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>

1 files changed, 121 insertions, 0 deletions

diff --git a/src/libcamera/event_notifier.cpp b/src/libcamera/event_notifier.cpp
new file mode 100644
index 00000000..71775a9c
--- /dev/null
+++ b/src/libcamera/event_notifier.cpp
@@ -0,0 +1,121 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * event_notifier.cpp - File descriptor event notifier
+ */
+
+#include <libcamera/camera_manager.h>
+#include <libcamera/event_dispatcher.h>
+#include <libcamera/event_notifier.h>
+
+/**
+ * \file event_notifier.h
+ * \brief File descriptor event notifier
+ */
+
+namespace libcamera {
+
+/**
+ * \class EventNotifier
+ * \brief Notify of activity on a file descriptor
+ *
+ * The EventNotifier models a file descriptor event source that can be
+ * monitored. It is created with the file descriptor to be monitored and the
+ * type of event, and is enabled by default. It will emit the \ref activated
+ * signal whenever an event of the monitored type occurs on the file descriptor.
+ *
+ * Supported type of events are EventNotifier::Read, EventNotifier::Write and
+ * EventNotifier::Exception. The type is specified when constructing the
+ * notifier, and can be retrieved using the type() function. To listen to
+ * multiple event types on the same file descriptor multiple notifiers must be
+ * created.
+ *
+ * The notifier can be disabled with the setEnable() function. When the notifier
+ * is disabled it ignores events and does not emit the \ref activated signal.
+ * The notifier can then be re-enabled with the setEnable() function.
+ *
+ * Creating multiple notifiers of the same type for the same file descriptor is
+ * not allowed and results in undefined behaviour.
+ *
+ * Notifier events are detected and dispatched from the
+ * EventDispatcher::processEvents() function.
+ */
+
+/**
+ * \enum EventNotifier::Type
+ * Type of file descriptor event to listen for.
+ * \var EventNotifier::Read
+ * Data is available to be read from the file descriptor
+ * \var EventNotifier::Write
+ * Data can be written to the file descriptor
+ * \var EventNotifier::Exception
+ * An exception has occurred on the file descriptor
+ */
+
+/**
+ * \brief Construct an event notifier with a file descriptor and event type
+ * \param fd The file descriptor to monitor
+ * \param type The event type to monitor
+ */
+EventNotifier::EventNotifier(int fd, Type type)
+	: fd_(fd), type_(type), enabled_(false)
+{
+	setEnabled(true);
+}
+
+EventNotifier::~EventNotifier()
+{
+	setEnabled(false);
+}
+
+/**
+ * \fn EventNotifier::type()
+ * \brief Retrieve the type of the event being monitored
+ * \return The type of the event
+ */
+
+/**
+ * \fn EventNotifier::fd()
+ * \brief Retrieve the file descriptor being monitored
+ * \return The file descriptor
+ */
+
+/**
+ * \fn EventNotifier::enabled()
+ * \brief Retrieve the notifier state
+ * \return True if the notifier is enabled, or false otherwise
+ * \sa setEnable()
+ */
+
+/**
+ * \brief Enable or disable the notifier
+ * \param enable True to enable the notifier, false to disable it
+ *
+ * This function enables or disables the notifier. A disabled notifier ignores
+ * events and does not emit the \ref activated signal.
+ */
+void EventNotifier::setEnabled(bool enable)
+{
+	if (enabled_ == enable)
+		return;
+
+	enabled_ = enable;
+
+	EventDispatcher *dispatcher = CameraManager::instance()->eventDispatcher();
+	if (enable)
+		dispatcher->registerEventNotifier(this);
+	else
+		dispatcher->unregisterEventNotifier(this);
+}
+
+/**
+ * \var EventNotifier::activated
+ * \brief Signal emitted when the event occurs
+ *
+ * This signal is emitted when the event \ref type() occurs on the file
+ * descriptor monitored by the notifier. The notifier pointer is passed as a
+ * parameter.
+ */
+
+} /* namespace libcamera */