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NotificationQueue.h
//
// NotificationQueue.h
//
// $Id: //poco/1.3/Foundation/include/Poco/NotificationQueue.h#2 $
//
// Library: Foundation
// Package: Notifications
// Module:  NotificationQueue
//
// Definition of the NotificationQueue class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#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;


00056 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;
00161       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

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