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# Threading and synchronization

There are three kinds of threads relevant to audio processing.

* Audio engine main thread: This can be either a FIFO writer thread(class `AudioEngine::fifoWriter`)or an audio file renderer thread(class `ProjectRenderer`). They calls `AudioEngine::renderNextBuffer()` which renders audio.
* Audio engine worker threads: They runs rendering subtasks which are queued by the audio engine main thread.
* UI, MIDI, and other threads: They may change parameters or drive instruments.

Non-automated changes may result in race conditions if they aren't synchronized with the audio engine properly. To prevent it, `AudioEngine` provides those functions:

* `requestChangeInModel()`/`doneChangeInModel()`: 

`AudioEngine` handles the calls using `runChangesInModel()`