Question

I’m getting sporadic EXC_BAD_ACCESS crashes which I’m thinking has to do with multi-threading issues. (I tried profiling with Zombies, but the app doesn’t crash when profiling). So I’m wondering if there is any sort of mechanism, for debugging purposes, to determine if an object is being simultaneously accessed by more than one thread? Maybe somehow print a log statement if that is the case?

Answer 1

A simple and dirty method of telling if you are the only one executing on a thread would rely on unguarded static variables:

-(void)concurrentMethod {
    static NSThread *runningThread = nil;
    NSThread *myThread = [NSThread currentThread];
    if (runningThread != nil) {
        NSLog(@"Thread %@: running concurrently with %@", runningThread, myThread);
    }
    runningThread = myThread;

    ... // Do the useful stuff here

    if (runningThread != myThread) {
        NSLog(@"Thread %@: pre-empted by %@", myThread, runningThread);
    }
    runningThread = nil;
}