libcamera: Add a poll-based event dispatcher

Provide a poll-based event dispatcher implementation as convenience for
applications that don't need a custom event loop. The poll-based
dispatcher is automatically instantiated if the application doesn't
provide its own dispatcher.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/include/event_dispatcher_poll.h

@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * event_dispatcher_poll.h - Poll-based event dispatcher
+ */
+#ifndef __LIBCAMERA_EVENT_DISPATCHER_POLL_H__
+#define __LIBCAMERA_EVENT_DISPATCHER_POLL_H__
+
+#include <libcamera/event_dispatcher.h>
+
+#include <list>
+#include <map>
+#include <vector>
+
+namespace libcamera {
+
+class EventNotifier;
+class Timer;
+
+class EventDispatcherPoll final : public EventDispatcher
+{
+public:
+	EventDispatcherPoll();
+	~EventDispatcherPoll();
+
+	void registerEventNotifier(EventNotifier *notifier);
+	void unregisterEventNotifier(EventNotifier *notifier);
+
+	void registerTimer(Timer *timer);
+	void unregisterTimer(Timer *timer);
+
+	void processEvents();
+
+private:
+	struct EventNotifierSetPoll {
+		short events() const;
+		EventNotifier *notifiers[3];
+	};
+
+	std::map<int, EventNotifierSetPoll> notifiers_;
+	std::list<Timer *> timers_;
+
+	void processNotifiers(std::vector<struct pollfd> &pollfds);
+	void processTimers();
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_EVENT_DISPATCHER_POLL_H__ */