Merge "Fix a race in BufferQueue" (9642dba1) · Commits · e / os / android_frameworks_native

libs/gui/BufferQueue.cpp

+27 −17

Original line number	Diff line number	Diff line
		@@ -268,7 +268,6 @@ status_t BufferQueue::dequeueBuffer(int outBuf, sp<Fence> outFence, bool async
		usage \|= mConsumerUsageBits;

		int found = -1;
		int dequeuedCount = 0;
		bool tryAgain = true;
		while (tryAgain) {
		if (mAbandoned) {
		@@ -299,14 +298,18 @@ status_t BufferQueue::dequeueBuffer(int outBuf, sp<Fence> outFence, bool async

		// look for a free buffer to give to the client
		found = INVALID_BUFFER_SLOT;
		dequeuedCount = 0;
		int dequeuedCount = 0;
		int acquiredCount = 0;
		for (int i = 0; i < maxBufferCount; i++) {
		const int state = mSlots[i].mBufferState;
		if (state == BufferSlot::DEQUEUED) {
		switch (state) {
		case BufferSlot::DEQUEUED:
		dequeuedCount++;
		}

		if (state == BufferSlot::FREE) {
		break;
		case BufferSlot::ACQUIRED:
		acquiredCount++;
		break;
		case BufferSlot::FREE:
		/* We return the oldest of the free buffers to avoid
		* stalling the producer if possible. This is because
		* the consumer may still have pending reads of the
		@@ -316,6 +319,7 @@ status_t BufferQueue::dequeueBuffer(int outBuf, sp<Fence> outFence, bool async
		mSlots[i].mFrameNumber < mSlots[found].mFrameNumber) {
		found = i;
		}
		break;
		}
		}

		@@ -348,7 +352,13 @@ status_t BufferQueue::dequeueBuffer(int outBuf, sp<Fence> outFence, bool async
		// the max buffer count to change.
		tryAgain = found == INVALID_BUFFER_SLOT;
		if (tryAgain) {
		if (mDequeueBufferCannotBlock) {
		// return an error if we're in "cannot block" mode (producer and consumer
		// are controlled by the application) -- however, the consumer is allowed
		// to acquire briefly an extra buffer (which could cause us to have to wait here)
		// and that's okay because we know the wait will be brief (it happens
		// if we dequeue a buffer while the consumer has acquired one but not released
		// the old one yet -- for e.g.: see GLConsumer::updateTexImage()).
		if (mDequeueBufferCannotBlock && (acquiredCount <= mMaxAcquiredBufferCount)) {
		ST_LOGE("dequeueBuffer: would block! returning an error instead.");
		return WOULD_BLOCK;
		}