[#absl-Notification]
= xref:absl.adoc[absl]::Notification
:relfileprefix: ../
:mrdocs:

Lets threads wait for a single occurrence of a single event.

== Synopsis

Declared in `<absl/synchronization/notification.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class Notification;
----

== Description

The `Notification` object maintains a private boolean "notified" state that transitions to `true` at most once. The `Notification` class provides the following primary member functions: * `HasBeenNotified()` to query its state * `WaitForNotification*()` to have threads wait until the "notified" state is `true`. * `Notify()` to set the notification's "notified" state to `true` and notify all waiting threads that the event has occurred. This method may only be called once.

Note that while `Notify()` may only be called once, it is perfectly valid to call any of the `WaitForNotification*()` methods multiple times, from multiple threads ‐‐ even after the notification's "notified" state has been set ‐‐ in which case those methods will immediately return.

Note that the lifetime of a `Notification` requires careful consideration; it might not be safe to destroy a notification after calling `Notify()` since it is still legal for other threads to call `WaitForNotification*()` methods on the notification. However, observers responding to a "notified" state of `true` can safely delete the notification without interfering with the call to `Notify()` in the other thread.

Memory ordering: For any threads X and Y, if X calls `Notify()`, then any action taken by X before it calls `Notify()` is visible to thread Y after: * Y returns from `WaitForNotification()`, or * Y receives a `true` return value from either `HasBeenNotified()` or `WaitForNotificationWithTimeout()`.

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:absl/Notification/2constructor-01.adoc[`Notification`]         [.small]#[constructor]#
| Constructors
| xref:absl/Notification/2destructor.adoc[`~Notification`] [.small]#[destructor]#
| Destroys the notification.
| xref:absl/Notification/operator_assign.adoc[`operator=`]  [.small]#[deleted]#
| Deleted copy assignment; `Notification` is not copyable.
| xref:absl/Notification/HasBeenNotified.adoc[`HasBeenNotified`] 
| Queries the notification's "notified" state.
| xref:absl/Notification/Notify.adoc[`Notify`] 
| Sets the "notified" state to `true` and wakes waiting threads.
| xref:absl/Notification/WaitForNotification.adoc[`WaitForNotification`] 
| Blocks the calling thread until the notification is notified.
| xref:absl/Notification/WaitForNotificationWithDeadline.adoc[`WaitForNotificationWithDeadline`] 
| Blocks until the notification is notified or a deadline expires.
| xref:absl/Notification/WaitForNotificationWithTimeout.adoc[`WaitForNotificationWithTimeout`] 
| Blocks until the notification is notified or a timeout elapses.
|===



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