[libcamera-devel] [RFC v1 5/7] py: Add 'nonblocking' argument to get_ready_requests()

[Kieran Bingham]

Quoting Tomi Valkeinen (2022-06-23 15:47:34)
> Add 'nonblocking' argument to get_ready_requests() which allows the user
> to ensure get_ready_requests() never blocks. This can be used e.g. after
> calling camera.stop(), to process or discard any ready or cancelled
> Requests.

I guess I needed to read ahead for the comments I posted on the previous
patch ;-)

> 
> In fact, it probably should always be used after stopping the cameras,
> unless you have made sure that there are no unprocessed Requests. If you
> start the camera again, and you have left Requests unprocessed, you will
> get those "old" Requests when you expect to get the new Requests.
> 
> It may be good to call this even if your script exits after stopping
> the cameras, as unprocessed Requests will keep the Cameras and related
> objects alive, and thus they won't be freed. As your script is exiting
> it's strictly speaking not an issue, but it does make tracking other
> "real" memory leaks more difficult.
> 
> Perhaps the camera.start() should go and discard any old Requests
> related to that camera. For the exit issue I don't see any automatic
> solution.

At the end of camera.stop() we should validate and ensure that all
Requests are released to the application. We should hold no internal
requests when camera.stop() completes.

I.e. ... if we have things to discard at camera.start() - that's a bug I
believe.

ahhh but here perhaps the issue is that the python code is the one that
has to 'retrieve' those, while in C++ they are returned via a signal?

Is there any harm in discarding the requests at the end of camera.stop()
such that there is simply 'nothing left to process' after? Or does the
python application have to end up owning the requests to correctly
release them?


> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> ---
>  src/py/libcamera/py_camera_manager.cpp | 21 +++++++++++++++++++--
>  src/py/libcamera/py_camera_manager.h   |  4 +++-
>  src/py/libcamera/py_main.cpp           |  3 ++-
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/src/py/libcamera/py_camera_manager.cpp b/src/py/libcamera/py_camera_manager.cpp
> index c9e5a99c..ba45f713 100644
> --- a/src/py/libcamera/py_camera_manager.cpp
> +++ b/src/py/libcamera/py_camera_manager.cpp
> @@ -5,6 +5,7 @@
>  
>  #include "py_camera_manager.h"
>  
> +#include <poll.h>
>  #include <sys/eventfd.h>
>  #include <unistd.h>
>  
> @@ -55,9 +56,10 @@ py::list PyCameraManager::getCameras()
>         return l;
>  }
>  
> -std::vector<py::object> PyCameraManager::getReadyRequests()
> +std::vector<py::object> PyCameraManager::getReadyRequests(bool nonBlocking)
>  {
> -       readFd();
> +       if (!nonBlocking || hasEvents())
> +               readFd();
>  
>         std::vector<Request *> v;
>         getRequests(v);
> @@ -113,3 +115,18 @@ void PyCameraManager::getRequests(std::vector<Request *> &v)
>         std::lock_guard guard(reqlist_mutex_);
>         swap(v, reqList_);
>  }
> +
> +bool PyCameraManager::hasEvents()
> +{
> +       struct pollfd pfd = {
> +               .fd = eventFd_,
> +               .events = POLLIN,
> +               .revents = 0,
> +       };
> +
> +       int ret = poll(&pfd, 1, 0);
> +       if (ret == -1)
> +               throw std::system_error(errno, std::generic_category());
> +
> +       return pfd.revents & POLLIN;
> +}
> diff --git a/src/py/libcamera/py_camera_manager.h b/src/py/libcamera/py_camera_manager.h
> index b0b971ad..2396d236 100644
> --- a/src/py/libcamera/py_camera_manager.h
> +++ b/src/py/libcamera/py_camera_manager.h
> @@ -23,7 +23,7 @@ public:
>  
>         int eventFd() const { return eventFd_; }
>  
> -       std::vector<pybind11::object> getReadyRequests();
> +       std::vector<pybind11::object> getReadyRequests(bool nonBlocking = false);
>  
>         void handleRequestCompleted(Request *req);
>  
> @@ -36,4 +36,6 @@ private:
>         void readFd();
>         void pushRequest(Request *req);
>         void getRequests(std::vector<Request *> &v);
> +
> +       bool hasEvents();
>  };
> diff --git a/src/py/libcamera/py_main.cpp b/src/py/libcamera/py_main.cpp
> index 23018288..ee4ecb9b 100644
> --- a/src/py/libcamera/py_main.cpp
> +++ b/src/py/libcamera/py_main.cpp
> @@ -103,7 +103,8 @@ PYBIND11_MODULE(_libcamera, m)
>                 .def_property_readonly("cameras", &PyCameraManager::getCameras)
>  
>                 .def_property_readonly("event_fd", &PyCameraManager::eventFd)
> -               .def("get_ready_requests", &PyCameraManager::getReadyRequests);
> +               .def("get_ready_requests", &PyCameraManager::getReadyRequests,
> +                    py::arg("nonblocking") = false);
>  
>         pyCamera
>                 .def_property_readonly("id", &Camera::id)
> -- 
> 2.34.1
>