android: Guard access to the camera state

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@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/android/camera_device.cpp

@@ -800,6 +800,7 @@ void CameraDevice::close()
 
 void CameraDevice::stop()
 {
+	MutexLocker stateLock(stateMutex_);
 	if (state_ == State::Stopped)
 		return;
 
@@ -1900,6 +1901,9 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
 	if (!isValidRequest(camera3Request))
 		return -EINVAL;
 
+	{
+		MutexLocker stateLock(stateMutex_);
+
 		/* Start the camera if that's the first request we handle. */
 		if (state_ == State::Stopped) {
 			worker_.start();
@@ -1912,6 +1916,7 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
 
 			state_ = State::Running;
 		}
+	}
 
 	/*
 	 * Save the request descriptors for use at completion time.

src/android/camera_device.h

@@ -120,6 +120,7 @@ private:
 
 	CameraWorker worker_;
 
+	libcamera::Mutex stateMutex_; /* Protects access to the camera state. */
 	State state_;
 
 	std::shared_ptr<libcamera::Camera> camera_;