[libcamera-devel] [PATCH v3 6/8] android: Guard access to the camera state

[Jacopo Mondi]

Guard access to the camera state and the start/stop sequences
with a mutex.

Currently only stop() and the first call to processCaptureRequest()
start and stop the camera, and they're not meant to race with each
other. With the introduction of flush() the camera can be stopped
concurrently to a processCaptureRequest() call, hence access to the
camera state will need to be protected.

Prepare for that by guarding the existing paths with a mutex.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
---
 src/android/camera_device.cpp | 23 ++++++++++++++---------
 src/android/camera_device.h   |  1 +
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
index fceae96a8b7c..6645c019410e 100644
--- a/src/android/camera_device.cpp
+++ b/src/android/camera_device.cpp
@@ -759,6 +759,7 @@ void CameraDevice::close()
 
 void CameraDevice::stop()
 {
+	MutexLocker cameraLock(cameraMutex_);
 	if (state_ == CameraStopped)
 		return;
 
@@ -1844,17 +1845,21 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
 	if (!isValidRequest(camera3Request))
 		return -EINVAL;
 
-	/* Start the camera if that's the first request we handle. */
-	if (state_ == CameraStopped) {
-		worker_.start();
+	{
+		MutexLocker cameraLock(cameraMutex_);
 
-		int ret = camera_->start();
-		if (ret) {
-			LOG(HAL, Error) << "Failed to start camera";
-			return ret;
-		}
+		/* Start the camera if that's the first request we handle. */
+		if (state_ == CameraStopped) {
+			worker_.start();
 
-		state_ = CameraRunning;
+			int ret = camera_->start();
+			if (ret) {
+				LOG(HAL, Error) << "Failed to start camera";
+				return ret;
+			}
+
+			state_ = CameraRunning;
+		}
 	}
 
 	/*
diff --git a/src/android/camera_device.h b/src/android/camera_device.h
index 995b423c6deb..6fe5454c6535 100644
--- a/src/android/camera_device.h
+++ b/src/android/camera_device.h
@@ -119,6 +119,7 @@ private:
 
 	CameraWorker worker_;
 
+	libcamera::Mutex cameraMutex_; /* Protects access to the camera state. */
 	State state_;
 
 	std::shared_ptr<libcamera::Camera> camera_;
-- 
2.31.1