Bug 839628 - Add MIN_UNDEQUEUED_BUFFERS check in GonkNativeWindow::dequeueBuffer(). r=kchen, r=mikeh, a=approval-mozilla-b2g18+

dom/camera/GonkNativeWindow.cpp

@@ -263,6 +263,7 @@ int GonkNativeWindow::dequeueBuffer(android_native_buffer_t** buffer)
 
         int found = -1;
         int dequeuedCount = 0;
+        int renderingCount = 0;
         bool tryAgain = true;
 
         CNW_LOGD("dequeueBuffer: E");
@@ -274,11 +275,15 @@ int GonkNativeWindow::dequeueBuffer(android_native_buffer_t** buffer)
             // look for a free buffer to give to the client
             found = INVALID_BUFFER_SLOT;
             dequeuedCount = 0;
+            renderingCount = 0;
             for (int i = 0; i < mBufferCount; i++) {
                 const int state = mSlots[i].mBufferState;
                 if (state == BufferSlot::DEQUEUED) {
                     dequeuedCount++;
                 }
+                else if (state == BufferSlot::RENDERING) {
+                    renderingCount++;
+                }
                 else if (state == BufferSlot::FREE) {
                     /* We return the oldest of the free buffers to avoid
                      * stalling the producer if possible.  This is because
@@ -292,6 +297,22 @@ int GonkNativeWindow::dequeueBuffer(android_native_buffer_t** buffer)
                 }
             }
 
+            // See whether a buffer has been in RENDERING state since the last
+            // setBufferCount so we know whether to perform the
+            // MIN_UNDEQUEUED_BUFFERS check below.
+            if (renderingCount > 0) {
+                // make sure the client is not trying to dequeue more buffers
+                // than allowed.
+                const int avail = mBufferCount - (dequeuedCount + 1);
+                if (avail < MIN_UNDEQUEUED_BUFFERS) {
+                    CNW_LOGE("dequeueBuffer: MIN_UNDEQUEUED_BUFFERS=%d exceeded "
+                            "(dequeued=%d)",
+                            MIN_UNDEQUEUED_BUFFERS,
+                            dequeuedCount);
+                    return -EBUSY;
+                }
+            }
+
             // we're in synchronous mode and didn't find a buffer, we need to
             // wait for some buffers to be consumed
             tryAgain = (found == INVALID_BUFFER_SLOT);