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POsetKeepAliveTimeout and BackgroundTasks
 

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  1. POsetKeepAliveTimeout and BackgroundTasks
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    <p>I've a big headache with the topic. I'm working on an application that needs to poll a webserver regularly, in order to check for new data. Based on the returned information, I wish to push a local notification to the user.</p> <p>I know that this approach is slightly different from the one depicted by Apple, in which a remote server makes the work, pushing a remote notification, based on APNS. However, there are many reasons for which i cannot take this approach in consideration. One for all, is the user authentication mechanism. The remote server, for security reasons, cannot take into account the user credentials. All that i can do is to move the login and fetching core, to the client (iPhone).</p> <p>I noticed that Apple offers an opportunity for applications to wake-up and keep opened a Socket connection (ie. a VoIP application). </p> <p>So, I started investigate in this way. Added the required information in the plist, I'm able to "wake" my application, using something like this in my appDelegate:</p> <pre><code>[[UIApplication sharedApplication] setKeepAliveTimeout:1200 handler:^{ NSLog(@"startingKeepAliveTimeout"); [self contentViewLog:@"startingKeepAliveTimeout"]; MyPushOperation *op = [[MyPushOperation alloc] initWithNotificationFlag:0 andDataSource:nil]; [queue addOperation:op]; [op release]; }]; </code></pre> <p>The NSOperation, then starts a background task using the following block code:</p> <pre><code>#pragma mark SyncRequests -(void) main { NSLog(@"startSyncRequest"); [self contentViewLog:@"startSyncRequest"]; bgTask = [app beginBackgroundTaskWithExpirationHandler:^{ NSLog(@"exipiration handler triggered"); [app endBackgroundTask:bgTask]; bgTask = UIBackgroundTaskInvalid; [self cancel]; }]; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSMutableURLRequest *anURLRequest; NSURLResponse *outResponse; NSError *exitError; NSString *username; NSString *password; NSLog(@"FirstLogin"); anURLRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:webserverLogin, username, password]]]; [anURLRequest setHTTPMethod:@"GET"]; [anURLRequest setTimeoutInterval:120.00]; [anURLRequest setCachePolicy:NSURLRequestReloadIgnoringCacheData]; exitError = nil; NSData *tmpData = [NSURLConnection sendSynchronousRequest:anURLRequest returningResponse:&amp;outResponse error:&amp;exitError]; [anURLRequest setTimeoutInterval:120.00]; if(exitError != nil) { //somethings goes wrong NSLog(@"somethings goes wrong"); [app endBackgroundTask:bgTask]; bgTask = UIBackgroundTaskInvalid; [self cancel]; return; } //do some stuff with NSData and prompt the user with a UILocalNotification NSLog(@"AlltasksCompleted"); [app endBackgroundTask:bgTask]; bgTask = UIBackgroundTaskInvalid; [self cancel]; }); } } </code></pre> <p>The above code seems to work (sometimes), but many other it crashes my application, with the following log information:</p> <pre><code>Exception Type: 00000020 Exception Codes: 0x8badf00d Highlighted Thread: 3 Application Specific Information: DemoBackApp[5977] has active assertions beyond permitted time: {( &lt;SBProcessAssertion: 0xa9da0b0&gt; identifier: UIKitBackgroundCompletionTask process: DemoBackApp[5977] permittedBackgroundDuration: 600.000000 reason: finishTask owner pid:5977 preventSuspend preventIdleSleep )} Elapsed total CPU time (seconds): 0.010 (user 0.010, system 0.000), 100% CPU Elapsed application CPU time (seconds): 0.000, 0% CPU </code></pre> <p>For ones who ask, yes. I've tried the Async NSURLConnection approach, too. No matter. It crash the same, even if I use an async approach with timeout handler and didFinishLoading:WithError.</p> <p>I'm stuck. Any hints are high appreciated.</p>
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