Add ma_fence object in preparation for changes to async notifications.

research/miniaudio_engine.h

@@ -1127,6 +1127,34 @@ MA_API ma_result ma_slot_allocator_alloc(ma_slot_allocator* pAllocator, ma_uint6
 MA_API ma_result ma_slot_allocator_free(ma_slot_allocator* pAllocator, ma_uint64 slot);
 
 
+
+/*
+Fence
+=====
+This locks while the counter is larger than 0. Counter can be incremented and decremented by any
+thread, but care needs to be taken when waiting. It is possible for one thread to acquire the
+fence just as another thread returns from ma_fence_wait().
+
+The idea behind a fence is to allow you to wait for a group of operations to complete. When an
+operation starts, the counter is incremented which locks the fence. When the operation completes,
+the fence will be released which decrements the counter. ma_fence_wait() will block until the
+counter hits zero.
+*/
+typedef struct
+{
+    ma_event e;
+    ma_uint32 counter;
+} ma_fence;
+
+MA_API ma_result ma_fence_init(ma_fence* pFence);
+MA_API void ma_fence_uninit(ma_fence* pFence);
+MA_API ma_result ma_fence_acquire(ma_fence* pFence);    /* Increment counter. */
+MA_API ma_result ma_fence_release(ma_fence* pFence);    /* Decrement counter. */
+MA_API ma_result ma_fence_wait(ma_fence* pFence);       /* Wait for counter to reach 0. */
+
+
+
+
 /* Notification codes for ma_async_notification. Used to allow some granularity for notification callbacks. */
 #define MA_NOTIFICATION_COMPLETE    0   /* Operation has fully completed. */
 #define MA_NOTIFICATION_FAILED      1   /* Failed to initialize. */
@@ -5753,6 +5781,129 @@ MA_API ma_result ma_slot_allocator_free(ma_slot_allocator* pAllocator, ma_uint64
 
 
 
+#define MA_FENCE_COUNTER_MAX    0x7FFFFFFF
+
+MA_API ma_result ma_fence_init(ma_fence* pFence)
+{
+    ma_result result;
+
+    if (pFence == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    MA_ZERO_OBJECT(pFence);
+    pFence->counter = 0;
+
+    result = ma_event_init(&pFence->e);
+    if (result != MA_SUCCESS) {
+        return result;
+    }
+
+    return MA_SUCCESS;
+}
+
+MA_API void ma_fence_uninit(ma_fence* pFence)
+{
+    if (pFence == NULL) {
+        return;
+    }
+
+    ma_event_uninit(&pFence->e);
+
+    MA_ZERO_OBJECT(pFence);
+}
+
+MA_API ma_result ma_fence_acquire(ma_fence* pFence)
+{
+    if (pFence == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    for (;;) {
+        ma_uint32 oldCounter = c89atomic_load_32(&pFence->counter);
+        ma_uint32 newCounter = oldCounter + 1;
+
+        /* Make sure we're not about to exceed our maximum value. */
+        if (newCounter > MA_FENCE_COUNTER_MAX) {
+            return MA_OUT_OF_RANGE;
+        }
+
+        if (c89atomic_compare_exchange_weak_32(&pFence->counter, &oldCounter, newCounter)) {
+            return MA_SUCCESS;
+        } else {
+            if (oldCounter == MA_FENCE_COUNTER_MAX) {
+                return MA_OUT_OF_RANGE; /* The other thread took the last available slot. Abort. */
+            }
+        }
+    }
+
+    /* Should never get here. */
+    /*return MA_SUCCESS;*/
+}
+
+MA_API ma_result ma_fence_release(ma_fence* pFence)
+{
+    if (pFence == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    for (;;) {
+        ma_uint32 oldCounter = c89atomic_load_32(&pFence->counter);
+        ma_uint32 newCounter = oldCounter - 1;
+
+        if (oldCounter == 0) {
+            return MA_INVALID_OPERATION;    /* Acquire/release mismatch. */
+        }
+
+        if (c89atomic_compare_exchange_weak_32(&pFence->counter, &oldCounter, newCounter)) {
+            if (newCounter == 0) {
+                ma_event_signal(&pFence->e);    /* <-- ma_fence_wait() will be waiting on this. */
+            }
+
+            return MA_SUCCESS;
+        } else {
+            if (oldCounter == 0) {
+                return MA_INVALID_OPERATION;    /* Another thread has taken the 0 slot. Acquire/release mismatch. */
+            }
+        }
+    }
+
+    /* Should never get here. */
+    /*return MA_SUCCESS;*/
+}
+
+MA_API ma_result ma_fence_wait(ma_fence* pFence)
+{
+    if (pFence == NULL) {
+        return MA_INVALID_ARGS;
+    }
+
+    for (;;) {
+        ma_result result;
+        ma_uint32 counter;
+
+        counter = c89atomic_load_32(&pFence->counter);
+        if (counter == 0) {
+            /*
+            Counter has hit zero. By the time we get here some other thread may have acquired the
+            fence again, but that is where the caller needs to take care with how they se the fence.
+            */
+            return MA_SUCCESS;
+        }
+
+        /* Getting here means the counter is > 0. We'll need to wait for something to happen. */
+        result = ma_event_wait(&pFence->e);
+        if (result != MA_SUCCESS) {
+            return result;
+        }
+    }
+
+    /* Should never get here. */
+    /*return MA_INVALID_OPERATION;*/
+}
+
+
+
 MA_API ma_result ma_async_notification_signal(ma_async_notification* pNotification, int code)
 {
     ma_async_notification_callbacks* pNotificationCallbacks = (ma_async_notification_callbacks*)pNotification;