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


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 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.

    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 0 (null) 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 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:
    typedef std::deque<Notification::Ptr> NfQueue;
    struct WaitInfo
    {
        Notification::Ptr pNf;
        Event nfAvailable;
    };
    typedef std::deque<WaitInfo *> WaitQueue;

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


} // namespace Poco


#endif // Foundation_NotificationQueue_INCLUDED