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

[Tomi Valkeinen]

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.

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.

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