Do a pointer exchange when replacing the source buffer queue

OpenAL32/Include/alMain.h

@@ -235,6 +235,10 @@ static __inline int ExchangeInt(volatile int *ptr, int newval)
 {
     return __sync_lock_test_and_set(ptr, newval);
 }
+static __inline void *ExchangePtr(void *volatile*ptr, void *newval)
+{
+    return __sync_lock_test_and_set(ptr, newval);
+}
 static __inline ALboolean CompExchangeInt(volatile int *ptr, int oldval, int newval)
 {
     return __sync_bool_compare_and_swap(ptr, oldval, newval);
@@ -258,6 +262,10 @@ static __inline int ExchangeInt(volatile int *ptr, int newval)
     } u = { ptr };
     return InterlockedExchange(u.l, newval);
 }
+static __inline void *ExchangePtr(void *volatile*ptr, void *newval)
+{
+    return InterlockedExchangePtr(ptr, newval);
+}
 static __inline ALboolean CompExchangeInt(volatile int *ptr, int oldval, int newval)
 {
     union {
@@ -286,6 +294,14 @@ static __inline int ExchangeInt(volatile int *ptr, int newval)
     } while(!OSAtomicCompareAndSwap32Barrier(oldval, newval, ptr));
     return oldval;
 }
+static __inline void *ExchangePtr(void *volatile*ptr, void *newval)
+{
+    void *oldval;
+    do {
+        oldval = *ptr;
+    } while(!OSAtomicCompareAndSwapPtrBarrier(oldval, newval, ptr));
+    return oldval;
+}
 static __inline ALboolean CompExchangeInt(volatile int *ptr, int oldval, int newval)
 {
     return OSAtomicCompareAndSwap32Barrier(oldval, newval, ptr);

OpenAL32/alSource.c

@@ -559,22 +559,14 @@ AL_API ALvoid AL_APIENTRY alSourcei(ALuint source,ALenum eParam,ALint lValue)
             case AL_BUFFER:
                 if(Source->state == AL_STOPPED || Source->state == AL_INITIAL)
                 {
+                    ALbufferlistitem *oldlist;
                     ALbuffer *buffer = NULL;
 
                     if(lValue == 0 ||
                        (buffer=LookupBuffer(device->BufferMap, lValue)) != NULL)
                     {
-                        // Remove all elements in the queue
-                        while(Source->queue != NULL)
-                        {
-                            BufferListItem = Source->queue;
-                            Source->queue = BufferListItem->next;
-
-                            if(BufferListItem->buffer)
-                                DecrementRef(&BufferListItem->buffer->ref);
-                            free(BufferListItem);
-                        }
                         Source->BuffersInQueue = 0;
+                        Source->BuffersPlayed = 0;
 
                         // Add the buffer to the queue (as long as it is NOT the NULL buffer)
                         if(buffer != NULL)
@@ -587,8 +579,10 @@ AL_API ALvoid AL_APIENTRY alSourcei(ALuint source,ALenum eParam,ALint lValue)
                             BufferListItem->buffer = buffer;
                             BufferListItem->next = NULL;
                             BufferListItem->prev = NULL;
+                            // Increment reference counter for buffer
+                            IncrementRef(&buffer->ref);
 
-                            Source->queue = BufferListItem;
+                            oldlist = ExchangePtr((void**)&Source->queue, BufferListItem);
                             Source->BuffersInQueue = 1;
 
                             Source->NumChannels = ChannelsFromFmt(buffer->FmtChannels);
@@ -597,18 +591,25 @@ AL_API ALvoid AL_APIENTRY alSourcei(ALuint source,ALenum eParam,ALint lValue)
                                 Source->Update = CalcSourceParams;
                             else
                                 Source->Update = CalcNonAttnSourceParams;
-
-                            // Increment reference counter for buffer
-                            IncrementRef(&buffer->ref);
+                            Source->NeedsUpdate = AL_TRUE;
                         }
                         else
                         {
                             // Source is now in UNDETERMINED mode
                             Source->lSourceType = AL_UNDETERMINED;
+                            oldlist = ExchangePtr((void**)&Source->queue, NULL);
                         }
-                        Source->BuffersPlayed = 0;
 
-                        Source->NeedsUpdate = AL_TRUE;
+                        // Delete all previous elements in the queue
+                        while(oldlist != NULL)
+                        {
+                            BufferListItem = oldlist;
+                            oldlist = BufferListItem->next;
+
+                            if(BufferListItem->buffer)
+                                DecrementRef(&BufferListItem->buffer->ref);
+                            free(BufferListItem);
+                        }
                     }
                     else
                         alSetError(pContext, AL_INVALID_VALUE);