[libcamera-devel] [PATCH 09/13] gstreamer: Use dedicated lock for request queues

[Laurent Pinchart]

Add a new lock to the GstLibcameraSrcState class to protect the queued
and completed requests queues. This replaces the GstObject lock, and
minimizes the lock contention between the request completion handler and
the task run handler as the former must run as fast as possible.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/gstreamer/gstlibcamerasrc.cpp | 39 ++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index e30d45fa2223..b85ba39fb808 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -32,6 +32,8 @@
 #include <queue>
 #include <vector>
 
+#include <libcamera/base/mutex.h>
+
 #include <libcamera/camera.h>
 #include <libcamera/camera_manager.h>
 #include <libcamera/control_ids.h>
@@ -111,8 +113,13 @@ struct GstLibcameraSrcState {
 	std::shared_ptr<Camera> cam_;
 	std::unique_ptr<CameraConfiguration> config_;
 	std::vector<GstPad *> srcpads_;
-	std::queue<std::unique_ptr<RequestWrap>> queuedRequests_;
-	std::queue<std::unique_ptr<RequestWrap>> completedRequests_;
+
+	Mutex lock_;
+	std::queue<std::unique_ptr<RequestWrap>> queuedRequests_
+		LIBCAMERA_TSA_GUARDED_BY(lock_);
+	std::queue<std::unique_ptr<RequestWrap>> completedRequests_
+		LIBCAMERA_TSA_GUARDED_BY(lock_);
+
 	guint group_id_;
 
 	void requestCompleted(Request *request);
@@ -155,12 +162,15 @@ GstStaticPadTemplate request_src_template = {
 void
 GstLibcameraSrcState::requestCompleted(Request *request)
 {
-	GLibLocker lock(GST_OBJECT(src_));
-
 	GST_DEBUG_OBJECT(src_, "buffers are ready");
 
-	std::unique_ptr<RequestWrap> wrap = std::move(queuedRequests_.front());
-	queuedRequests_.pop();
+	std::unique_ptr<RequestWrap> wrap;
+
+	{
+		MutexLocker locker(lock_);
+		wrap = std::move(queuedRequests_.front());
+		queuedRequests_.pop();
+	}
 
 	g_return_if_fail(wrap->request_.get() == request);
 
@@ -183,7 +193,10 @@ GstLibcameraSrcState::requestCompleted(Request *request)
 		wrap->latency_ = sys_now - timestamp;
 	}
 
-	completedRequests_.push(std::move(wrap));
+	{
+		MutexLocker locker(lock_);
+		completedRequests_.push(std::move(wrap));
+	}
 
 	gst_task_resume(src_->task);
 }
@@ -289,16 +302,17 @@ gst_libcamera_src_task_run(gpointer user_data)
 	}
 
 	if (wrap) {
-		GLibLocker lock(GST_OBJECT(self));
 		GST_TRACE_OBJECT(self, "Requesting buffers");
 		state->cam_->queueRequest(wrap->request_.get());
+
+		MutexLocker locker(state->lock_);
 		state->queuedRequests_.push(std::move(wrap));
 
 		/* The RequestWrap will be deleted in the completion handler. */
 	}
 
 	{
-		GLibLocker lock(GST_OBJECT(self));
+		MutexLocker locker(state->lock_);
 
 		if (!state->completedRequests_.empty()) {
 			wrap = std::move(state->completedRequests_.front());
@@ -358,7 +372,7 @@ gst_libcamera_src_task_run(gpointer user_data)
 		bool do_pause;
 
 		{
-			GLibLocker lock(GST_OBJECT(self));
+			MutexLocker locker(state->lock_);
 			do_pause = state->completedRequests_.empty();
 		}
 
@@ -513,7 +527,10 @@ gst_libcamera_src_task_leave([[maybe_unused]] GstTask *task,
 
 	state->cam_->stop();
 
-	state->completedRequests_ = {};
+	{
+		MutexLocker locker(state->lock_);
+		state->completedRequests_ = {};
+	}
 
 	for (GstPad *srcpad : state->srcpads_)
 		gst_libcamera_pad_set_pool(srcpad, nullptr);
-- 
Regards,

Laurent Pinchart