1dispatch_once(3)         BSD Library Functions Manual         dispatch_once(3)
2

NAME

4     dispatch_once — execute a block only once
5

SYNOPSIS

7     #include <dispatch/dispatch.h>
8
9     void
10     dispatch_once(dispatch_once_t *predicate, void (^block)(void));
11
12     void
13     dispatch_once_f(dispatch_once_t *predicate, void *context,
14         void (*function)(void *));
15

DESCRIPTION

17     The dispatch_once() function provides a simple and efficient mechanism to
18     run an initializer exactly once, similar to pthread_once(3).  Well
19     designed code hides the use of lazy initialization.  For example:
20
21     FILE *getlogfile(void)
22     {
23             static dispatch_once_t pred;
24             static FILE *logfile;
25
26             dispatch_once(&pred, ^{
27                     logfile = fopen(MY_LOG_FILE, "a");
28             });
29
30             return logfile;
31     }
32

FUNDAMENTALS

34     The dispatch_once() function is a wrapper around dispatch_once_f().
35

SEE ALSO

37     dispatch(3)
38
39Darwin                            May 1, 2009                           Darwin