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POCore Data crashing when doing count request using performBlock
 

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  1. POCore Data crashing when doing count request using performBlock
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    <p>My iOS app is crashing when doing two calls to countForFetchRequest at the same time on the same private queue NSManagedObjectContext using performBlock.</p> <p>I setup my childContext like this</p> <pre><code>_childContext = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType]; [_childContext setParentContext:self.managedObjectContext]; </code></pre> <p>And this is my performBlock that calls countForFetchRequest</p> <pre><code>[self.childContext performBlock:^{ NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"History"]; fetchRequest.predicate = [NSPredicate predicateWithFormat:@"url == %@", url]; NSError *error = nil; NSUInteger num = [self.childContext countForFetchRequest:fetchRequest error:&amp;error]; if(error != nil){ NSLog(@"Error getting count for history url %@ %@", url, error); return; } if(num &gt; 0){ // Already have this in the history, don't re-add it return; } History *history = (History *)[NSEntityDescription insertNewObjectForEntityForName:@"History" inManagedObjectContext:self.childContext]; history.url = url; history.title = title; if(![self.childContext save:&amp;error]){ NSLog(@"Error occurred saving history item %@ %@ %@", title, url, error); } }]; </code></pre> <p>And here is the crash log:</p> <pre><code>Thread 0 name: Dispatch queue: com.apple.main-thread Thread 0 Crashed: 0 libsystem_kernel.dylib 0x3a427350 __pthread_kill + 8 1 libsystem_c.dylib 0x3a39e11e pthread_kill + 54 2 libsystem_c.dylib 0x3a3da96e abort + 90 3 libc++abi.dylib 0x39978d4a abort_message + 70 4 libc++abi.dylib 0x39975ff4 default_terminate() + 20 5 libobjc.A.dylib 0x39f29a74 _objc_terminate() + 144 6 libc++abi.dylib 0x39976078 safe_handler_caller(void (*)()) + 76 7 libc++abi.dylib 0x39976110 std::terminate() + 16 8 libc++abi.dylib 0x39977594 __cxa_rethrow + 84 9 libobjc.A.dylib 0x39f299cc objc_exception_rethrow + 8 10 CoreData 0x31e868e0 -[NSManagedObjectContext(_NSInternalAdditions) _countWithNoChangesForRequest:error:] + 764 11 CoreData 0x31e833fe -[NSManagedObjectContext countForFetchRequest:error:] + 1062 12 CoreData 0x31e92470 __82-[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:]_block_invoke_0 + 460 13 libdispatch.dylib 0x3a345d26 _dispatch_barrier_sync_f_slow_invoke + 82 14 libdispatch.dylib 0x3a3404b4 _dispatch_client_callout + 20 15 libdispatch.dylib 0x3a3451b8 _dispatch_main_queue_callback_4CF$VARIANT$mp + 220 16 CoreFoundation 0x3205cf36 __CFRunLoopRun + 1286 17 CoreFoundation 0x31fcfeb8 CFRunLoopRunSpecific + 352 18 CoreFoundation 0x31fcfd44 CFRunLoopRunInMode + 100 19 GraphicsServices 0x35b992e6 GSEventRunModal + 70 20 UIKit 0x33ee52fc UIApplicationMain + 1116 21 Accountable2You Mobile 0x000e5d28 0xe4000 + 7464 22 Accountable2You Mobile 0x000e5cc4 0xe4000 + 7364 Thread 1 name: Dispatch queue: NSManagedObjectContext Queue Thread 1: 0 libsystem_kernel.dylib 0x3a416f04 semaphore_wait_trap + 8 1 libdispatch.dylib 0x3a3462fc _dispatch_thread_semaphore_wait$VARIANT$mp + 8 2 libdispatch.dylib 0x3a34487c _dispatch_barrier_sync_f_slow + 96 3 CoreData 0x31e82df2 _perform + 166 4 CoreData 0x31e921c6 -[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:] + 238 5 CoreData 0x31e86770 -[NSManagedObjectContext(_NSInternalAdditions) _countWithNoChangesForRequest:error:] + 396 6 CoreData 0x31e833fe -[NSManagedObjectContext countForFetchRequest:error:] + 1062 7 Accountable2You Mobile 0x000ee7be 0xe4000 + 42942 8 CoreData 0x31e86072 developerSubmittedBlockToNSManagedObjectContextPerform_privateasync + 66 9 libdispatch.dylib 0x3a344eca _dispatch_queue_drain$VARIANT$mp + 138 10 libdispatch.dylib 0x3a344dbc _dispatch_queue_invoke$VARIANT$mp + 36 11 libdispatch.dylib 0x3a34591a _dispatch_root_queue_drain + 182 12 libdispatch.dylib 0x3a345abc _dispatch_worker_thread2 + 80 13 libsystem_c.dylib 0x3a375a0e _pthread_wqthread + 358 14 libsystem_c.dylib 0x3a3758a0 start_wqthread + 4 </code></pre> <p>Am I using the performBlock correctly?</p> <p><strong>Edit: More details</strong></p> <p>The performBlock is being called in a webViewDidFinishLoad:webView delegate method. I have multiple UIWebViews and when they finish loading they are calling the delegate method which is in turn calling the performBlock to see if it needs to add the url to the core data database.</p>
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    1. USAustin
    1. USAustin
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      1. VTUpMod
    1. COsounds like - from the title - that the crash line countForFetchRequest? Could you try without the threading (on the main) to rule out other issues with the query?
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      1. USdanh
    2. COShow how you are calling this twice on the same thread.
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      1. USMundi
    3. CO@Mundi I edited the question to include some additional information about how it is being called.
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      1. USAustin
 

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