libcamera/base: Move extended base functionality

Move the functionality for the following components to the new
base support library:

 - BoundMethod
 - EventDispatcher
 - EventDispatcherPoll
 - Log
 - Message
 - Object
 - Signal
 - Semaphore
 - Thread
 - Timer

While it would be preferable to see these split to move one component
per commit, these components are all interdependent upon each other,
which leaves us with one big change performing the move for all of them.

Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 300 insertions, 0 deletions

diff --git a/src/libcamera/base/object.cpp b/src/libcamera/base/object.cpp
new file mode 100644
index 00000000..25410ecd
--- /dev/null
+++ b/src/libcamera/base/object.cpp
@@ -0,0 +1,300 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * object.cpp - Base object
+ */
+
+#include <libcamera/base/object.h>
+
+#include <algorithm>
+
+#include <libcamera/base/log.h>
+#include <libcamera/base/message.h>
+#include <libcamera/base/semaphore.h>
+#include <libcamera/base/signal.h>
+#include <libcamera/base/thread.h>
+#include <libcamera/base/utils.h>
+
+/**
+ * \file base/object.h
+ * \brief Base object to support automatic signal disconnection
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(Object)
+
+/**
+ * \class Object
+ * \brief Base object to support automatic signal disconnection
+ *
+ * The Object class simplifies signal/slot handling for classes implementing
+ * slots. By inheriting from Object, an object is automatically disconnected
+ * from all connected signals when it gets destroyed.
+ *
+ * Object instances are bound to the thread of their parent, or the thread in
+ * which they're created when they have no parent. When a message is posted to
+ * an object, its handler will run in the object's thread. This allows
+ * implementing easy message passing between threads by inheriting from the
+ * Object class.
+ *
+ * Deleting an object from a thread other than the one the object is bound to is
+ * unsafe, unless the caller ensures that the object isn't processing any
+ * message concurrently.
+ *
+ * Object slots connected to signals will also run in the context of the
+ * object's thread, regardless of whether the signal is emitted in the same or
+ * in another thread.
+ *
+ * \sa Message, Signal, Thread
+ */
+
+/**
+ * \brief Construct an Object instance
+ * \param[in] parent The object parent
+ *
+ * The new Object instance is bound to the thread of its \a parent, or to the
+ * current thread if the \a parent is nullptr.
+ */
+Object::Object(Object *parent)
+	: parent_(parent), pendingMessages_(0)
+{
+	thread_ = parent ? parent->thread() : Thread::current();
+
+	if (parent)
+		parent->children_.push_back(this);
+}
+
+/**
+ * \brief Destroy an Object instance
+ *
+ * Deleting an Object automatically disconnects all signals from the Object's
+ * slots. All the Object's children are made orphan, but stay bound to their
+ * current thread.
+ *
+ * Object instances shall be destroyed from the thread they are bound to,
+ * otherwise undefined behaviour may occur. If deletion of an Object needs to
+ * be scheduled from a different thread, deleteLater() shall be used.
+ */
+Object::~Object()
+{
+	/*
+	 * Move signals to a private list to avoid concurrent iteration and
+	 * deletion of items from Signal::disconnect().
+	 */
+	std::list<SignalBase *> signals(std::move(signals_));
+	for (SignalBase *signal : signals)
+		signal->disconnect(this);
+
+	if (pendingMessages_)
+		thread()->removeMessages(this);
+
+	if (parent_) {
+		auto it = std::find(parent_->children_.begin(),
+				    parent_->children_.end(), this);
+		ASSERT(it != parent_->children_.end());
+		parent_->children_.erase(it);
+	}
+
+	for (auto child : children_)
+		child->parent_ = nullptr;
+}
+
+/**
+ * \brief Schedule deletion of the instance in the thread it belongs to
+ *
+ * This function schedules deletion of the Object when control returns to the
+ * event loop that the object belongs to. This ensures the object is destroyed
+ * from the right context, as required by the libcamera threading model.
+ *
+ * If this function is called before the thread's event loop is started, the
+ * object will be deleted when the event loop starts.
+ *
+ * Deferred deletion can be used to control the destruction context with shared
+ * pointers. An object managed with shared pointers is deleted when the last
+ * reference is destroyed, which makes difficult to ensure through software
+ * design which context the deletion will take place in. With a custom deleter
+ * for the shared pointer using deleteLater(), the deletion can be guaranteed to
+ * happen in the thread the object is bound to.
+ *
+ * \code{.cpp}
+ * std::shared_ptr<MyObject> createObject()
+ * {
+ *     struct Deleter : std::default_delete<MyObject> {
+ *             void operator()(MyObject *obj)
+ *             {
+ *                     obj->deleteLater();
+ *             }
+ *     };
+ *
