[libcamera-devel] [PATCH v3 1/2] cam: event_loop: Stop queuing calls when the event loop are exiting

[Niklas Söderlund]

Terminating the event loop with EventLoop::exit() does not grantee that
it will terminate. If the event loops 'call later' queue can be kept
non-empty by continuously queuing new calls using EventLoop::callLater()
either from a different thread or from callbacks in the loop itself
EventLoop::dispatchCalls() will never complete and the loop will run
forever.

Solve this by only executing the already queued calls each invocation of
dispatchCalls() and only enter the idle loop if dispatchCalls() had no
calls to dispatch.

Reported-by: Sebastian Fricke <sebastian.fricke at posteo.net>
Fixes: f49e93338b6309a6 ("cam: event_loop: Add deferred calls support")
Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
 src/cam/event_loop.cpp | 21 +++++++++------------
 src/cam/event_loop.h   |  2 +-
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/src/cam/event_loop.cpp b/src/cam/event_loop.cpp
index 94c5d1d362455f33..f0b1ecbb6244c40a 100644
--- a/src/cam/event_loop.cpp
+++ b/src/cam/event_loop.cpp
@@ -41,8 +41,8 @@ int EventLoop::exec()
 	exit_.store(false, std::memory_order_release);
 
 	while (!exit_.load(std::memory_order_acquire)) {
-		dispatchCalls();
-		event_base_loop(event_, EVLOOP_NO_EXIT_ON_EMPTY);
+		if (!dispatchCalls())
+			event_base_loop(event_, EVLOOP_NO_EXIT_ON_EMPTY);
 	}
 
 	return exitCode_;
@@ -70,17 +70,14 @@ void EventLoop::callLater(const std::function<void()> &func)
 	interrupt();
 }
 
-void EventLoop::dispatchCalls()
+bool EventLoop::dispatchCalls()
 {
-	std::unique_lock<std::mutex> locker(lock_);
+	lock_.lock();
+	std::list<std::function<void()>> calls = std::move(calls_);
+	lock_.unlock();
 
-	for (auto iter = calls_.begin(); iter != calls_.end(); ) {
-		std::function<void()> call = std::move(*iter);
-
-		iter = calls_.erase(iter);
-
-		locker.unlock();
+	for (std::function<void()> call : calls)
 		call();
-		locker.lock();
-	}
+
+	return !calls.empty();
 }
diff --git a/src/cam/event_loop.h b/src/cam/event_loop.h
index 408073c50594d09d..b2535f7bdd96742a 100644
--- a/src/cam/event_loop.h
+++ b/src/cam/event_loop.h
@@ -38,7 +38,7 @@ private:
 	std::mutex lock_;
 
 	void interrupt();
-	void dispatchCalls();
+	bool dispatchCalls();
 };
 
 #endif /* __CAM_EVENT_LOOP_H__ */
-- 
2.30.0