py: Switch to non-blocking eventfd

Blocking wait can be easily implemented on top in Python, so rather than
supporting only blocking reads, or supporting both non-blocking and
blocking reads, let's support only non-blocking reads.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/py/examples/simple-cam.py

@@ -19,8 +19,9 @@ TIMEOUT_SEC = 3
 
 
 def handle_camera_event(cm):
-    # cm.get_ready_requests() will not block here, as we know there is an event
-    # to read.
+    # cm.get_ready_requests() returns the ready requests, which in our case
+    # should almost always return a single Request, but in some cases there
+    # could be multiple or none.
 
     reqs = cm.get_ready_requests()
 

src/py/examples/simple-capture.py

@@ -14,6 +14,7 @@
 
 import argparse
 import libcamera as libcam
+import selectors
 import sys
 
 # Number of frames to capture
@@ -107,11 +108,18 @@ def main():
     # The main loop. Wait for the queued Requests to complete, process them,
     # and re-queue them again.
 
+    sel = selectors.DefaultSelector()
+    sel.register(cm.event_fd, selectors.EVENT_READ)
+
     while frames_done < TOTAL_FRAMES:
-        # cm.get_ready_requests() blocks until there is an event and returns
-        # all the ready requests. Here we should almost always get a single
+        # cm.get_ready_requests() does not block, so we use a Selector to wait
+        # for a camera event. Here we should almost always get a single
         # Request, but in some cases there could be multiple or none.
 
+        events = sel.select()
+        if not events:
+            continue
+
         reqs = cm.get_ready_requests()
 
         for req in reqs:

src/py/examples/simple-continuous-capture.py

@@ -88,8 +88,9 @@ class CaptureContext:
     camera_contexts: list[CameraCaptureContext] = []
 
     def handle_camera_event(self):
-        # cm.get_ready_requests() will not block here, as we know there is an event
-        # to read.
+        # cm.get_ready_requests() returns the ready requests, which in our case
+        # should almost always return a single Request, but in some cases there
+        # could be multiple or none.
 
         reqs = self.cm.get_ready_requests()
 

src/py/libcamera/py_camera_manager.cpp

@@ -24,7 +24,7 @@ PyCameraManager::PyCameraManager()
 
 	cameraManager_ = std::make_unique<CameraManager>();
 
-	int fd = eventfd(0, EFD_CLOEXEC);
+	int fd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
 	if (fd == -1)
 		throw std::system_error(errno, std::generic_category(),
 					"Failed to create eventfd");
@@ -62,7 +62,13 @@ py::list PyCameraManager::cameras()
 
 std::vector<py::object> PyCameraManager::getReadyRequests()
 {
-	readFd();
+	int ret = readFd();
+
+	if (ret == -EAGAIN)
+		return std::vector<py::object>();
+
+	if (ret != 0)
+		throw std::system_error(-ret, std::generic_category());
 
 	std::vector<py::object> py_reqs;
 
@@ -96,12 +102,18 @@ void PyCameraManager::writeFd()
 		LOG(Python, Fatal) << "Unable to write to eventfd";
 }
 
-void PyCameraManager::readFd()
+int PyCameraManager::readFd()
 {
 	uint8_t buf[8];
 
-	if (read(eventFd_.get(), buf, 8) != 8)
-		throw std::system_error(errno, std::generic_category());
+	ssize_t ret = read(eventFd_.get(), buf, 8);
+
+	if (ret == 8)
+		return 0;
+	else if (ret < 0)
+		return -errno;
+	else
+		return -EIO;
 }
 
 void PyCameraManager::pushRequest(Request *req)

src/py/libcamera/py_camera_manager.h

@@ -39,7 +39,7 @@ private:
 		LIBCAMERA_TSA_GUARDED_BY(completedRequestsMutex_);
 
 	void writeFd();
-	void readFd();
+	int readFd();
 	void pushRequest(Request *req);
 	std::vector<Request *> getCompletedRequests();
 };

test/py/unittests.py

@@ -207,9 +207,16 @@ class SimpleCaptureMethods(CameraTesterBase):
         reqs = None
         gc.collect()
 
+        sel = selectors.DefaultSelector()
+        sel.register(cm.event_fd, selectors.EVENT_READ)
+
         reqs = []
 
         while True:
+            events = sel.select()
+            if not events:
+                continue
+
             ready_reqs = cm.get_ready_requests()
 
             reqs += ready_reqs