[RFC PATCH 2/4] libcamera: internal: Allow to limit the number of queued requests

[Jacopo Mondi]

Hi Sven, Stefan

On Tue, May 27, 2025 at 05:46:48PM +0200, Sven Püschel wrote:
> Hi Stefan,
>
> On 5/26/25 23:42, Stefan Klug wrote:
> > Allow pipeline handler classes to limit the maximum number of requests that
> > get queued using queueRequestDevice().
> >
> > Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> > ---
> >   include/libcamera/internal/pipeline_handler.h | 5 +++++
> >   src/libcamera/pipeline_handler.cpp            | 3 +++
> >   2 files changed, 8 insertions(+)
> >
> > diff --git a/include/libcamera/internal/pipeline_handler.h b/include/libcamera/internal/pipeline_handler.h
> > index dedc29e815fb..86b86d5971dc 100644
> > --- a/include/libcamera/internal/pipeline_handler.h
> > +++ b/include/libcamera/internal/pipeline_handler.h
> > @@ -79,6 +79,11 @@ protected:
> >   	virtual bool acquireDevice(Camera *camera);
> >   	virtual void releaseDevice(Camera *camera);
> > +	virtual unsigned int maxQueuedRequestsDevice() const
> > +	{
> > +		return std::numeric_limits<unsigned int>::max();
> > +	}
> > +
> is there a benefit of having a virtual function instead of a variable
> (initialized to max by default and potentially changed in the subclass
> constructors)?

Just for sake of discussion, should we go in the other direction and
make this a pure virtual function in the base class to make sure every
pipeline handler provides an implementation ?

> >   	CameraManager *manager_;
> >   private:
> > diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
> > index 14d8602e67d8..1853bca71371 100644
> > --- a/src/libcamera/pipeline_handler.cpp
> > +++ b/src/libcamera/pipeline_handler.cpp
> > @@ -490,6 +490,9 @@ void PipelineHandler::doQueueRequests()
> >   		Camera::Private *data = camera->_d();
> >   		while (!data->waitingRequests_.empty()) {
> > +			if (data->queuedRequests_.size() == maxQueuedRequestsDevice())
> > +				break;
> > +
> >   			Request *request = data->waitingRequests_.front();
> >   			if (!request->_d()->prepared_)
> >   				break;