NAME

RUN_ONCE — Run a function exactly once

SYNOPSIS

#include <sys/once.h>

ONCE_DECL(control);

int
RUN_ONCE(once_t *control, int (*init_func)(void));

DESCRIPTION

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.

RETURN VALUES

On failure, RUN_ONCE() returns what init_func() returned. Otherwise, it returns 0.

EXAMPLES

The following example shows how 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. 
	 */ 
}

SEE ALSO

pthread_once(3), condvar(9), intro(9)