[libcamera-devel] [PATCH 05/10] libcamera: request: Add support for fences

[Jacopo Mondi]

Hi Kieran,

On Tue, Nov 09, 2021 at 01:23:32PM +0000, Kieran Bingham wrote:
> Quoting Jacopo Mondi (2021-10-28 12:15:15)
> > Prepare the Request::Private class to handle fences by providing a
> > storage vector and interface functions to handle the number of pending
> > and expired fences.
> >
> > The intended user of the interface is the PipelineHandler class
> >
> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> >  include/libcamera/internal/request.h | 21 +++++++
> >  src/libcamera/request.cpp            | 89 +++++++++++++++++++++++++++-
> >  2 files changed, 109 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/libcamera/internal/request.h b/include/libcamera/internal/request.h
> > index df0cc014067e..2be4874756de 100644
> > --- a/include/libcamera/internal/request.h
> > +++ b/include/libcamera/internal/request.h
> > @@ -7,8 +7,12 @@
> >  #ifndef __LIBCAMERA_INTERNAL_REQUEST_H__
> >  #define __LIBCAMERA_INTERNAL_REQUEST_H__
> >
> > +#include <vector>
> > +
> >  #include <libcamera/request.h>
> >
> > +#include <libcamera/internal/fence.h>
> > +
> >  namespace libcamera {
> >
> >  class Camera;
> > @@ -24,9 +28,26 @@ public:
> >
> >         Camera *camera() const { return camera_; }
> >
> > +       unsigned int pendingFences() const { return pendingFences_; }
> > +       unsigned int expiredFences() const { return expiredFences_; }
> > +
> > +       void reuse();
> > +
> > +       std::vector<Fence> &fences() { return fences_; }
> > +       void addFence(Fence &&fence);
> > +       void clearFences();
> > +
> > +       void fenceExpired();
> > +       void fenceCompleted();
> > +
> >  private:
> >         Camera *camera_;
> >         bool cancelled_;
> > +
> > +       unsigned int pendingFences_ = 0;
> > +       unsigned int expiredFences_ = 0;
> > +
> > +       std::vector<Fence> fences_;
> >  };
> >
> >  } /* namespace libcamera */
> > diff --git a/src/libcamera/request.cpp b/src/libcamera/request.cpp
> > index 33fee1ac05ba..e88eee1fac36 100644
> > --- a/src/libcamera/request.cpp
> > +++ b/src/libcamera/request.cpp
> > @@ -63,6 +63,92 @@ Request::Private::~Private()
> >   * request hasn't been queued
> >   */
> >
> > +/**
> > + * \fn Request::Private::pendingFences()
> > + * \brief Retrieve the number of pending fences
> > + *
> > + * A Fence is pending if has not yet been signalled or it has not expired yet.
> > + *
> > + * \return The number of pending fences
> > + */
> > +
> > +/**
> > + * \fn Request::Private::expiredFences()
> > + * \brief Retrieve the number of expired fences
> > + * \return The number of expired fences
> > + */
> > +
> > +/**
> > + * \brief Reset the request for reuse
> > + */
> > +void Request::Private::reuse()
> > +{
> > +       cancelled_ = false;
> > +
> > +       fences_.clear();
> > +       pendingFences_ = 0;
> > +       expiredFences_ = 0;
> > +}
> > +
> > +/**
> > + * \fn Request::Private::fences()
> > + * \brief Retrieve a reference to the vector of pending fences
> > + * \return A reference to the vector of pending fences
> > + */
> > +
> > +/**
> > + * \brief Move a Fence into the Request
> > + *
> > + * Move a Fence into the Request and increase the pending fences
> > + * counter. The Fence is now stored into the Request and the original
> > + * one passed in as parameter is reset.
> > + *
> > + * Once the Fence completes, either because it is signalled or because
> > + * it has expired, the caller shall notify the Request about this by
> > + * calling fenceCompleted() or fenceExpired();
> > + */
> > +void Request::Private::addFence(Fence &&fence)
> > +{
> > +       fences_.push_back(std::move(fence));
> > +       pendingFences_++;
>
> Hrm ... I was expecting signals to be connected here ... but I guess
> that happens elsewhere...
>
>
> > +}
> > +
> > +/**
> > + * \brief Release all Fences stored in the request
> > + *
> > + * Clear the vector of fences in the Request by releasing all of them.
> > + * All Fences are closed and their file descriptors reset to 0.
> > + */
> > +void Request::Private::clearFences()
> > +{
> > +       ASSERT(!pendingFences_);
> > +       fences_.clear();
> > +}
> > +
> > +/**
> > + * \brief Notify that a Fence has been signalled
> > + *
> > + * Notify to the Request that a Fence has completed. This function decrease the
> > + * number of pending Fences in the request.
> > + */
> > +void Request::Private::fenceCompleted()
> > +{
> > +       pendingFences_--;
> > +}
> > +
> > +/**
> > + * \brief Notify that a Fence has expired
> > + *
> > + * Notify to the Request that a Fence has expired. This function decrease the
> > + * number of pending Fences in the request and increase the number of expired
> > + * ones.
> > + */
> > +void Request::Private::fenceExpired()
> > +{
> > +       expiredFences_++;
> > +       pendingFences_--;
>
> Are all these event driven counters thread safe? They may be, just seems
> a potential risk area...

My understanding is that slots are synchronous unless otherwise
specified.

As the Request::Private::fence*() functions are called from the
PipelineHandler::fenceCompleted() slot connected to Fence::complete
signal what happens is that
- Fence::activated() stops the timer
- Fence::timedout() disables the event notifier

so a single Fence::complete is emitted per Fence.

>From there we call the PipelineHandler::fenceCompleted() slot which is
run synchronously, hence I think we're safe.

Does this seems safe to you as well ?

Thanks
   j

>
>
> > +}
> > +
> >  /**
> >   * \enum Request::Status
> >   * Request completion status
> > @@ -158,10 +244,11 @@ void Request::reuse(ReuseFlag flags)
> >
> >         sequence_ = 0;
> >         status_ = RequestPending;
> > -       _d()->cancelled_ = false;
> >
> >         controls_->clear();
> >         metadata_->clear();
> > +
> > +       _d()->reuse();
> >  }
> >
> >  /**
> > --
> > 2.33.1
> >