33 Concurrency support library [thread]

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.

stop_source, stop_token, and stop_callback implement semantics of shared ownership of a stop state.

Any stop_source, stop_token, or stop_callback that shares ownership of the same stop state is an associated stop_source, stop_token, or stop_callback, respectively.

The last remaining owner of the stop state automatically releases the resources associated with the stop state.

A stop_token can be passed to an operation which can either

• (3.1)
  actively poll the token to check if there has been a stop request, or
• (3.2)
  register a callback using the stop_callback class template which will be called in the event that a stop request is made.

A stop request made via a stop_source will be visible to all associated stop_token and stop_source objects.

Once a stop request has been made it cannot be withdrawn (a subsequent stop request has no effect).

Callbacks registered via a stop_callback object are called when a stop request is first made by any associated stop_source object.

Calls to the functions request_stop, stop_requested, and stop_possible do not introduce data races.

A call to request_stop that returns true synchronizes with a call to stop_requested on an associated stop_token or stop_source object that returns true.

Registration of a callback synchronizes with the invocation of that callback.