| CALL_ONCE(3C) | Standard C Library Functions | CALL_ONCE(3C) |
call_once — ensure
function is only called once
#include
<treads.h>
once_flag once = ONCE_FLAG_INIT;
void
call_once(once_flag *once,
void (*func)(void));
The
call_once()
function is used to ensure that an operation occurs only once, even across
multiple threads. Each instance of a properly initialized
once_flag can be passed to the
call_once function; however, only a single caller will
successfully execute the specified function, func.
This ensures that the argument func is called only
once. Note, the argument once is the only thing used
as a point of synchronization. If multiple callers use the same pointer for
once, but use different values for
func, then only one of the functions will be
successfully called.
The argument
once() should
always be initialized to the symbol
ONCE_FLAG_INIT
before calling call_once(). Failure to do so will
result in undefined behavior.
Like
pthread_once(3C), the
call_once()
function is not itself a cancellation point; however, if the thread calling
func()
encounters a cancellation point and is cancelled, then the value pointed to
by once will be as though
call_once() had not been called, as
func() had not completed successfully.
The call_once() function does not return
any values. Upon its completion, it is guaranteed that
func will have been called at most once across the
liftime of the once argument .
pthread_once(3C), threads.h(3HEAD), attributes(7), threads(7)
| February 17, 2023 | OmniOS |