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()