Large performance regression fixed by moving mutex further into the Timeline::GetFrame method - only when generating a new frame (allowing cache to actually work freely). Adding mutex back to FFmpegReader::GetFrame. Removing redundant mutex from ReaderBase.h. Adding mutex to all methods that call shrink_to_fit().

src/FFmpegReader.cpp

@@ -206,8 +206,8 @@ int FFmpegReader::IsHardwareDecodeSupported(int codecid)
 void FFmpegReader::Open() {
 	// Open reader if not already open
 	if (!is_open) {
-		// Prevent calls to GetFrame when Closing
-		const std::lock_guard<std::recursive_mutex> lock(processingMutex);
+		// Prevent async calls to the following code
+		const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
 
 		// Initialize format context
 		pFormatCtx = NULL;
@@ -580,8 +580,8 @@ void FFmpegReader::Open() {
 void FFmpegReader::Close() {
 	// Close all objects, if reader is 'open'
 	if (is_open) {
-		// Prevent calls to GetFrame when Closing
-		const std::lock_guard<std::recursive_mutex> lock(processingMutex);
+		// Prevent async calls to the following code
+		const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
 
 		// Mark as "closed"
 		is_open = false;
@@ -881,13 +881,16 @@ std::shared_ptr<Frame> FFmpegReader::GetFrame(int64_t requested_frame) {
 		// Return the cached frame
 		return frame;
 	} else {
-		// Check the cache a 2nd time (due to a potential previous lock)
+
+	    // Prevent async calls to the remainder of this code
+		const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
+		// Check the cache a 2nd time (due to the potential previous lock)
 		frame = final_cache.GetFrame(requested_frame);
 		if (frame) {
 			// Debug output
 			ZmqLogger::Instance()->AppendDebugMethod("FFmpegReader::GetFrame", "returned cached frame on 2nd look", requested_frame);
 
-			// Return the cached frame
 		} else {
 			// Frame is not in cache
 			// Reset seek count
@@ -2078,6 +2081,9 @@ bool FFmpegReader::IsPartialFrame(int64_t requested_frame) {
 // Check the working queue, and move finished frames to the finished queue
 void FFmpegReader::CheckWorkingFrames(int64_t requested_frame) {
 
+	// Prevent async calls to the following code
+	const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
 	// Get a list of current working queue frames in the cache (in-progress frames)
 	std::vector<std::shared_ptr<openshot::Frame>> working_frames = working_cache.GetFrames();
 	std::vector<std::shared_ptr<openshot::Frame>>::iterator working_itr;

src/FrameMapper.cpp

@@ -84,6 +84,9 @@ void FrameMapper::AddField(Field field)
 
 // Clear both the fields & frames lists
 void FrameMapper::Clear() {
+	// Prevent async calls to the following code
+	const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
     // Clear the fields & frames lists
     fields.clear();
     fields.shrink_to_fit();
@@ -104,6 +107,9 @@ void FrameMapper::Init()
 		// Skip initialization
 		return;
 
+	// Prevent async calls to the following code
+	const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
 	// Clear the fields & frames lists
 	Clear();
 

src/Qt/AudioPlaybackThread.cpp

@@ -152,7 +152,7 @@ namespace openshot
     std::shared_ptr<openshot::Frame> AudioPlaybackThread::getFrame()
     {
 	if (source) return source->getFrame();
-	return std::shared_ptr<openshot::Frame>();
+		return std::shared_ptr<openshot::Frame>();
     }
 
 	// Seek the audio thread

src/ReaderBase.h

@@ -77,7 +77,6 @@ namespace openshot
 	protected:
 		/// Mutex for multiple threads
 		std::recursive_mutex getFrameMutex;
-		std::recursive_mutex processingMutex;
 		openshot::ClipBase* clip; ///< Pointer to the parent clip instance (if any)
 
 	public:

src/Timeline.cpp

@@ -853,9 +853,6 @@ bool Timeline::isEqual(double a, double b)
 // Get an openshot::Frame object for a specific frame number of this reader.
 std::shared_ptr<Frame> Timeline::GetFrame(int64_t requested_frame)
 {
-    // Get lock (to prevent the same frame from being generated by more than 1 thread)
-    const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
-
 	// Adjust out of bounds frame number
 	if (requested_frame < 1)
 		requested_frame = 1;
@@ -874,6 +871,9 @@ std::shared_ptr<Frame> Timeline::GetFrame(int64_t requested_frame)
 	}
 	else
 	{
+		// Prevent async calls to the following code
+		const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
 		// Get a list of clips that intersect with the requested section of timeline
 		// This also opens the readers for intersecting clips, and marks non-intersecting clips as 'needs closing'
 		std::vector<Clip*> nearby_clips;