: An execution of call_once
that does not call its func
An execution of call_once
that calls its func
is an active
An active execution calls
An exceptional execution propagates the exception to the caller of
Among all executions of call_once
for any given
: at most one is a returning execution; if there is a
returning execution, it is the last active execution; and there are
passive executions only if there is a returning execution.
executions allow other threads to reliably observe the results produced by the
earlier returning execution.
— end note