+ *     MyObject *obj = new MyObject();
+ *
+ *     return std::shared_ptr<MyObject>(obj, Deleter());
+ * }
+ * \endcode
+ *
+ * \context This function is \threadsafe.
+ */
+void Object::deleteLater()
+{
+	postMessage(std::make_unique<Message>(Message::DeferredDelete));
+}
+
+/**
+ * \brief Post a message to the object's thread
+ * \param[in] msg The message
+ *
+ * This method posts the message \a msg to the message queue of the object's
+ * thread, to be delivered to the object through the message() method in the
+ * context of its thread. Message ownership is passed to the thread, and the
+ * message will be deleted after being delivered.
+ *
+ * Messages are delivered through the thread's event loop. If the thread is not
+ * running its event loop the message will not be delivered until the event
+ * loop gets started.
+ *
+ * Due to their asynchronous nature, threads do not provide any guarantee that
+ * all posted messages are delivered before the thread is stopped. See
+ * \ref thread-stop for additional information.
+ *
+ * \context This function is \threadsafe.
+ */
+void Object::postMessage(std::unique_ptr<Message> msg)
+{
+	thread()->postMessage(std::move(msg), this);
+}
+
+/**
+ * \brief Message handler for the object
+ * \param[in] msg The message
+ *
+ * This virtual method receives messages for the object. It is called in the
+ * context of the object's thread, and can be overridden to process custom
+ * messages. The parent Object::message() method shall be called for any
+ * message not handled by the override method.
+ *
+ * The message \a msg is valid only for the duration of the call, no reference
+ * to it shall be kept after this method returns.
+ */
+void Object::message(Message *msg)
+{
+	switch (msg->type()) {
+	case Message::InvokeMessage: {
+		InvokeMessage *iMsg = static_cast<InvokeMessage *>(msg);
+		Semaphore *semaphore = iMsg->semaphore();
+		iMsg->invoke();
+
+		if (semaphore)
+			semaphore->release();
+
+		break;
+	}
+
+	case Message::DeferredDelete:
+		delete this;
+		break;
+
+	default:
+		break;
+	}
+}
+
+/**
+ * \fn R Object::invokeMethod()
+ * \brief Invoke a method asynchronously on an Object instance
+ * \param[in] func The object method to invoke
+ * \param[in] type Connection type for method invocation
+ * \param[in] args The method arguments
+ *
+ * This method invokes the member method \a func with arguments \a args, based
+ * on the connection \a type. Depending on the type, the method will be called
+ * synchronously in the same thread or asynchronously in the object's thread.
+ *
+ * Arguments \a args passed by value or reference are copied, while pointers
+ * are passed untouched. The caller shall ensure that any pointer argument
+ * remains valid until the method is invoked.
+ *
+ * Due to the asynchronous nature of threads, functions invoked asynchronously
+ * with the ConnectionTypeQueued type are not guaranteed to be called before
+ * the thread is stopped. See \ref thread-stop for additional information.
+ *
+ * \context This function is \threadsafe.
+ *
+ * \return For connection types ConnectionTypeDirect and
+ * ConnectionTypeBlocking, return the return value of the invoked method. For
+ * connection type ConnectionTypeQueued, return a default-constructed R value.
+ */
+
+/**
+ * \fn Object::thread()
+ * \brief Retrieve the thread the object is bound to
+ * \context This function is \threadsafe.
+ * \return The thread the object is bound to
+ */
+
+/**
+ * \brief Move the object and all its children to a different thread
+ * \param[in] thread The target thread
+ *
+ * This method moves the object and all its children from the current thread to
+ * the new \a thread.
+ *
+ * Before the object is moved, a Message::ThreadMoveMessage message is sent to
+ * it. The message() method can be reimplement in derived classes to be notified
+ * of the upcoming thread move and perform any required processing.
+ *
+ * Moving an object that has a parent is not allowed, and causes undefined
+ * behaviour.
+ *
+ * \context This function is thread-bound.
+ */
+void Object::moveToThread(Thread *thread)
+{
+	ASSERT(Thread::current() == thread_);
+
+	if (thread_ == thread)
+		return;
+
+	if (parent_) {
+		LOG(Object, Error)
+			<< "Moving object to thread with a parent is not permitted";
+		return;
+	}
+
+	notifyThreadMove();
+
+	thread->moveObject(this);
+}
+
+void Object::notifyThreadMove()
+{
+	Message msg(Message::ThreadMoveMessage);
+	message(&msg);
+
+	for (auto child : children_)
+		child->notifyThreadMove();
+}
+
+/**
+ * \fn Object::parent()
+ * \brief Retrieve the object's parent
+ * \return The object's parent
+ */
+
+void Object::connect(SignalBase *signal)
+{
+	signals_.push_back(signal);
+}
+
+void Object::disconnect(SignalBase *signal)
+{
+	for (auto iter = signals_.begin(); iter != signals_.end(); ) {
+		if (*iter == signal)
+			iter = signals_.erase(iter);
+		else
+			iter++;
+	}
+}
+
+} /* namespace libcamera */