| RUN_ONCE(9) | Kernel Developer's Manual | RUN_ONCE(9) |
RUN_ONCE, INIT_ONCE,
FINI_ONCE —
#include <sys/once.h>
ONCE_DECL(control);
int
RUN_ONCE(once_t
*control, int
(*init_func)(void));
int
INIT_ONCE(once_t
*control, int
(*init_func)(void));
void
FINI_ONCE(once_t
*control, void
(*fini_func)(void));
RUN_ONCE() provides a functionality similar to
pthread_once(3). It
ensures that, for a given control,
init_func() is executed (successfully) exactly once.
It is considered as a successful execution if and only if
init_func() returned 0. As long as there was no
successful execution, RUN_ONCE() will try again each
time it is called.
RUN_ONCE() can sleep if it's called
concurrently.
INIT_ONCE() is used in pair with
FINI_ONCE(). INIT_ONCE()
will only be run once similar to RUN_ONCE().
FINI_ONCE() will only be run at last time if it is
called as many times as calling INIT_ONCE(). When
FINI_ONCE() is executed, the next call to
INIT_ONCE() will be executed again. That is,
INIT_ONCE() and FINI_ONCE()
can be nested.
RUN_ONCE() returns what
init_func() returned. Otherwise, it returns 0.
RUN_ONCE() is used.
Regardless of how many times some_func() is executed,
init_func() will be executed exactly once.
static int
init_func(void)
{
/*
* do some initialization.
*/
return 0; /* success */
}
int
some_func(void)
{
static ONCE_DECL(control);
RUN_ONCE(&control, init_func);
/*
* we are sure that init_func has already been completed here.
*/
}
| March 19, 2019 | NetBSD 10.0 |