Question

I’m seeing something fairly strange here, I’ve got breakpoints set in various dealloc methods in my app, and on inspection, the retain counts of the object self varies from 1 to 0. When dealloc is called, will the retain count of the object be set to 0 already?

I’m using print (int) [self retainCount] in the console to test this.

The 0’s seem to only appear in the dealloc of my NSOperation‘s that are being run in an NSOperationQueue.

Any idea why this is?

Answer 1

The retain count of your object doesn’t matter in -dealloc. For practical purposes, it’s undefined.

The normal implementation of reference counting uses an external reference count for values greater than zero – see NSIncrementExtraRefCount() and NSDecrementExtraRefCountWasZero(). When the extraRefCount count is zero, the refCount is one. When NSDecrementExtraRefCountWasZero() is called and the extraRefCount is already zero, it returns YES and -dealloc is called. Except when dealing with the return value of NSDecrementExtraRefCountWasZero() there is no way to distinguish a refCount of one from a refCount of zero.

That NSOperation gets a zero refCount suggests it’s not using the normal mechanism.