libcamera: event_notifier_poll: Fix notifier unregistration during event processing

An event notifier may be unregistered from its activated signal. This
can cause the notifiers set entry in notifiers_ to be deleted while
processNotifiers() is looping over the notifiers_ map, leading to
problems.

To fix this, add a flag to the EventNotifierPoll class to indicate that
event processing is in progress. If the flag is set, the notifiers_
entry is not deleted during notifier unregistration, but will be deleted
by the event processing loop.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/include/event_dispatcher_poll.h

@@ -45,6 +45,8 @@ private:
 	std::list<Timer *> timers_;
 	int eventfd_;
 
+	bool processingEvents_;
+
 	int poll(std::vector<struct pollfd> *pollfds);
 	void processInterrupt(const struct pollfd &pfd);
 	void processNotifiers(const std::vector<struct pollfd> &pollfds);