libcamera: Add event notification infrastructure

Add three new classes, EventDispatcher, EventNotifier and Timer, that
define APIs for file descriptor event notification and timers. The
implementation of the EventDispatcher is meant to be provided to
libcamera by the application.

The event dispatcher is integrated twith the camera manager to implement
automatic registration of timers and events.

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

src/libcamera/timer.cpp

@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * timer.cpp - Generic timer
+ */
+
+#include <time.h>
+
+#include <libcamera/camera_manager.h>
+#include <libcamera/event_dispatcher.h>
+#include <libcamera/timer.h>
+
+#include "log.h"
+
+/**
+ * \file timer.h
+ * \brief Generic timer
+ */
+
+namespace libcamera {
+
+/**
+ * \class Timer
+ * \brief Single-shot timer interface
+ *
+ * The Timer class models a single-shot timer that is started with start() and
+ * emits the \ref timeout signal when it times out.
+ *
+ * Once started the timer will run until it times out. It can be stopped with
+ * stop(), and once it times out or is stopped, can be started again with
+ * start().
+ */
+
+/**
+ * \brief Construct a timer
+ */
+Timer::Timer()
+{
+}
+
+/**
+ * \brief Start or restart the timer with a timeout of \a msec
+ * \param msec The timer duration in milliseconds
+ *
+ * If the timer is already running it will be stopped and restarted.
+ */
+void Timer::start(unsigned int msec)
+{
+	struct timespec tp;
+	clock_gettime(CLOCK_MONOTONIC, &tp);
+
+	interval_ = msec;
+	deadline_ = tp.tv_sec * 1000000000ULL + tp.tv_nsec + msec * 1000000;
+
+	LOG(Debug) << "Starting timer " << this << " with interval " << msec
+		   << ": deadline " << deadline_;
+
+	CameraManager::instance()->eventDispatcher()->registerTimer(this);
+}
+
+/**
+ * \brief Stop the timer
+ *
+ * After this function returns the timer is guaranteed not to emit the
+ * \ref timeout signal.
+ *
+ * If the timer is not running this function performs no operation.
+ */
+void Timer::stop()
+{
+	CameraManager::instance()->eventDispatcher()->unregisterTimer(this);
+
+	deadline_ = 0;
+}
+
+/**
+ * \brief Check if the timer is running
+ * \return True if the timer is running, false otherwise
+ */
+bool Timer::isRunning() const
+{
+	return deadline_ != 0;
+}
+
+/**
+ * \fn Timer::interval()
+ * \brief Retrieve the timer interval
+ * \return The timer interval in milliseconds
+ */
+
+/**
+ * \fn Timer::deadline()
+ * \brief Retrieve the timer deadline
+ * \return The timer deadline in nanoseconds
+ */
+
+/**
+ * \var Timer::timeout
+ * \brief Signal emitted when the timer times out
+ *
+ * The timer pointer is passed as a parameter.
+ */
+
+} /* namespace libcamera */