HAL IO thread priority and glitching
HAL IO thread priority and glitching
- Subject: HAL IO thread priority and glitching
- From: "Stephen F. Booth" <email@hidden>
- Date: Wed, 18 Sep 2013 19:43:21 -0400
I recently encountered a predictable, reproducible glitch while working on some audio code. In a simple Cocoa application any time I would pull down the Help menu for the first time (or occasionally open NSOpenPanel for the first time) I would receive a kAudioDeviceProcessorOverload notification accompanied by an audible glitch. Even though I perform no blocking operations in my IOProc I can't seem to eliminate the issue; in fact, simply returning noErr still resulted in the overload. I was able to reduce this down to a test case using an AUGraph consisting of two AUs, an AudioFilePlayer unit driving a HALOutput unit in a boilerplate Xcode Cocoa non-NSDocument application. I've posted the code on github at https://gist.github.com/sbooth/6617154
After launching the app and opening a file, pulling down the Help menu (the first time only) results in a glitch and kAudioDeviceProcessorOverload notification nearly 100% of the time. I know that the HAL IO thread is a real time, high priority thread so I was surprised to have this happen. Is there a bug somewhere in my code that I can't see? I've tried everything I can think of to remedy the situation to no avail. Since the bug happens in my code as well as Apple's I'm stumped.
I should mention I'm running 10.8.5 on a MacBookPro8,2.
Stephen
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