NetBSD/share/man/man9/RUN_ONCE.9

.\"	$NetBSD: RUN_ONCE.9,v 1.5 2006/01/17 00:14:16 wiz Exp $
.\"
.\" Copyright (c)2005 YAMAMOTO Takashi,
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.\" ------------------------------------------------------------
.Dd January 17, 2006
.Dt RUN_ONCE 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm RUN_ONCE
.Nd Run a function exactly once
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/once.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Vt ONCE_DECL(control);
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn RUN_ONCE \
"once_t *control" "int (*init_func)(void)"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
.Fn RUN_ONCE
provides a functionality similar to
.Fn pthread_once 3 .
It ensures that, for a given
.Fa control ,
.Fn init_func
is executed (successfully) exactly once.
It is considered as a successful execution if and only if
.Fn init_func
returned 0.
As long as there was no successful execution,
.Fn RUN_ONCE
will try again each time it is called.
.Pp
.Fn RUN_ONCE
can sleep if it's called concurrently.
.\" ------------------------------------------------------------
.Sh RETURN VALUES
On failure,
.Fn RUN_ONCE
returns what
.Fn init_func
returned.
Otherwise, it returns 0.
.\" ------------------------------------------------------------
.Sh EXAMPLES
The following example shows how
.Fn RUN_ONCE
is used.
Regardless of how many times
.Fn some_func
is executed,
.Fn init_func
will be executed exactly once.
.Bd -literal
static int
init_func(void)
{

	/*
	 * do some initialization.
	 */

	return 0; /* success */
}

int
some_func(void)
{
	static DECL_ONCE(control);

	RUN_ONCE(\*[Am]control, init_func);

	/*
	 * we are sure that init_func has already been completed here.
	 */
}
.Ed
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr pthread_once 3 ,
.Xr intro 9 ,
.Xr ltsleep 9