dispatch_once_f(3) osx man page | unix.com

dispatch_once(3)					   BSD Library Functions Manual 					  dispatch_once(3)

NAME
     dispatch_once -- execute a block only once

SYNOPSIS
     #include <dispatch/dispatch.h>

     void
     dispatch_once(dispatch_once_t *predicate, void (^block)(void));

     void
     dispatch_once_f(dispatch_once_t *predicate, void *context, void (*function)(void *));

DESCRIPTION
     The dispatch_once() function provides a simple and efficient mechanism to run an initializer exactly once, similar to pthread_once(3).  Well
     designed code hides the use of lazy initialization.  For example:

     FILE *getlogfile(void)
     {
	     static dispatch_once_t pred;
	     static FILE *logfile;

	     dispatch_once(&pred, ^{
		     logfile = fopen(MY_LOG_FILE, "a");
	     });

	     return logfile;
     }

FUNDAMENTALS
     The dispatch_once() function is a wrapper around dispatch_once_f().

SEE ALSO
     dispatch(3)

Darwin								    May 1, 2009 							    Darwin