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[thread.stoptoken.intro]
32 Concurrency support library [thread]
32.3 Stop tokens [thread.stoptoken]
32.3.1 Introduction [thread.stoptoken.intro]
Subclause [thread.stoptoken] describes components that can be used to asynchronously request that an operation stops execution in a timely manner, typically because the result is no longer required.
Such a request is called a stop request.
The conceptsstoppable-source,stoppable_token, andstoppable-callback-for specify the required syntax and semantics of shared access to a stop state.
Any object modeling stoppable-source,stoppable_token, orstoppable-callback-for that refers to the same stop state is an associatedstoppable-source,stoppable_token, orstoppable-callback-for, respectively.
An object of a type that models stoppable_token can be passed to an operation that can either
actively poll the token to check if there has been a stop request, or
register a callback that will be called in the event that a stop request is made.
A stop request made via an object whose type models stoppable-source will be visible to all associated stoppable_token andstoppable-source objects.
Once a stop request has been made it cannot be withdrawn (a subsequent stop request has no effect).
Callbacks registered via an object whose type models stoppable-callback-for are called when a stop request is first made by any associated stoppable-source object.
The types stop_source and stop_token and the class template stop_callback implement the semantics of shared ownership of a stop state.
The last remaining owner of the stop state automatically releases the resources associated with the stop state.
An object of type inplace_stop_source is the sole owner of its stop state.
An object of type inplace_stop_token or of a specialization of the class template inplace_stop_callback does not participate in ownership of its associated stop state.
[Note 1:
They are for use when all uses of the associated token and callback objects are known to nest within the lifetime of the inplace_stop_source object.
â end note]