cpp/thread/stop source/request stop

Issues a stop request to the stop-state, if the object has a stop-state and it has not yet already had stop requested.

The determination is made atomically, and if stop was requested, the stop-state is atomically updated to avoid race conditions, such that: However, see the Notes section.
 * and can be concurrently invoked on other s and s of the same stop-state;
 * can be concurrently invoked on other objects, and only one will actually perform the stop request.

Parameters
(none)

Return value
if the object has a stop-state and this invocation made a stop request, otherwise.

Postconditions
is or  is.