dispatch_once(3)           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