[libcamera-devel] [RFC PATCH 2/2] libcamera: PipelineHandler: Retry queuing a capture request

[Hirokazu Honda]

PipelineHandler::queueRequestDevice() fails due to a buffer
shortage. We should retry queuing a capture request later in the
case.

Signed-off-by: Hirokazu Honda <hiroh at chromium.org>
---
 include/libcamera/internal/pipeline_handler.h |  2 +
 src/libcamera/pipeline_handler.cpp            | 57 +++++++++++++++++--
 2 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/include/libcamera/internal/pipeline_handler.h b/include/libcamera/internal/pipeline_handler.h
index 763da63e..e6f771a6 100644
--- a/include/libcamera/internal/pipeline_handler.h
+++ b/include/libcamera/internal/pipeline_handler.h
@@ -44,6 +44,7 @@ public:
 	virtual ~CameraData() = default;
 
 	PipelineHandler *pipe_;
+	std::queue<Request *> waitedRequests_;
 	std::deque<Request *> queuedRequests_;
 	ControlInfoMap controlInfo_;
 	ControlList properties_;
@@ -99,6 +100,7 @@ protected:
 	CameraManager *manager_;
 
 private:
+	void tryQueueRequests(CameraData *data);
 	void mediaDeviceDisconnected(MediaDevice *media);
 	virtual void disconnect();
 
diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
index 4cb58084..18952a1b 100644
--- a/src/libcamera/pipeline_handler.cpp
+++ b/src/libcamera/pipeline_handler.cpp
@@ -70,6 +70,16 @@ LOG_DEFINE_CATEGORY(Pipeline)
  * and remains valid until the instance is destroyed.
  */
 
+/**
+ * \var CameraData::waitedRequests_
+ * \brief The queue of not yet queued request
+ *
+ * The queue of not yet queued request is used to track requests that are not
+ * queued in order to retry queueing them when a pipeline is ready to accept.
+ *
+ * \sa PipelineHandler::queueRequest(), PipelineHandler::tryQueueRequests().
+ */
+
 /**
  * \var CameraData::queuedRequests_
  * \brief The queue of queued and not yet completed request
@@ -378,12 +388,44 @@ void PipelineHandler::queueRequest(Request *request)
 
 	Camera *camera = request->camera_;
 	CameraData *data = cameraData(camera);
-	data->queuedRequests_.push_back(request);
+	data->waitedRequests_.push(request);
+
+	tryQueueRequests(data);
+}
+
+/**
+ * \fn PipelineHandler::tryQueueRequests()
+ * \brief Queue requests that are not yet queued.
+ * \param[in] data The camera data whose waited requests are tried to queue.
+ *
+ * This tries to queue as many requests as possible in order of the
+ * waitedRequests_ in data. If queuing fails due to a buffer shortage, this
+ * method stops and the next call of this method starts from the request that
+ * fails in the previous call. On any other failures, the request is marked as
+ * complete and proceed the successive requests.
+ *
+ * \context This function shall be called from the CameraManager thread.
+ */
+void PipelineHandler::tryQueueRequests(CameraData *data)
+{
+	while (!data->waitedRequests_.empty()) {
+		Request *request = data->waitedRequests_.front();
+		Camera *camera = request->camera_;
+		ASSERT(data == cameraData(camera));
+
+		data->queuedRequests_.push_back(request);
+		int ret = queueRequestDevice(camera, request);
+		if (ret == -ENOBUFS || ret == -ENOMEM) {
+			data->queuedRequests_.pop_back();
+			break;
+		}
 
-	int ret = queueRequestDevice(camera, request);
-	if (ret) {
-		request->result_ = ret;
-		completeRequest(request);
+		data->waitedRequests_.pop();
+		if (ret) {
+			request->result_ = ret;
+			completeRequest(request);
+			break;
+		}
 	}
 }
 
@@ -440,6 +482,9 @@ bool PipelineHandler::completeBuffer(Request *request, FrameBuffer *buffer)
  * submission order, the pipeline handler may call it on any complete request
  * without any ordering constraint.
  *
+ * There might be requests that are waiting to be queued, this triggers
+ * tryQueueRequests().
+ *
  * \context This function shall be called from the CameraManager thread.
  */
 void PipelineHandler::completeRequest(Request *request)
@@ -459,6 +504,8 @@ void PipelineHandler::completeRequest(Request *request)
 		data->queuedRequests_.pop_front();
 		camera->requestComplete(req);
 	}
+
+	tryQueueRequests(data);
 }
 
 /**
-- 
2.31.0.291.g576ba9dcdaf-goog