Re: -[NSThread start] blocks ?!?
Re: -[NSThread start] blocks ?!?
- Subject: Re: -[NSThread start] blocks ?!?
- From: Jerry Krinock <email@hidden>
- Date: Sun, 27 Sep 2015 06:50:41 -0700
> On 2015 Sep 26, at 18:03, Quincey Morris <email@hidden> wrote:
>
> I don’t understand what you’re asking.
I mean that if it is possible for -[NSThread start] to block indefinitely, it is not a useable API. I clicked the “Pause” and “Continue” multiple times in Xcode, but each time, in the main thread, the green arrow was stuck at -[NSThread start], _dispatch_semaphore_wait_slow() and semaphore_wait_trap(). It was apparently waiting for a semaphore.
> The scenario I was talking about involved only delays that would eventually be resolved.
OK, I misunderstood.
> All your stack traces have an identical call to _OSSpinLockLockSlow as their second entry. Looks like everything is waiting on a single lock that’s part of the threading machinery.
Interestisng.
> Since you’ve apparently created over 450 threads previously, perhaps you used up kernel resources to the point where whatever took the lock crashed without releasing it?
I should have mentioned that, of those 450 threads, only about 10 were still showing in the Debug Navigator, which I presume means that thother 440 have finished.
* * *
On 2015 Sep 27, at 03:49, Ken Thomases <email@hidden> wrote:
> It could be a bug in the system libraries, but it could also be any number of other things. For example, a heap smashing bug could have corrupted a GCD-internal spin lock variable.
Arghhhh.
> You could also try to reproduce the problem with a very much simplified test app. That would be the first step in filing a bug report, anyway.
Yesterday, this happened once or twice out of 12 trials, while running the last 10.11 developer preview. I’ve now updated to the GM candidate and so far good after 2 trials. We’ll see. I’m not sure I know how to reproduce :(
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