Question

I have a thread that modifies a passed pointer to an object (which is alloc’d and retained in the calling thread) in a loop. If I put the pointer in the autorelease pool, I sometimes get errors because the object is being released when it shouldn’t. I took it out of the autorelease pool and this seems to work. However, I am worried about a memory leak because if I don’t use an autorelease pool at all, I get a severe leak.

-(void)my_thread:(NSArray*)parameters;
{       
    //keep this out of the autorelease pool
    Object *theObject;
    [[parameters objectAtIndex:2] getValue:&theObject];

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    //do stuff to theObject

    [pool release];
}

Answer 1

Given this:

-(void)my_thread:(NSArray*)parameters;
{       
...
}

The only way for parameters to be valid when said method is the entry point to a thread is if parameters has been retained by the spawning thread. Not retained and autoreleased, but simply retained.

In other words: autorelease pools can never contribute to thread safety. An autoreleased object can never traverse thread boundaries safely. There must be a hard retain of the object in the sending thread and the receiving thread must release said object. End of story.

Or codewise:

-(void)my_thread:(NSArray*)parameters;
{     
    ... do your stuff here, including your autorelease pool dance
    [parameters release];  
}