am 1d0fa397: Merge "fix a race condition in undoDequeue(), where \'tail\'... (9ab5edd2) · Commits · e / os / android_frameworks_base

include/private/surfaceflinger/SharedBufferStack.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -167,6 +167,7 @@ protected:
		SharedBufferStack* const mSharedStack;
		const int mNumBuffers;
		const int mIdentity;
		int32_t computeTail() const;

		friend struct Update;
		friend struct QueueUpdate;
		@@ -260,8 +261,6 @@ private:
		friend struct DequeueCondition;
		friend struct LockCondition;

		int32_t computeTail() const;

		struct QueueUpdate : public UpdateBase {
		inline QueueUpdate(SharedBufferBase* sbb);
		inline ssize_t operator()();
		@@ -288,6 +287,7 @@ private:
		};

		int32_t tail;
		int32_t undoDequeueTail;
		// statistics...
		nsecs_t mDequeueTime[NUM_BUFFER_MAX];
		};

libs/surfaceflinger_client/SharedBufferStack.cpp

+11 −24

Original line number	Diff line number	Diff line
		@@ -179,7 +179,7 @@ String8 SharedBufferBase::dump(char const* prefix) const
		char buffer[SIZE];
		String8 result;
		SharedBufferStack& stack( *mSharedStack );
		int tail = (mNumBuffers + stack.head - stack.available + 1) % mNumBuffers;
		int tail = computeTail();
		snprintf(buffer, SIZE,
		"%s[ head=%2d, available=%2d, queued=%2d, tail=%2d ] "
		"reallocMask=%08x, inUse=%2d, identity=%d, status=%d\n",
		@@ -189,6 +189,12 @@ String8 SharedBufferBase::dump(char const* prefix) const
		return result;
		}

		int32_t SharedBufferBase::computeTail() const
		{
		SharedBufferStack& stack( *mSharedStack );
		return (mNumBuffers + stack.head - stack.available + 1) % mNumBuffers;
		}

		// ============================================================================
		// conditions and updates
		// ============================================================================
		@@ -297,32 +303,12 @@ ssize_t SharedBufferServer::StatusUpdate::operator()() {

		SharedBufferClient::SharedBufferClient(SharedClient* sharedClient,
		int surface, int num, int32_t identity)
		: SharedBufferBase(sharedClient, surface, num, identity), tail(0)
		: SharedBufferBase(sharedClient, surface, num, identity),
		tail(0), undoDequeueTail(0)
		{
		tail = computeTail();
		}

		int32_t SharedBufferClient::computeTail() const
		{
		SharedBufferStack& stack( *mSharedStack );
		// we need to make sure we read available and head coherently,
		// w.r.t RetireUpdate.
		int32_t newTail;
		int32_t avail;
		int32_t head;
		do {
		avail = stack.available;
		head = stack.head;
		} while (stack.available != avail);
		newTail = head - avail + 1;
		if (newTail < 0) {
		newTail += mNumBuffers;
		} else if (newTail >= mNumBuffers) {
		newTail -= mNumBuffers;
		}
		return newTail;
		}

		ssize_t SharedBufferClient::dequeue()
		{
		SharedBufferStack& stack( *mSharedStack );
		@@ -350,6 +336,7 @@ ssize_t SharedBufferClient::dequeue()

		int dequeued = tail;
		tail = ((tail+1 >= mNumBuffers) ? 0 : tail+1);
		undoDequeueTail = dequeued;
		LOGD_IF(DEBUG_ATOMICS, "dequeued=%d, tail=%d, %s",
		dequeued, tail, dump("").string());

		@@ -363,7 +350,7 @@ status_t SharedBufferClient::undoDequeue(int buf)
		UndoDequeueUpdate update(this);
		status_t err = updateCondition( update );
		if (err == NO_ERROR) {
		tail = computeTail();
		tail = undoDequeueTail;
		}
		return err;
		}