[libcamera-devel] [PATCH v2 8/8] android: Implement flush() camera operation

[Jacopo Mondi]

Implement the flush() camera operation in the CameraDevice class
and make it available to the camera framework by implementing the
operation wrapper in camera_ops.cpp.

The flush() implementation stops the Camera and the worker thread and
waits for all in-flight requests to be returned. Stopping the Camera
forces all Requests already queued to be returned immediately in error
state. As flush() has to wait until all of them have been returned, make it
wait on a newly introduced condition variable which is notified by the
request completion handler when the queue of pending requests has been
exhausted.

As flush() can race with processCaptureRequest() protect the requests
queueing by introducing a new CameraState::CameraFlushing state that
processCaptureRequest() inspects before queuing the Request to the
Camera. If flush() has been called while processCaptureRequest() was
executing, return the current Request immediately in error state.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 src/android/camera_device.cpp | 91 +++++++++++++++++++++++++++++++++--
 src/android/camera_device.h   |  9 +++-
 src/android/camera_ops.cpp    |  8 ++-
 3 files changed, 102 insertions(+), 6 deletions(-)

diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
index 7f8c9bd7832d..6d6730a50ec7 100644
--- a/src/android/camera_device.cpp
+++ b/src/android/camera_device.cpp
@@ -750,16 +750,64 @@ int CameraDevice::open(const hw_module_t *hardwareModule)
 
 void CameraDevice::close()
 {
-	streams_.clear();
+	MutexLocker cameraLock(cameraMutex_);
+	if (state_ == CameraFlushing) {
+		MutexLocker flushLock(flushMutex_);
+		flushed_.wait(flushLock, [&] { return state_ != CameraStopped; });
+		camera_->release();
 
+		return;
+	}
+
+	streams_.clear();
 	stop();
 
 	camera_->release();
 }
 
+/*
+ * Flush is similar to stop() but sets the camera state to 'flushing' and wait
+ * until all the in-flight requests have been returned before setting the
+ * camera state to stopped.
+ *
+ * Once flushing is done it unlocks concurrent camera close() calls or new
+ * camera configurations.
+ */
+void CameraDevice::flush()
+{
+	{
+		MutexLocker cameraLock(cameraMutex_);
+
+		if (state_ != CameraRunning)
+			return;
+
+		worker_.stop();
+		camera_->stop();
+		state_ = CameraFlushing;
+	}
+
+	/*
+	 * Now wait for all the in-flight requests to be completed before
+	 * continuing. Stopping the Camera guarantees that all in-flight
+	 * requests are completed in error state.
+	 */
+	{
+		MutexLocker requestsLock(requestsMutex_);
+		flushing_.wait(requestsLock, [&] { return descriptors_.empty(); });
+	}
+
+	/*
+	 * Unlock close() or configureStreams() that might be waiting for
+	 * flush to be completed.
+	 */
+	MutexLocker flushLocker(flushMutex_);
+	state_ = CameraStopped;
+	flushed_.notify_one();
+}
+
+/* Calls to stop() must be protected by cameraMutex_ being held by the caller. */
 void CameraDevice::stop()
 {
-	MutexLocker cameraLock(cameraMutex_);
 	if (state_ == CameraStopped)
 		return;
 
@@ -1652,8 +1700,20 @@ PixelFormat CameraDevice::toPixelFormat(int format) const
  */
 int CameraDevice::configureStreams(camera3_stream_configuration_t *stream_list)
 {
-	/* Before any configuration attempt, stop the camera. */
-	stop();
+	{
+		/*
+		 * If a flush is in progress, wait for it to complete and to
+		 * stop the camera, otherwise before any new configuration
+		 * attempt we have to stop the camera explictely.
+		 */
+		MutexLocker cameraLock(cameraMutex_);
+		if (state_ == CameraFlushing) {
+			MutexLocker flushLock(flushMutex_);
+			flushed_.wait(flushLock, [&] { return state_ != CameraStopped; });
+		} else {
+			stop();
+		}
+	}
 
 	if (stream_list->num_streams == 0) {
 		LOG(HAL, Error) << "No streams in configuration";
@@ -2021,6 +2081,25 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
 	if (ret)
 		return ret;
 
