What is can draw concurrently interface builder?

Question

I have never used Can draw concurrently option mentioned in iterface builder. See image below:

Can someone explain me its use and purpose?

Answer 1

You can use it to inform AppKit that your NSView subclass' -drawRect: instance method may be called from a secondary thread.

It's 10.6+. When/if AppKit renders views asynchronously, -drawRect: is performed using concurrent blocks, and your -drawRect: will be called from a secondary thread. This means your subclass' implementation must be threadsafe (for compatibility, it is disabled by default).

See also -[NSView setCanDrawConcurrently:] for details, because there are few things required to actually enable this behaviour. As well, it shouldn't imply that AppKit is threadsafe or that its NSView subclasses are designed to support this functionality - It's designed for your heavy drawing.