On Apr 26, 2011, at 2:55 AM, Vera Tkachenko wrote:

> In my app I need to determine if some app if properly codesigned. To do this 
> I just invoke "/usr/bin/codesign" and analyse return value. To invoke it I 
> use NSTask and launch it in background thread. Everything works fine excepts 
> strange crash I get sometimes from our customers. While NSTask is waiting for 
> command to finish (waitUntilExit) UI starts to update in background thread... 
> which causes crashes. I now that's improper to do any UI related stuff in 
> background threads. And I don't force UI update explicitly.
> 
> But why it's get updated while waiting?

-[NSTask waitUntilExit] runs the current thread's run loop in the default mode. 
 Because of this, it is kind of dangerous -- it will service any input sources, 
timers, delayed performSelector... invocations, etc. that are scheduled in the 
default mode.

Now, the normal way to work around this is to run it on a secondary thread 
where you have a degree of control over what is scheduled on the run loop.  
That's what you are doing, apparently.

So, the question is: what is scheduling a timer or delayed performSelector... 
on that thread's run loop?  It is either some of your own code, or you are 
invoking something in Cocoa which does that as a side effect.  Perhaps 
something is invoking one of the -setNeedsDisplay... methods of an NSView, 
which might implicitly schedule -[NSWindow displayIfNeeded] onto the thread's 
run loop.

Regards,
Ken

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