dispatch_once(3) [osx man page]

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

dispatch_after(3)					   BSD Library Functions Manual 					 dispatch_after(3)

NAME

     dispatch_after -- schedule blocks for deferred execution

SYNOPSIS

     #include <dispatch/dispatch.h>

     void
     dispatch_after(dispatch_time_t when, dispatch_queue_t queue, void (^block)(void));

     void
     dispatch_after_f(dispatch_time_t when, dispatch_queue_t queue, void *context, void (*function)(void *));

DESCRIPTION

     The dispatch_after() function submits the block to the given queue at the time specified by the when parameter.  The when parameter is a
     value created by dispatch_time() or dispatch_walltime().

     For a more detailed description about submitting blocks to queues, see dispatch_async(3).

CAVEATS

     dispatch_after() retains the passed queue.

     Specifying DISPATCH_TIME_NOW as the when parameter is supported, but is not as efficient as calling dispatch_async().

     The result of passing DISPATCH_TIME_FOREVER as the when parameter is undefined.

FUNDAMENTALS

     The dispatch_after() function is a wrapper around dispatch_after_f().

SEE ALSO

     dispatch(3), dispatch_async(3), dispatch_time(3)

Darwin								    May 1, 2009 							    Darwin