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Real-time audio programming 101: time waits for nothing (2011)

“The audio processing thread is stalling because the client’s implementation of some XAudio2 callback is doing things that can block the thread, such as accessing the disk, synchronizing with other threads, or calling other functions that may block. Such tasks should be performed by a lower-priority background thread that the callback can signal.” — Microsoft XAudio2 documentation “Your IOProc is making blocking calls to the HAL and it is calling NSLog which allocates memory and blocks in fun and unexpected ways.

For the purposes of this post I consider buffer sizes somewhere in the 1-5ms range to be normal and achievable today on most computers running Windows with WDM, WASAPI or ASIO drivers, with Mac OS X’s native CoreAudio system and with ALSA or JACK on Linux. Some low-level audio libraries such as JACK or CoreAudio use these techniques internally, but you need to be sure you know what you’re doing, that you understand your thread priorities and the exact scheduler behavior on each target operating system (and OS kernel version). Side note: trylocks One related option that may be open to you is to use a non-blocking “try-lock” function that simply returns a failure code instead of blocking if the lock can’t be acquired (pthread_mutex_trylock() on POSIX, TryEnterCriticalSection() on Windows).

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