Weird crash in NSURLConnectionLoader thread

Question

We started seeing crashes that happen when our app starts. I wasn't able to reproduce it, and it happens only to a few users.

The exception is: Exception Type: EXC_BAD_ACCESS Code: KERN_INVALID_ADDRESS at 0x3250974659

The crash happened in a thread named com.apple.NSURLConnectionLoader when calling -[NSBlockOperation main]

This is the stack trace of that thread:

0    libobjc.A.dylib     objc_msgSend + 9
1    Foundation      -[NSBlockOperation main] + 200
2    Foundation  -[__NSOperationInternal start] + 840
3    Foundation  -[_NSCFURLProtocolBridgeWithTrampoline processEventQ] + 344
4    Foundation  -[_NSCFURLProtocolBridgeWithTrampoline pushEvent:from:] + 298
5    Foundation  -[_NSCFURLProtocolBridge stop] + 88
6    Foundation  _bridger + 64
7    CFNetwork   __block_global_7 + 24
8    CFNetwork   __block_global_8 + 12
9    CFNetwork   ___performAsync_block_invoke_068 + 18
10   CoreFoundation  CFArrayApplyFunction + 176
11   CFNetwork   RunloopBlockContext::perform() + 74
12   CFNetwork   MultiplexerSource::perform() + 188
13   CoreFoundation  __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 14
14   CoreFoundation  __CFRunLoopDoSources0 + 212
15   CoreFoundation  __CFRunLoopRun + 646
16   CoreFoundation  CFRunLoopRunSpecific + 356
17   CoreFoundation  CFRunLoopRunInMode + 104
18   Foundation  +[NSURLConnection(Loader) _resourceLoadLoop:] + 308
19   Foundation  __NSThread__main__ + 972
20   libsystem_c.dylib   _pthread_start + 308

Would appreciate any help to understand what's can cause this kind of crash.

Answer 1

With me this code indirectly is causing the crash. If I read the crash dump correctly

[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error]

is triggering the NSURLConnectionLoaderThread. This is probably what they use for Asynchronous support. But as I use synchronous request, there is no way I can deallocate an object while the thread is running. If you ask me, that is a bug in IOS 7.

NSMutableURLRequest* request = [self setupRequestWithService:service andMethod:operation];

    [request addValue:CONTENT_TYPE_APPLICATION_JSON forHTTPHeaderField:REQUEST_HEADER_CONTENT_TYPE];
    [request setHTTPMethod:@"POST"];

    NSError* error = nil;
    NSData* jsonData = nil;

    NSAssert(message,@"Message must not be null");

    jsonData = [NSJSONSerialization dataWithJSONObject:[message toDictionary] options:kNilOptions error:&error];

    NSAssert(! error, @"Message could not be json serialized");

    Log(@"----------------------------------------------------------------------");
    Log(@"JSON DATA: - %@", [[NSString alloc] initWithData:jsonData
                                                     encoding:NSUTF8StringEncoding]);
    Log(@"----------------------------------------------------------------------");

    [request setHTTPBody:jsonData];

    // Send Synchronous Request
    NSURLResponse *response = nil;
    error = nil;
    NSData* responseData = nil;
    NSString* responseString = nil;

    responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

Answer 2

My guess (because without code all answers will be guessing) - is you're deallocating objects you are using in blocks before blocks executes.

Paste a code so we can help more.