site_archiver@lists.apple.com Delivered-To: cocoa-dev@lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quevivadev.com; s=default; t=1660761158; bh=FGEcHvuDT0+W7RuORBkwzQCxB2itphW3Qcsx47BVQ3U=; h=From:Subject:Date:References:To:In-Reply-To; b=eT1Tq3vMfLPNHUb07dIAhDxLO1aErgbUNipVAbB0ZBcg4FPNhkMpFiqbmADpR690P kuQbKfsvlIPz5wa/iBLqNRJxDcvu+dGF91iQ4lgM6pHVpi9Pi7/frvXYbPM7TuG5bP 4K5I5dzULI1L99I32HVmt0839N6Dko/xc6Tbkfbk= I have an app that does some image processing, and when I tried to use GCD it created several hundred threads which didn’t work very well. NSOperationQueue allows you to set the max concurrent operations, and the batch exporting process fully utilizes all logical cores on the CPU. opsQueue.maxConcurrentOperationCount = NSProcessInfo.processInfo.processorCount; Maybe I was using GCD wrong, or maybe reading, processing, and writing several hundred images is not a good fit for GCD concurrent queue? In any case NSOperationQueue is easy to use and works well. Jim Crate

On Aug 16, 2022, at 3:37 PM, Jack Brindle via Cocoa-dev <cocoa-dev@lists.apple.com> wrote:

Instead of using NSOperationQueue, I would use GCD to handle the tasks. Create a new Concurrent queue (dispatch_queue_create(DISPATCH_QUEUE_CONCURRENT)), then enqueue the individual items to the queue for processing (dispatch_async(), using the queue created above). Everything can be handled in blocks, including the completion routines. As Christian says the problem then is that data may not be in the original order so you will probably want to sort the returned objects when done. This should significantly speed up the time to do the whole task.

Jack

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On Aug 16, 2022, at 12:26 PM, Steve Christensen via Cocoa-dev <cocoa-dev@lists.apple.com> wrote:

You mentioned creating and managing threads on your own, but that’s what NSOperationQueue —and the lower-level DispatchQueue— does. It also will be more efficient with thread management since it has an intimate understanding of the capabilities of the processor, etc., and will work to do the “right thing” on a per-device basis.

By leveraging NSOperationQueue and then keeping each of the queue operations focused on a single file then you’re not complicating the management of what to do next since most of that is handled for you. Let NSManagedObjectQueue do the heavy lifting (scheduling work) and focus on your part of the task (performing the work).

Steve

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On Aug 16, 2022, at 8:41 AM, Gabriel Zachmann <zach@cs.uni-bremen.de> wrote:

That is a good idea. Thanks a lot!

Maybe, I can turn this into more fine-grained, dynamic load balancing (or latency hiding), as follows: create a number of threads (workers); as soon as a worker is finished with their "current" image, it gets the next one (a piece of work) out of the list, processes it, and stores the iso_date in the output array (dates_and_times). Both accesses to the pointer to the currently next piece of work, and the output array would need to be made exclusive, of course.

Best regards, Gabriel

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