+	/*
+	 * Just before queuing the request, make sure flush() has not
+	 * been called after this function has been executed. In that
+	 * case, immediately return the request with errors.
+	 */
+	MutexLocker cameraLock(cameraMutex_);
+	if (state_ == CameraFlushing || state_ == CameraStopped) {
+		for (camera3_stream_buffer_t &buffer : descriptor.buffers_) {
+			buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
+			buffer.release_fence = buffer.acquire_fence;
+		}
+
+		notifyError(descriptor.frameNumber_,
+			    descriptor.buffers_[0].stream,
+			    CAMERA3_MSG_ERROR_REQUEST);
+
+		return 0;
+	}
+
 	worker_.queueRequest(descriptor.request_.get());
 
 	{
@@ -2050,6 +2129,10 @@ void CameraDevice::requestComplete(Request *request)
 			return;
 		}
 
+		/* Release flush if all the pending requests have been completed. */
+		if (descriptors_.empty())
+			flushing_.notify_one();
+
 		node = descriptors_.extract(it);
 	}
 	Camera3RequestDescriptor &descriptor = node.mapped();
diff --git a/src/android/camera_device.h b/src/android/camera_device.h
index ed992ae56d5d..9c55cc2674b7 100644
--- a/src/android/camera_device.h
+++ b/src/android/camera_device.h
@@ -7,6 +7,7 @@
 #ifndef __ANDROID_CAMERA_DEVICE_H__
 #define __ANDROID_CAMERA_DEVICE_H__
 
+#include <condition_variable>
 #include <map>
 #include <memory>
 #include <mutex>
@@ -42,6 +43,7 @@ public:
 
 	int open(const hw_module_t *hardwareModule);
 	void close();
+	void flush();
 
 	unsigned int id() const { return id_; }
 	camera3_device_t *camera3Device() { return &camera3Device_; }
@@ -92,6 +94,7 @@ private:
 	enum State {
 		CameraStopped,
 		CameraRunning,
+		CameraFlushing,
 	};
 
 	void stop();
@@ -124,6 +127,9 @@ private:
 	libcamera::Mutex cameraMutex_; /* Protects access to the camera state. */
 	State state_;
 
+	libcamera::Mutex flushMutex_; /* Protects the flushed_ condition variable. */
+	std::condition_variable flushed_;
+
 	std::shared_ptr<libcamera::Camera> camera_;
 	std::unique_ptr<libcamera::CameraConfiguration> config_;
 
@@ -135,8 +141,9 @@ private:
 	std::map<int, libcamera::PixelFormat> formatsMap_;
 	std::vector<CameraStream> streams_;
 
-	libcamera::Mutex requestsMutex_; /* Protects descriptors_. */
+	libcamera::Mutex requestsMutex_; /* Protects descriptors_ and flushing_. */
 	std::map<uint64_t, Camera3RequestDescriptor> descriptors_;
+	std::condition_variable flushing_;
 
 	std::string maker_;
 	std::string model_;
diff --git a/src/android/camera_ops.cpp b/src/android/camera_ops.cpp
index 696e80436821..8a3cfa175ff5 100644
--- a/src/android/camera_ops.cpp
+++ b/src/android/camera_ops.cpp
@@ -66,8 +66,14 @@ static void hal_dev_dump([[maybe_unused]] const struct camera3_device *dev,
 {
 }
 
-static int hal_dev_flush([[maybe_unused]] const struct camera3_device *dev)
+static int hal_dev_flush(const struct camera3_device *dev)
 {
+	if (!dev)
+		return -EINVAL;
+
+	CameraDevice *camera = reinterpret_cast<CameraDevice *>(dev->priv);
+	camera->flush();
+
 	return 0;
 }
 
-- 
2.31.1