SCI: avoid deadlocks by using only one mutex #3933
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Make use of the mixer's mutex instead of creating a new one. Otherwise there can still be lock-ups when the main thread and the mixer thread lock each other up in different mutexes (causing a deadlock/freeze). I just noticed this with KQ5 FM-Towns. We had the same issue in AGOS, it was fixed by allowing to access the mixer's mutex. We can use the same thing here...
sluicebox
reviewed
Jun 2, 2022
| @@ -260,7 +260,7 @@ class SciMusic : public Common::Serializable { | |||
| // MIDI parser and to the MIDI driver/player. Note that guarded code must NOT | |||
| // include references to the mixer, otherwise there will probably be situations | |||
| // where a deadlock can occur | |||
| Common::Mutex _mutex; | |||
| Common::Mutex &_mutex; | |||
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Do the comments for _mutex need updating now that it's a reference to the mixer's mutex?
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You're right, I have updated the comment which has become somewhat incorrect. If you have a ref to the mixer's own mutex you can have as many mixer calls as you want inside the guarded space.
(after turning _mutex into a reference to the mixers's mutex)
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Well done finding this deadlock! The change makes sense, as it avoids deadlocks between threads. |
bluegr
approved these changes
Jun 3, 2022
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Make use of the mixer's mutex instead of creating a new one. Otherwise there can still be lock-ups when the main thread and the mixer thread lock each other up in different mutexes (causing a deadlock/freeze). I just noticed this with KQ5 FM-Towns.
We had the same issue in AGOS, it was fixed by allowing access to the mixer's mutex. We can use the same thing here...