[libcamera-devel] [PATCH v1 5/5] cam: Move request processing to main thread

[Laurent Pinchart]

Hi Marvin,

On Fri, Nov 13, 2020 at 01:35:40PM +0100, Marvin Schmidt wrote:
> Hey Laurent,
> 
> Thanks for your work
> 
> Am Fr., 13. Nov. 2020 um 07:38 Uhr schrieb Laurent Pinchart:
> >
> > The request completion handler is invoked in the camera manager thread,
> > which shouldn't be blocked for large amounts of time. As writing the
> > frames to disk can be a time-consuming process, move request processing
> > to the main thread by queueing an event to the event loop.
> >
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> >  src/cam/capture.cpp | 9 +++++++++
> >  src/cam/capture.h   | 1 +
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/src/cam/capture.cpp b/src/cam/capture.cpp
> > index 7580f798288c..43b109d099f6 100644
> > --- a/src/cam/capture.cpp
> > +++ b/src/cam/capture.cpp
> > @@ -157,6 +157,15 @@ void Capture::requestComplete(Request *request)
> >         if (request->status() == Request::RequestCancelled)
> >                 return;
> >
> > +       /*
> > +        * Defer processing of the completed request to the event loop, to avoid
> > +        * blocking the camera manager thread.
> > +        */
> > +       loop_->callLater(std::bind(&Capture::processRequest, this, request));
> 
> You could use a lambda here instead of std::bind:
> 
>     [=] { processRequest(request); }
> 
> std::bind would otherwise require including `<functional>`

<functional> is included by event_loop.h, as the callLater() function
takes an std::function parameter. But a lambda would certainly work. I
wonder, between std::bind and the proposed lambda function, what would
be more efficient ?

> > +}
> > +
> > +void Capture::processRequest(Request *request)
> > +{
> >         const Request::BufferMap &buffers = request->buffers();
> >
> >         /*
> > diff --git a/src/cam/capture.h b/src/cam/capture.h
> > index 45e5e8a9ba27..d21c95a26ce7 100644
> > --- a/src/cam/capture.h
> > +++ b/src/cam/capture.h
> > @@ -33,6 +33,7 @@ private:
> >         int capture(libcamera::FrameBufferAllocator *allocator);
> >
> >         void requestComplete(libcamera::Request *request);
> > +       void processRequest(libcamera::Request *request);
> >
> >         std::shared_ptr<libcamera::Camera> camera_;
> >         libcamera::CameraConfiguration *config_;

-- 
Regards,

Laurent Pinchart