[libcamera-devel] [PATCH 2/2] cam: Fix capturing an precis number of requests

[Niklas Söderlund]

When moving request processing from the camera manager thread to the
main thread a subtle race condition where added when running with the
--capture=N option.

Before the change the check of how many request had been queued was ran
in the camera manager thread and thus could not race with the producer
thread. After the change if requests are completed faster then they are
consumed (the consumer writes them to disk for example) the check may be
delayed and more then the expected number of request may be asked to
processed.

Sebastian Fricke <sebastian.fricke at posteo.net>
Fixes: 02eae70e15bdbb24 ("cam: Move request processing to main thread")
Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
 src/cam/capture.cpp | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/cam/capture.cpp b/src/cam/capture.cpp
index 113ea49d50046e5b..ef1601c716bfa137 100644
--- a/src/cam/capture.cpp
+++ b/src/cam/capture.cpp
@@ -157,6 +157,12 @@ void Capture::requestComplete(Request *request)
 	if (request->status() == Request::RequestCancelled)
 		return;
 
+	captureCount_++;
+	if (captureLimit_ && captureCount_ > captureLimit_) {
+		loop_->exit(0);
+		return;
+	}
+
 	/*
 	 * Defer processing of the completed request to the event loop, to avoid
 	 * blocking the camera manager thread.
@@ -206,12 +212,6 @@ void Capture::processRequest(Request *request)
 
 	std::cout << info.str() << std::endl;
 
-	captureCount_++;
-	if (captureLimit_ && captureCount_ >= captureLimit_) {
-		loop_->exit(0);
-		return;
-	}
-
 	request->reuse(Request::ReuseBuffers);
 	camera_->queueRequest(request);
 }
-- 
2.30.0