[libcamera-devel] [PATCH v2 2/2] libcamera: pipeline_handler: Make lock() and unlock() thread-safe

[Jacopo Mondi]

Hi Laurent,

On Mon, Dec 27, 2021 at 01:12:55AM +0200, Laurent Pinchart wrote:
> The PipelineHandler lock() and unlock() functions are documented as
> thread-safe, but they're not. Fix them using a mutex.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
> Changes since v1:
>
> - Add thread safety annotation
> - Comment that lockOwner_ does not indicate ownership of lock_
> ---
>  include/libcamera/internal/pipeline_handler.h | 4 +++-
>  src/libcamera/pipeline_handler.cpp            | 5 +++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/include/libcamera/internal/pipeline_handler.h b/include/libcamera/internal/pipeline_handler.h
> index a7331cedfb16..e5b8ffb4db3d 100644
> --- a/include/libcamera/internal/pipeline_handler.h
> +++ b/include/libcamera/internal/pipeline_handler.h
> @@ -14,6 +14,7 @@
>  #include <sys/types.h>
>  #include <vector>
>
> +#include <libcamera/base/mutex.h>
>  #include <libcamera/base/object.h>
>
>  #include <libcamera/controls.h>
> @@ -88,7 +89,8 @@ private:
>
>  	const char *name_;
>
> -	bool lockOwner_;
> +	Mutex lock_;
> +	bool lockOwner_ LIBCAMERA_TSA_GUARDED_BY(lock_); /* *Not* ownership of lock_ */

Took me a while to find out what the comment means..

Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

Thanks
   j
>
>  	friend class PipelineHandlerFactory;
>  };
> diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
> index a9241ac62979..03e4b9e66aa6 100644
> --- a/src/libcamera/pipeline_handler.cpp
> +++ b/src/libcamera/pipeline_handler.cpp
> @@ -11,6 +11,7 @@
>  #include <sys/sysmacros.h>
>
>  #include <libcamera/base/log.h>
> +#include <libcamera/base/mutex.h>
>  #include <libcamera/base/utils.h>
>
>  #include <libcamera/camera.h>
> @@ -155,6 +156,8 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
>   */
>  bool PipelineHandler::lock()
>  {
> +	MutexLocker locker(lock_);
> +
>  	/* Do not allow nested locking in the same libcamera instance. */
>  	if (lockOwner_)
>  		return false;
> @@ -183,6 +186,8 @@ bool PipelineHandler::lock()
>   */
>  void PipelineHandler::unlock()
>  {
> +	MutexLocker locker(lock_);
> +
>  	if (!lockOwner_)
>  		return;
>
> --
> Regards,
>
> Laurent Pinchart
>