xCode for iPhone EXC_BAD_ACCESS error only occurs when stepping through the debugger?

Question

I am working on a project in xCode for iPhone where I am receiving an EXC_BAD_ACCESS error, HOWEVER, I only receive the error when stepping through a function I am trying to debug. When I take my breakpoint off the function, but still run the project in Debug Mode, I never receive this error. Is there anyway to solve this or find out what is causing the EXC_BAD_ACCESS error.

The error comes on the line: for ( BEUCharacterAIBehavior *behavior in behavior_.behaviors )

However when stepping through the value behavior_.behaviors is allocated and retained. NSZombiesEnabled is set but still get the cryptic error message.

Code:

-(BEUCharacterAIBehavior *)getHighestValueBehaviorFromBehavior:(BEUCharacterAIBehavior *)behavior_ {
//if the behavior is a leaf then stop checking because there are no sub behaviors
if([behavior_ isLeaf]) return behavior_;


//temp variable for highest value behavior so far
BEUCharacterAIBehavior *highest = nil;
//NSLog(@"BEHAVIORS:%@",behavior_.behaviors);
for ( BEUCharacterAIBehavior *behavior in behavior_.behaviors )
{

    //if there is a highest value behavior check if the highest value behavior has a larger value than the new one
    if(highest)
    {
        if(highest.lastValue > behavior.value) continue;
    }

    //if there is no current behavior then the highest is now the behavior were checking because we have nothing to check against
    if(!currentBehavior) highest = behavior;
    //Make sure the current behavior is not the same behavior as the new one
    else if(currentBehavior != behavior)
    {
        //can the new behaviors parent run multiple times in a row
        if(!behavior.parent.canRunMultipleTimesInARow)
        {
            //make sure the current and new behaviors parents arent the same if they are continue to next behavior
            if(currentBehavior.parent != behavior.parent)
            {
                continue;
            }
        }

        highest = behavior;
        //If current behavior and new behavior are the same make sure they can run multiple times
    } else if(currentBehavior.canRunMultipleTimesInARow)
    {
        highest = currentBehavior;
    }
}
//NSLog(@"GOING TO GET HIGHEST VALUE BEHAVIOR FROM BEHAVIOR: %d",highest.retainCount);
if(!highest) return nil;
return [self getHighestValueBehaviorFromBehavior:highest];//highest;

}

Error stack

0 0x02aebdcb in object_getClass
1 0x00002ac0 in
2 0x00014bb9 in -[BEUCharacterAI getHighestValueBehaviorFromBehavior:] at BEUCharacterAI.m:115
3 0x00014b6b in -[BEUCharacterAI getHighestValueBehavior] at BEUCharacterAI.m:103
4 0x00014904 in -[BEUCharacterAI update:] at BEUCharacterAI.m:68
5 0x00008975 in -[BEUCharacter step:] at BEUCharacter.m:229
6 0x00022aeb in -[EskimoCharacter step:] at EskimoCharacter.m:28
7 0x0000ed2b in -[BEUObjectController step:] at BEUObjectController.m:381
8 0x00003651 in -[BEUGame step:] at BEUGame.m:63
9 0x0007cc42 in -[CCTimer fire:] at CCScheduler.m:87
10 0x0007d846 in -[CCScheduler tick:] at CCScheduler.m:212
11 0x000500b3 in -[CCDirector mainLoop] at CCDirector.m:208
12 0x000532b3 in -[CCDisplayLinkDirector preMainLoop:] at CCDirector.m:1055
13 0x00796f06 in CA::Display::DisplayLink::dispatch
14 0x0079704b in CA::Display::EmulatorDisplayLink::callback
15 0x029810f3 in CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION
16 0x02982734 in __CFRunLoopDoTimer
17 0x028df689 in __CFRunLoopRun
18 0x028dec00 in CFRunLoopRunSpecific
19 0x028deb21 in CFRunLoopRunInMode
20 0x03e96378 in GSEventRunModal
21 0x03e9643d in GSEventRun
22 0x0083bf89 in UIApplicationMain
23 0x00002b50 in main at main.m:13

Answer 1

I was having this with Xcode 4.2.1 and lldb. Switching to gdb solved the problem.

Answer 2

It's not immediately clear to me what your problem is, but this document might help:

Mac OS X Debugging Magic

Answer 3

Do you have other threads running? It could be that something else is modifying behavior_.behaviors or simply behavior_ while your loop is running, but the window is quite small unless the loop is running really slowly. You could try putting a long sleep in the loop to simulate debugging and see if that makes the crash happen when running outside the debugger.

Answer 4

I have seen this as well under XCode 4 running unit tests in the simulator. At this point I'm chalking it up to a bug in the iOS Simulator somewhere.

I'll edit this answer if I discover more.