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)