class Poco::NotificationQueue

Overview

A NotificationQueue object provides a way to implement asynchronous notifications. More…

#include <NotificationQueue.h>

class NotificationQueue
{
public:
    // structs

    struct WaitInfo;

    // methods

    void
    enqueueNotification(Notification::Ptr pNotification);

    void
    enqueueUrgentNotification(Notification::Ptr pNotification);

    Notification*
    dequeueNotification();

    Notification*
    waitDequeueNotification();

    Notification*
    waitDequeueNotification(long milliseconds);

    void
    dispatch(NotificationCenter& notificationCenter);

    void
    wakeUpAll();

    bool
    empty() const;

    int
    size() const;

    void
    clear();

    bool
    hasIdleThreads() const;

    static
    NotificationQueue&
    defaultQueue();

protected:
    // methods

    Notification::Ptr
    dequeueOne();
};

Detailed Documentation

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.

Construction

~NotificationQueue()

Destroys the NotificationQueue.

Methods

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.