LTOBD2Adapter: Race Condition in Command Queue Access

-(void)asyncEnqueueInternalCommand:(LTOBD2AdapterInternalCommand*)internalCommand
{
    **[_commandQueue addObject:internalCommand];**
    [self asyncProcessCommandQueue];
}
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM insertObject:atIndex:]: index 7191 beyond bounds [0 .. 7189]'

Can you help me to figure out what has happend. I record over 30 Minutes rpm and speed and 4 Other values.

Tested this in debug and _commandQueue is between 1 and 6 after adding commands.
i dont know why it can go up to 7000.
And why it is possible to get this Error: index beyond bounds

i will try it with this solution:

if ( [_commandQueue count] > 200 )
{
    NSLog( @"cancelPendingCommands : Has more than 200" );
    [self cancelPendingCommands];
}

after: asyncProcessCommandQueue

Thanks for this report. The actual problem looks like a multithreading race condition – I should check whether access of the command queue is a) coordinated or b) make the command queue thread-safe.

That said, if you're checking values in a loop, you have to take care that you're not adding commands faster than they are handled, so instead of adding based on a timer it would be better to use the completion handler to schedule the next iteration.

Last but not least, there are several optimizations that I want to tackle in 2019, namely adding facilities to group multiple PID queries (in order to save bandwidth), and also something to ease repeating queries.

created an outlet for the queue count and slow down the new requests if needed.
for me its currently ok.
Thank you for detailed answer 👍

Have you any idea how to fix this ?
Yesterday it was 0...4 [index 6 beyond bounds]

I start the "transmitMultipleCommands" function in the main queue but it doesn´t help.

This Error only happens all >50.000 readings so its hard to find the error but i think this might be help.

-(void)asyncEnqueueInternalCommand:(LTOBD2AdapterInternalCommand*)internalCommand
{
    @synchronized(self) {
        [_commandQueue addObject:internalCommand];
        [self asyncProcessCommandQueue];
    }
}

@synchronized

@synchronized(self) is not the solution.
Now i test with the serial dispatchqueue.

created pull request for the solution. #26

Navigation Menu

Repository navigation

LTOBD2Adapter: Race Condition in Command Queue Access #22

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

LTOBD2Adapter: Race Condition in Command Queue Access #22

Description

Activity

Skyb0rg commented on Dec 20, 2018

mickeyl commented on Dec 21, 2018

Skyb0rg commented on Dec 22, 2018

Skyb0rg commented on Jan 3, 2019

Skyb0rg commented on Feb 1, 2019

Skyb0rg commented on Feb 15, 2019

Skyb0rg commented on Mar 15, 2019

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions