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AWS SDK for iOS. For more information, see our web site:
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Crash in [AWSMQTTSession drainSenderQueue] #1071

Closed wxsdmy closed 5 years ago

wxsdmy commented 6 years ago

2018/10/24 12:22:39:926 -------- Exception -------- reson: NSRangeException Exception name：*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array Exception stack：( 0 CoreFoundation 0x0000000184727f10 + 252 1 libobjc.A.dylib 0x00000001838f5a40 objc_exception_throw + 56 2 CoreFoundation 0x000000018469d85c _CFArgv + 0 3 CoreFoundation 0x000000018460dba8 + 188 4 AWSIoT 0x0000000102780d78 -[AWSMQTTSession drainSenderQueue] + 372 5 AWSIoT 0x0000000102780868 -[AWSMQTTSession send:] + 100 6 AWSIoT 0x000000010277d7b4 -[AWSMQTTSession subscribeToTopic:atLevel:] + 264 7 AWSIoT 0x000000010277a77c -[AWSIoTMQTTClient session:handleEvent:] + 948 8 AWSIoT 0x000000010277efe4 -[AWSMQTTSession decoder:newMessage:] + 1172 9 AWSIoT 0x00000001027c44b0 -[AWSMQTTDecoder stream:handleEvent:] + 1428 10 CoreFoundation 0x00000001846c941c + 216 11 CoreFoundation 0x00000001846c8a08 + 372 12 CoreFoundation 0x00000001846b65b8 + 24 13 CoreFoundation 0x00000001846b6538 + 88 14 CoreFoundation 0x00000001846b5e1c + 176 15 CoreFoundation 0x00000001846b0ce8 + 1040 16 CoreFoundation 0x00000001846b05b8 CFRunLoopRunSpecific + 436 17 Foundation 0x00000001850a46a4 + 300 18 AWSIoT 0x0000000102778ef8 -[AWSIoTMQTTClient openStreams:] + 676 19 Foundation 0x00000001851d73b0 + 1040 20 libsystem_pthread.dylib 0x00000001843412fc + 128 21 libsystem_pthread.dylib 0x000000018434125c _pthread_start + 48 22 libsystem_pthread.dylib 0x0000000184344d08 thread_start + 4 )

SDK Version: 2.6.32

bhavinmdesai commented 6 years ago

I am also having similar kind of exception for my live app users. It has happened sometime to our internal test users as well but we don't have exact steps to reproduce. Here is my stacktrace:

Fatal Exception: NSRangeException
0  CoreFoundation                 0x1d1a0fef8 __exceptionPreprocess
1  libobjc.A.dylib                0x1d0bdda40 objc_exception_throw
2  CoreFoundation                 0x1d198585c _CFArgv
3  CoreFoundation                 0x1d18f5ba8 -[__NSArrayM objectAtIndex:]
4  Rewardle                       0x10319c4ec -[AWSMQTTSession drainSenderQueue] (AWSMQTTSession.m:672)
5  Rewardle                       0x10319bfdc -[AWSMQTTSession send:] (AWSMQTTSession.m:646)
6  Rewardle                       0x103198f28 -[AWSMQTTSession subscribeToTopic:atLevel:] (AWSMQTTSession.m:167)
7  Rewardle                       0x1031800dc -[AWSIoTMQTTClient subscribeToTopic:qos:messageCallback:ackCallback:] (AWSIoTMQTTClient.m:767)
8  Rewardle                       0x10317fe78 -[AWSIoTMQTTClient subscribeToTopic:qos:messageCallback:] (AWSIoTMQTTClient.m:741)
9  Rewardle                       0x1031520f0 -[AWSIoTDataManager subscribeToTopic:QoS:messageCallback:] (AWSIoTDataManager.m:528)
10 Rewardle                       0x10300d424 -[RealTimeFeedCall subscriptionCall] (RealTimeFeedCall.m:194)
11 Rewardle                       0x10317f01c __42-[AWSIoTMQTTClient notifyConnectionStatus]_block_invoke (AWSIoTMQTTClient.m:580)
12 libdispatch.dylib              0x1d14476c8 _dispatch_call_block_and_release
13 libdispatch.dylib              0x1d1448484 _dispatch_client_callout
14 libdispatch.dylib              0x1d13f7b94 _dispatch_root_queue_drain
15 libdispatch.dylib              0x1d13f8308 _dispatch_worker_thread2
16 libsystem_pthread.dylib        0x1d162a190 _pthread_wqthread
17 libsystem_pthread.dylib        0x1d162cd00 start_wqthread
mutablealligator commented 6 years ago

Hi @wxsdmy @bhavinmdesai

Looking at the drainSenderQueue implementation, https://github.com/aws/aws-sdk-ios/blob/master/AWSIoT/Internal/MQTTSDK/AWSM... we remove the object from the queue until the queue is empty. I see two callers to this method 1) sending a message 2) the timer handler. In addition to this the encoder dequeues the element at the front of the queue: "- (void)encoder:(AWSMQTTEncoder*)sender handleEvent:(AWSMQTTEncoderEvent) eventCode" when the mqtt connection is established in order to encode the message. It is possible that there is a race between these three potential callers which try to mutate the queue without proper synchronization. Continuing my root-cause.

Would it be possible to share a sample app or code snippet where you use the IoT SDK?

scb01 commented 5 years ago

@wxsdmy @bhavinmdesai

The latest rev of the iOS SDK (2.6.34) contains a fix for this issue. Can you update to the latest rev and let us know how it goes?

scb01 commented 5 years ago

@wxsdmy @bhavinmdesai

Closing this issue as I haven't heard back. Please feel free to reopen if the error is still occurring.