RUN_ONCE(9)						   BSD Kernel Developer's Manual					       RUN_ONCE(9)

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 execu-
     tion, 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)

BSD
								   July 7, 2010 							       BSD