Hi i have a Problem with this Library: LTSupportAutomotive
I´m a swift programmer so not really good in objective c.
how to fix this race condition?
I hope someone can help me.
'*** -[__NSArrayM insertObject:atIndex:]: index 1 beyond bounds for empty array'
-(void)asyncEnqueueInternalCommand:(LTOBD2AdapterInternalCommand*)internalCommand
{
@synchronized(self) {
[_commandQueue addObject:internalCommand];
}
}
Source code:
UPDATE 1:
Created a branch with the first fixes: https://github.com/Skyb0rg/LTSupportAutomotive/tree/BugfixMemoryManagement
After adding additional commandQueue i got new errors:
in LTBTLEWriteCharacteristicStream.m
-(void)characteristicDidWriteValue
{
[self.delegate stream:self handleEvent:NSStreamEventHasSpaceAvailable];
}
this function is crashing with: Selector name found in current argument registers: delegate
Thread 6 Crashed: 0 libobjc.A.dylib 0x00000001bcc19430 objc_retain + 16
1 LTSupportAutomotive 0x00000001093c2a34 -[LTBTLEWriteCharacteristicStream characteristicDidWriteValue] (LTBTLEWriteCharacteristicStream.m:39)
2 LTSupportAutomotive 0x00000001093c2714 -[LTBTLESerialTransporter peripheral:didWriteValueForCharacteristic:error:] (LTBTLESerialTransporter.m:311)
3 CoreBluetooth 0x00000001c35e6ce0 -[CBPeripheral handleAttributeEvent:args:attributeSelector:delegateSelector:delegateFlag:] + 236
4 CoreBluetooth 0x00000001c35e6e40 -[CBPeripheral handleCharacteristicEvent:characteristicSelector:delegateSelector:delegateFlag:] + 128
5 CoreBluetooth 0x00000001c35e24f0 -[CBPeripheral handleMsg:args:] + 352
6 CoreBluetooth 0x00000001c35dcbfc -[CBCentralManager handleMsg:args:] + 200
7 CoreBluetooth 0x00000001c35eb770 __30-[CBXpcConnection _handleMsg:]_block_invoke + 56
8 libdispatch.dylib 0x00000001bd4696c8 _dispatch_call_block_and_release + 20
9 libdispatch.dylib 0x00000001bd46a484 _dispatch_client_callout + 12
10 libdispatch.dylib 0x00000001bd411bd0 _dispatch_lane_serial_drain$VARIANT$mp + 588
11 libdispatch.dylib 0x00000001bd41274c _dispatch_lane_invoke$VARIANT$mp + 480
12 libdispatch.dylib 0x00000001bd411a9c _dispatch_lane_serial_drain$VARIANT$mp + 280
13 libdispatch.dylib 0x00000001bd412718 _dispatch_lane_invoke$VARIANT$mp + 428
14 libdispatch.dylib 0x00000001bd41aeb8 _dispatch_workloop_worker_thread + 596
15 libsystem_pthread.dylib 0x00000001bd64d0dc _pthread_wqthread + 308
16 libsystem_pthread.dylib 0x00000001bd64fcec start_wqthread + 0
and another crash in: LTBTLEReadCharacteristicStream.m
-(void)characteristicDidUpdateValue
{
NSData* value = _characteristic.value;
[_buffer appendData:value];
[self.delegate stream:self handleEvent:NSStreamEventHasBytesAvailable];
}
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[OS_dispatch_data stream:handleEvent:]: unrecognized selector sent to instance 0x281be1b90'
Thread 9 Crashed: 0 libsystem_kernel.dylib 0x00000001bd5c7104 __pthread_kill + 8
1 libsystem_pthread.dylib 0x00000001bd643020 pthread_kill$VARIANT$mp + 376
2 libsystem_c.dylib 0x00000001bd51ed78 abort + 136
3 VW-R-CLUB Member APP 0x00000001045603ac uncaught_exception_handler + 68
4 CoreFoundation 0x00000001bda321e0 __handleUncaughtException + 688
5 libobjc.A.dylib 0x00000001bcc01e4c _objc_terminate() + 108
6 VW-R-CLUB Member APP 0x0000000104555c4c BITCrashUncaughtCXXTerminateHandler() (BITCrashCXXExceptionHandler.mm:183)
7 libc++abi.dylib 0x00000001bcbf50fc std::__terminate(void (*)()) + 12
8 libc++abi.dylib 0x00000001bcbf5188 std::terminate() + 80
9 libdispatch.dylib 0x00000001bd46a498 _dispatch_client_callout + 32
10 libdispatch.dylib 0x00000001bd411bd0 _dispatch_lane_serial_drain$VARIANT$mp + 588
11 libdispatch.dylib 0x00000001bd41274c _dispatch_lane_invoke$VARIANT$mp + 480
12 libdispatch.dylib 0x00000001bd411a9c _dispatch_lane_serial_drain$VARIANT$mp + 280
13 libdispatch.dylib 0x00000001bd412718 _dispatch_lane_invoke$VARIANT$mp + 428
14 libdispatch.dylib 0x00000001bd41aeb8 _dispatch_workloop_worker_thread + 596
15 libsystem_pthread.dylib 0x00000001bd64d0dc _pthread_wqthread + 308
16 libsystem_pthread.dylib 0x00000001bd64fcec start_wqthread + 0
First, the code you show is not the one to be found in github. Do you synchronize all usages of _commandQueue, or only this one? If only this one, why aren't the others synchronized?
Then, in github I find multiple usages of _commandQueue, some of them in methods that are named async..., but also some not async, like cancelPendingCommands or responseCompleted. You need to find out what is the intention of async in a method name, and why methods like cancelPendingCommands is not somehow async.
So the main idea seems to protect all _commandQueue accesses inside the serial _dispatchQueue. This is already the case in the async... methods: They are called from within that queue:
dispatch_async( _dispatchQueue, ^{
[self asyncEnqueueInternalCommand:internalCommand];
});
So you need to ensure that every access to _commandQueue is enqueued in this queue, e.g. change cancelPendingCommands to something like
-(void)cancelPendingCommands
{
dispatch_async( _dispatchQueue, ^{
// This cancels all but the first command in order to prevent sending a new command while
// the response to an active command is still pending. OBD2 adapters usually can't cope with
// that and emit a 'STOPPED' response in that case.
if ( _hasPendingAnswer )
{
NSRange allButTheFirst = NSMakeRange( 1, _commandQueue.count - 1 );
[_commandQueue removeObjectsInRange:allButTheFirst];
}
else
{
[_commandQueue removeAllObjects];
}
});
}
(or create a dedicated asyncCancelPendingCommands function, that will be called from cancelPendingCommands from inside a dispatch block. And so on.
P.S. If you need synchronous execution, you could also use dispatch_sync instead of dispatch_async, but then you have to ensure that you do not create deadlocks.