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Re: Main Thread UI and Detached Thread


On Mar 31, 2008, at 2:06 PM, Mike wrote:
I suppose it's possible. The spawned thread does a lot of setup then iterates some arrays of a bunch of objects in the filesystem that it needs to delete. The idea is to update the progress bar one increment with each item being deleted. I'm using a MacBook 2.16 Ghz but I doubt that the main thread is too slow to be able to do the updates.

The issue wouldn't be the main thread being too slow, but the worker thread being too fast, as it were. You'd be surprised how often you can be wrong with this kind of stuff. I've wasted hours thinking "It surely can't be x" and then actually measuring and finding it was x all the time. How big is the bunch of objects your program needs to delete? How long does it take to delete one item?

Also, I set a message text item with the name of each item being deleted in the window as the worker thread runs. I never see it change even for an instant. I find it hard to believe that there can't be any visual update no matter how quickly the worker thread completes.

If you change the UI values with setNeedsDisplay: calls, they only get updated once in every iteration of the main run loop. If there's a lot going on on that run loop, you may see just one value change (the last one) or none at all if you reset the values when you're done. If you're using bindings I'm not sure about the timing, but it's definitely not going to be faster than direct calls.

Have you measured how long it takes for your worker thread to complete its task? If it's less than a second, I'm not sure if you need a progress bar at all. A progress bar combined with changing text doesn't make a lot of sense if that updates faster than your user can read anyway, so you might want to tone down the update speed.

Hank

Hank Heijink (Mailinglists) wrote:
Just checking the obvious here - is it possible that your worker thread completes its work so fast that the main run loop hasn't updated the screen once before it's done? Keep in mind that the main thread has to display your window with the progress bar and the text and (depending on your implementation) that your worker thread may be working (and completing) while that's being done.
On Mar 30, 2008, at 2:55 PM, Mike wrote:
I have all my UI running on my app's main thread. I have a worker thread that I detach with detachNewThreadSelector:toTarget:withObject: (my worker thread).

In my worker thread I do a tight processing loop and one of the things I do in the loop is call two methods in the main thread to update the display (a text message and progress bar) - via performSelectorOnMainThread:withObject:waitUntilDone:modes.

However, when the loop runs in the spawned thread, the display doesn't get updated. If I insert a sleep(1) call into the loop, then the display updates.

Why doesn't the main thread process the changes to the UI unless I call sleep? I thought the whole idea of using a separate thread was so that the main thread could continue to run on its own?

Thanks,

Mike



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References: 
 >Main Thread UI and Detached Thread (From: Mike <email@hidden>)
 >Re: Main Thread UI and Detached Thread (From: "Hank Heijink (Mailinglists)" <email@hidden>)
 >Re: Main Thread UI and Detached Thread (From: Mike <email@hidden>)



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