ClickHouse/base/poco/Foundation/include/Poco/PriorityNotificationQueue.h

//
// PriorityNotificationQueue.h
//
// Library: Foundation
// Package: Notifications
// Module:  PriorityNotificationQueue
//
// Definition of the PriorityNotificationQueue class.
//
// Copyright (c) 2009, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_PriorityNotificationQueue_INCLUDED
#define Foundation_PriorityNotificationQueue_INCLUDED


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


namespace Poco
{


class NotificationCenter;


class Foundation_API PriorityNotificationQueue
/// A PriorityNotificationQueue 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 PriorityNotificationQueue is quite similar to the NotificationQueue class.
/// The only difference to NotificationQueue is that each Notification is tagged
/// with a priority value. When inserting a Notification into the queue, the
/// Notification is inserted according to the given priority value, with
/// lower priority values being inserted before higher priority
/// values. Therefore, the lower the numerical priority value, the higher
/// the actual notification priority.
///
/// Notifications are dequeued in order of their priority.
///
/// The PriorityNotificationQueue 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:
    PriorityNotificationQueue();
    /// Creates the PriorityNotificationQueue.

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

    void enqueueNotification(Notification::Ptr pNotification, int priority);
    /// Enqueues the given notification by adding it to
    /// the queue according to the given priority.
    /// Lower priority values are inserted before higher priority values.
    /// The queue takes ownership of the notification, thus
    /// a call like
    ///     notificationQueue.enqueueNotification(new MyNotification, 1);
    /// 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 wakeUpAll()
    /// 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 PriorityNotificationQueue & defaultQueue();
    /// Returns a reference to the default
    /// PriorityNotificationQueue.

protected:
    Notification::Ptr dequeueOne();

private:
    typedef std::multimap<int, 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_PriorityNotificationQueue_INCLUDED