NSDistributedNotificationCenter class provides a way to send notifications to objects in other tasks. It takes
NSNotification objects and broadcasts them to any objects in other tasks that have registered for the notification with their task’s default distributed notification center.
- macOS 10.0+
Notification dispatch table. See “Class at a Glance” > “Principal Attributes” in
NotificationCenterfor information about the dispatch table.
In addition to the notification name and sender, dispatch table entries for distributed notification centers specify when the notification center delivers notifications to its observers. See the
postNotificationName(_:object:userInfo:deliverImmediately:)method, Suspending and Resuming Notification Delivery, and
Commonly Used Methods
Accesses the default distributed notification center.
Registers an object to receive a notification with a specified behavior when notification delivery is suspended.
Creates and posts a notification.
Specifies that an object no longer wants to receive certain notifications.
Each task has a default distributed notification center that you access with the
default() class method. There may be different types of distributed notification centers. Currently there is a single type—
NSLocalNotificationCenterType. This type of distributed notification center handles notifications that can be sent between tasks on a single computer. For communication between tasks on different computers, use Distributed Objects Programming Topics.
Posting a distributed notification is an expensive operation. The notification gets sent to a system-wide server that distributes it to all the tasks that have objects registered for distributed notifications. The latency between posting the notification and the notification’s arrival in another task is unbounded. In fact, when too many notifications are posted and the server’s queue fills up, notifications may be dropped.
Distributed notifications are delivered via a task’s run loop. A task must be running a run loop in one of the “common” modes, such as
NSDefaultRunLoopMode, to receive a distributed notification. For multithreaded applications running in macOS 10.3 and later, distributed notifications are always delivered to the main thread. For multithreaded applications running in OS X v10.2.8 and earlier, notifications are delivered to the thread that first used the distributed notifications API, which in most cases is the main thread.