Use an internal event to more timely release old effect states

Alc/ALu.c

@@ -462,12 +462,40 @@ static bool CalcEffectSlotParams(ALeffectslot *slot, ALCcontext *context, bool f
             slot->Params.AirAbsorptionGainHF = 1.0f;
         }
 
-        /* Swap effect states. No need to play with the ref counts since they
-         * keep the same number of refs.
-         */
         state = props->State;
-        props->State = slot->Params.EffectState;
-        slot->Params.EffectState = state;
+
+        if(state == slot->Params.EffectState)
+        {
+            /* If the effect state is the same as current, we can decrement its
+             * count safely to remove it from the update object (it can't reach
+             * 0 refs since the current params also hold a reference).
+             */
+            DecrementRef(&state->Ref);
+            props->State = NULL;
+        }
+        else
+        {
+            /* Otherwise, replace it and send off the old one with a release
+             * event.
+             */
+            AsyncEvent evt = ASYNC_EVENT(EventType_ReleaseEffectState);
+            evt.u.EffectState = slot->Params.EffectState;
+
+            slot->Params.EffectState = state;
+            props->State = NULL;
+
+            if(LIKELY(ll_ringbuffer_write(context->AsyncEvents, (const char*)&evt, 1) != 0))
+                alsem_post(&context->EventSem);
+            else
+            {
+                /* If writing the event failed, the queue was probably full.
+                 * Store the old state in the property object where it can
+                 * eventually be cleaned up sometime later (not ideal, but
+                 * better than blocking or leaking).
+                 */
+                props->State = evt.u.EffectState;
+            }
+        }
 
         ATOMIC_REPLACE_HEAD(struct ALeffectslotProps*, &context->FreeEffectslotProps, props);
     }

OpenAL32/Include/alMain.h

@@ -760,6 +760,9 @@ enum {
     EventType_Performance       = 1<<3,
     EventType_Deprecated        = 1<<4,
     EventType_Disconnected      = 1<<5,
+
+    /* Internal events. */
+    EventType_ReleaseEffectState = 65536,
 };
 
 typedef struct AsyncEvent {
@@ -772,6 +775,7 @@ typedef struct AsyncEvent {
             ALuint param;
             ALchar msg[1008];
         } user;
+        struct ALeffectState *EffectState;
     } u;
 } AsyncEvent;
 #define ASYNC_EVENT(t) { t, { 0 } }

OpenAL32/alAuxEffectSlot.c

@@ -753,6 +753,9 @@ void UpdateEffectSlotProps(ALeffectslot *slot, ALCcontext *context)
         /* If there was an unused update container, put it back in the
          * freelist.
          */
+        if(props->State)
+            ALeffectState_DecRef(props->State);
+        props->State = NULL;
         ATOMIC_REPLACE_HEAD(struct ALeffectslotProps*, &context->FreeEffectslotProps, props);
     }
 

OpenAL32/event.c

@@ -6,6 +6,7 @@
 #include "AL/alext.h"
 #include "alMain.h"
 #include "alError.h"
+#include "alAuxEffectSlot.h"
 #include "ringbuffer.h"
 
 
@@ -30,6 +31,12 @@ int EventThread(void *arg)
             quitnow = evt.EnumType == EventType_KillThread;
             if(quitnow) break;
 
+            if(evt.EnumType == EventType_ReleaseEffectState)
+            {
+                ALeffectState_DecRef(evt.u.EffectState);
+                continue;
+            }
+
             enabledevts = ATOMIC_LOAD(&context->EnabledEvts, almemory_order_acquire);
             if(context->EventCb && (enabledevts&evt.EnumType) == evt.EnumType)
                 context->EventCb(evt.u.user.type, evt.u.user.id, evt.u.user.param,