Commit e4e0a12901321a1dd6f949fa0a385684c2a17553
2023-06-12T15:26:34
Reduce the chance of destroying the joystick mutex while it's in use Fixes https://github.com/libsdl-org/SDL/issues/7811 (cherry picked from commit 6390165fd4c193631d6780758a4aeec0d02b90eb)
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diff --git a/src/joystick/SDL_joystick.c b/src/joystick/SDL_joystick.c
index c3120e7..02d7edd 100644
--- a/src/joystick/SDL_joystick.c
+++ b/src/joystick/SDL_joystick.c
@@ -114,6 +114,7 @@ static SDL_JoystickDriver *SDL_joystick_drivers[] = {
static
#endif
SDL_mutex *SDL_joystick_lock = NULL; /* This needs to support recursive locks */
+static SDL_atomic_t SDL_joystick_lock_pending;
static int SDL_joysticks_locked;
static SDL_bool SDL_joysticks_initialized;
static SDL_bool SDL_joysticks_quitting = SDL_FALSE;
@@ -143,23 +144,35 @@ SDL_bool SDL_JoysticksQuitting(void)
void SDL_LockJoysticks(void)
{
+ SDL_AtomicIncRef(&SDL_joystick_lock_pending);
SDL_LockMutex(SDL_joystick_lock);
+ SDL_AtomicDecRef(&SDL_joystick_lock_pending);
++SDL_joysticks_locked;
}
void SDL_UnlockJoysticks(void)
{
+ SDL_mutex *joystick_lock = SDL_joystick_lock;
+ SDL_bool last_unlock = SDL_FALSE;
+
--SDL_joysticks_locked;
- SDL_UnlockMutex(SDL_joystick_lock);
+ if (!SDL_joysticks_initialized) {
+ if (!SDL_joysticks_locked && SDL_AtomicGet(&SDL_joystick_lock_pending) == 0) {
+ /* NOTE: There's a small window here where another thread could lock the mutex */
+ SDL_joystick_lock = NULL;
+ last_unlock = SDL_TRUE;
+ }
+ }
+
+ SDL_UnlockMutex(joystick_lock);
/* The last unlock after joysticks are uninitialized will cleanup the mutex,
* allowing applications to lock joysticks while reinitializing the system.
*/
- if (SDL_joystick_lock && !SDL_joysticks_locked && !SDL_joysticks_initialized) {
- SDL_DestroyMutex(SDL_joystick_lock);
- SDL_joystick_lock = NULL;
+ if (last_unlock) {
+ SDL_DestroyMutex(joystick_lock);
}
}