cam: Add event loop

Add a simple event loop to the cam application and use it in the main()
function, with an example of how to handle SIGINT to gracefully stop the
loop.

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

src/cam/event_loop.cpp

@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * event_loop.cpp - cam - Event loop
+ */
+
+#include <libcamera/event_dispatcher.h>
+
+#include "event_loop.h"
+
+using namespace libcamera;
+
+EventLoop::EventLoop(EventDispatcher *dispatcher)
+	: dispatcher_(dispatcher)
+{
+}
+
+EventLoop::~EventLoop()
+{
+}
+
+int EventLoop::exec()
+{
+	exitCode_ = -1;
+	exit_.store(false, std::memory_order_release);
+
+	while (!exit_.load(std::memory_order_acquire))
+		dispatcher_->processEvents();
+
+	return exitCode_;
+}
+
+void EventLoop::exit(int code)
+{
+	exitCode_ = code;
+	exit_.store(true, std::memory_order_release);
+	dispatcher_->interrupt();
+}