0001264: Turn CriticalSection into shared mutex

ID	Project	Category	View Status	Date Submitted	Last Update

0001264	OpenMPT	General	public	2019-09-22 18:07	2021-11-02 20:51

Reporter	Saga Musix	Assigned To
Priority	normal	Severity	minor	Reproducibility	N/A
Status	new	Resolution	open

Summary	0001264: Turn CriticalSection into shared mutex
Description	We should consider turning the `CriticalSection` lock used to serialize access to `CSoundFile` from different threads into a shared_mutex. Right now the differences are negligible, but in the future there are several ways we can take advantage of this feature: Scripting API: Script access to `CSoundFile` doesn't have to block audio thread if it's just reading Autosave: Can safely run in another thread without blocking GUI and audio thread, but would still block edits made at the same time, obviously. Read access to `const CSoundFile` would go through `shared_lock`, write access to `CSoundFile` would go through `unique_lock`.
Additional Information	As we currently rely on `CriticalSection` being a recursive mutex, and there is no `shared_recursive_mutex` in C++, we'd need to work around that (e.g. like this).
Tags	No tags attached.

Has the bug occurred in previous versions?
Tested code revision (in case you know it)

manx 2020-05-24 12:48 administrator ~0004343	It probably makes sense to split out a separate mutex for the PlayState at the same time. The PlayState is written-to by the audio thread, while the rest of CSoundFile is not.

Saga Musix 2020-05-24 12:53 administrator ~0004344	I thought the same initially but it isn't 100% true: The "invert loop" MOD command modifies sample data, so if we do that, an extra lock would have to be acquired when that command is encountered. The Paula resampler and OPL emulator states (which are not part of PlayState) are also written to in the mixer but there are no heap allocations in those apart from the initial mixer initialization.

Date Modified	Username	Field
2019-09-22 18:07	Saga Musix	New Issue
2020-05-24 12:48	manx	Note Added: 0004343
2020-05-24 12:53	Saga Musix	Note Added: 0004344
2021-11-02 20:51	Saga Musix	Additional Information Updated