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                                  dispatch_once(3)