libcamera: thread: Add a messaging passing API

Create a new Message class to model a message that can be passed to an
object living in another thread. Only an invalid message type is
currently defined, more messages will be added in the future.

The Thread class is extended with a messages queue, and the Object class
with thread affinity.

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

1 files changed, 71 insertions, 0 deletions

diff --git a/src/libcamera/message.cpp b/src/libcamera/message.cpp
new file mode 100644
index 00000000..5bb17ae2
--- /dev/null
+++ b/src/libcamera/message.cpp
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * message.cpp - Message queue support
+ */
+
+#include "message.h"
+
+#include "log.h"
+
+/**
+ * \file message.h
+ * \brief Message queue support
+ *
+ * The messaging API enables inter-thread communication through message
+ * posting. Messages can be sent from any thread to any recipient deriving from
+ * the Object class.
+ *
+ * To post a message, the sender allocates it dynamically as instance of a class
+ * derived from Message. It then posts the message to an Object recipient
+ * through Object::postMessage(). Message ownership is passed to the object,
+ * thus the message shall not store any temporary data.
+ *
+ * The message is delivered in the context of the object's thread, through the
+ * Object::message() virtual method. After delivery the message is
+ * automatically deleted.
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(Message)
+
+/**
+ * \class Message
+ * \brief A message that can be posted to a Thread
+ */
+
+/**
+ * \enum Message::Type
+ * \brief The message type
+ * \var Message::None
+ * \brief Invalid message type
+ */
+
+/**
+ * \brief Construct a message object of type \a type
+ * \param[in] type The message type
+ */
+Message::Message(Message::Type type)
+	: type_(type)
+{
+}
+
+Message::~Message()
+{
+}
+
+/**
+ * \fn Message::type()
+ * \brief Retrieve the message type
+ * \return The message type
+ */
+
+/**
+ * \fn Message::receiver()
+ * \brief Retrieve the message receiver
+ * \return The message receiver
+ */
+
+}; /* namespace libcamera */