On Jan 5, 2014, at 4:37 PM, Jim O'Connor <[email protected]> wrote:
> 
> When my read stream finishes I schedule a timer to clean up on the runloop to 
> serialize access to shared resources.
> However, I had a hang late last night because a mutex grabbed in the read 
> stream callback handler was held and was also being grabbed when the timer it 
> scheduled to clean up fired INSIDE the callback.
> It was late and I didn't save the odd message in the Xcode stack crawl about 
> the timer being called OUTSIDE of the runloop. And now I can't get it to 
> repeat.
> 
> I was under the impression that timers only fired when the RunLoop was 
> actually the top of the execution stack, or was called explicitly by me. Is 
> this not right?

Well, barring a memory smasher, CFReadStream isn’t going to directly invoke 
your timer callback function.

But your use of “top of the execution stack” seems a little off to me. It’s 
possible to manually run a runloop from a deeper stack frame; this is often 
done by APIs which present a callback interface but need to use asynchrony 
internally.

The run loop doesn’t care that it’s being run from code that itself is being 
indirectly called as a result of a turn of the same run loop, so it will fire 
its timers just like normal. 

--Kyle Sluder
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