[libcamera-devel] [PATCH 4/5] libcamera: object: Document danger of deleting object from other thread

[Kieran Bingham]

Hi Laurent,

On 27/11/2019 08:49, Laurent Pinchart wrote:
> Object instances receive messages dispatched from the event loop of the
> thread they belong to. Deleting an object from a different thread is
> thus dangerous, unless the caller ensures that no message delivery is in
> progress. Document this in the Object class documentation.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/libcamera/object.cpp | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/src/libcamera/object.cpp b/src/libcamera/object.cpp
> index 1f787271f782..e76faf48b8ed 100644
> --- a/src/libcamera/object.cpp
> +++ b/src/libcamera/object.cpp
> @@ -40,6 +40,10 @@ LOG_DEFINE_CATEGORY(Object)
>   * implementing easy message passing between threads by inheriting from the
>   * Object class.
>   *
> + * Deleting an object from a thread other than the one the object is bound to is
> + * unsafe, unless the caller ensures that the object isn't processing any
> + * message concurrently.
> + *

What about codifying this with an assertion or Log(Error) check?

I.e. put something into the destructor which tests the current thread
against the object bound thread?

I think a runtime check here would be cheap, and serve a better way to
catch these bugs than simply documenting potential issues.

>   * Object slots connected to signals will also run in the context of the
>   * object's thread, regardless of whether the signal is emitted in the same or
>   * in another thread.
> 

-- 
Regards
--
Kieran