Re: UI refresh in background thread while [NSTask waitUntilExit]
Re: UI refresh in background thread while [NSTask waitUntilExit]
- Subject: Re: UI refresh in background thread while [NSTask waitUntilExit]
- From: Ken Thomases <email@hidden>
- Date: Wed, 27 Apr 2011 00:40:45 -0500
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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