Question

I’m making a non-garbage-collected MacFUSE Cocoa application, inside of which I want to use a GCD block as a delegate. However, my program crashes during the invocation of the block, leaving only an EXC_BAD_ACCESS in its trail.

My program uses a framework built agains the Mac OS 10.5 SDK that does not support garbage collection (nor 64 bits) and the MacFUSE framework. The program builds with no warning or error as a 32-bit program. Other build settings (such as optimization level) were left to their original values.

So I have my application controller, from which I create this block and call runWithContinuation:

AFSPasswordPrompt* prompt = [[AFSPasswordPrompt alloc] initWithIcon:icon];
dispatch_block_t continuation = ^{
    archive.password = prompt.password;
    [self mountFilesystem:fsController];
    [prompt performSelectorOnMainThread:@selector(release) withObject:nil waitUntilDone:NO];
};
[prompt runWithContinuation:continuation];

runWithContinuation: retains the block and instantiates a nib. The block is called only once the user dismisses the password prompt by pressing the “Open” button.

-(void)runWithContinuation:(dispatch_block_t)block
{
    continuation = [block retain];
    [passwordPrompt instantiateNibWithOwner:self topLevelObjects:NULL];
    imageView.image = image;
    [window makeKeyWindow];
}

-(IBAction)open:(id)sender
{
    continuation();
    [self close];
}

-(void)close
{
    [window close];
    [continuation release];
}

My problem is that when I hit continuation(), my program triggers an EXC_BAD_ACCESS, and the last stack frame is called ??. Right under it is the open: method call.

I really don’t know where it’s coming from. NSZombies are enabled, and they don’t report anything.

Any ideas?

Answer 1

try copying the block instead of retaining it. A block lives on the stack until you call copy, then it is copied to the heap.