poco/Foundation/include/Poco/NotificationQueue.h

//
// NotificationQueue.h
//
// Library: Foundation
// Package: Notifications
// Module:  NotificationQueue
//
// Definition of the NotificationQueue class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_NotificationQueue_INCLUDED
#define Foundation_NotificationQueue_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Notification.h"
#include "Poco/Mutex.h"
#include "Poco/Event.h"
#include <deque>


namespace Poco {


class NotificationCenter;


class Foundation_API NotificationQueue
	/// A NotificationQueue object provides a way to implement asynchronous
	/// notifications. This is especially useful for sending notifications
	/// from one thread to another, for example from a background thread to
	/// the main (user interface) thread.
	///
	/// The NotificationQueue can also be used to distribute work from
	/// a controlling thread to one or more worker threads. Each worker thread
	/// repeatedly calls waitDequeueNotification() and processes the
	/// returned notification. Special care must be taken when shutting
	/// down a queue with worker threads waiting for notifications.
	/// The recommended sequence to shut down and destroy the queue is to
	///   1. set a termination flag for every worker thread
	///   2. call the wakeUpAll() method
	///   3. join each worker thread
	///   4. destroy the notification queue.
{
public:
	NotificationQueue();
		/// Creates the NotificationQueue.

	~NotificationQueue();
		/// Destroys the NotificationQueue.

	void enqueueNotification(Notification::Ptr pNotification);
		/// Enqueues the given notification by adding it to
		/// the end of the queue (FIFO).
		/// The queue takes ownership of the notification, thus
		/// a call like
		///     notificationQueue.enqueueNotification(new MyNotification);
		/// does not result in a memory leak.

	void enqueueUrgentNotification(Notification::Ptr pNotification);
		/// Enqueues the given notification by adding it to
		/// the front of the queue (LIFO). The event therefore gets processed
		/// before all other events already in the queue.
		/// The queue takes ownership of the notification, thus
		/// a call like
		///     notificationQueue.enqueueUrgentNotification(new MyNotification);
		/// does not result in a memory leak.

	Notification* dequeueNotification();
		/// Dequeues the next pending notification.
		/// Returns nullptr if no notification is available.
		/// The caller gains ownership of the notification and
		/// is expected to release it when done with it.
		///
		/// It is highly recommended that the result is immediately
		/// assigned to a Notification::Ptr, to avoid potential
		/// memory management issues.

	Notification* waitDequeueNotification();
		/// Dequeues the next pending notification.
		/// If no notification is available, waits for a notification
		/// to be enqueued.
		/// The caller gains ownership of the notification and
		/// is expected to release it when done with it.
		/// This method returns nullptr if wakeUpWaitingThreads()
		/// has been called by another thread.
		///
		/// It is highly recommended that the result is immediately
		/// assigned to a Notification::Ptr, to avoid potential
		/// memory management issues.

	Notification* waitDequeueNotification(long milliseconds);
		/// Dequeues the next pending notification.
		/// If no notification is available, waits for a notification
		/// to be enqueued up to the specified time.
		/// Returns 0 (null) if no notification is available.
		/// The caller gains ownership of the notification and
		/// is expected to release it when done with it.
		///
		/// It is highly recommended that the result is immediately
		/// assigned to a Notification::Ptr, to avoid potential
		/// memory management issues.

	void dispatch(NotificationCenter& notificationCenter);
		/// Dispatches all queued notifications to the given
		/// notification center.

	void wakeUpAll();
		/// Wakes up all threads that wait for a notification.

	bool empty() const;
		/// Returns true iff the queue is empty.

	int size() const;
		/// Returns the number of notifications in the queue.

	void clear();
		/// Removes all notifications from the queue.

	bool remove(Notification::Ptr pNotification);
		/// Removes a notification from the queue.
		/// Returns true if remove succeeded, false otherwise

	bool hasIdleThreads() const;
		/// Returns true if the queue has at least one thread waiting
		/// for a notification.

	static NotificationQueue& defaultQueue();
		/// Returns a reference to the default
		/// NotificationQueue.

protected:
	Notification::Ptr dequeueOne();

private:
	using NfQueue = std::deque<Notification::Ptr>;
	struct WaitInfo
	{
		Notification::Ptr pNf;
		Event             nfAvailable;
	};
	using WaitQueue = std::deque<WaitInfo *>;

	NfQueue           _nfQueue;
	WaitQueue         _waitQueue;
	mutable FastMutex _mutex;
};


} // namespace Poco


#endif // Foundation_NotificationQueue_INCLUDED