading files
Task loading stopped but memory not released
Why can't I free my memory?
Thanks for the help provided.