dispatch_time(3)         BSD Library Functions Manual         dispatch_time(3)

NAME
     dispatch_time, dispatch_walltime -- Calculate temporal milestones

SYNOPSIS
     #include <dispatch/dispatch.h>

     static const dispatch_time_t DISPATCH_TIME_NOW = 0ull;
     static const dispatch_time_t DISPATCH_TIME_FOREVER = ~0ull;

     dispatch_time_t
     dispatch_time(dispatch_time_t base, int64_t offset);

     dispatch_time_t
     dispatch_walltime(struct timespec *base, int64_t offset);

DESCRIPTION
     The dispatch_time() and dispatch_walltime() functions provide a simple
     mechanism for expressing temporal milestones for use with dispatch func-
     tions that need timeouts or operate on a schedule.

     The dispatch_time_t type is a semi-opaque integer, with only the special
     values DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER being externally
     defined. All other values are represented using an internal format that
     is not safe for integer arithmetic or comparison.  The internal format is
     subject to change.

     The dispatch_time() function returns a milestone relative to an existing
     milestone after adding offset nanoseconds.  If the base parameter maps
     internally to a wall clock, then the returned value is relative to the
     wall clock.  Otherwise, if base is DISPATCH_TIME_NOW, then the current
     time of the default host clock is used.

     The dispatch_walltime() function is useful for creating a milestone rela-
     tive to a fixed point in time using the wall clock, as specified by the
     optional base parameter. If base is NULL, then the current time of the
     wall clock is used.

EDGE CONDITIONS
     The dispatch_time() and dispatch_walltime() functions detect overflow and
     underflow conditions when applying the offset parameter.

     Overflow causes DISPATCH_TIME_FOREVER to be returned. When base is
     DISPATCH_TIME_FOREVER, then the offset parameter is ignored.

     Underflow causes the smallest representable value to be returned for a
     given clock.

EXAMPLES
     Create a milestone two seconds in the future:

           milestone = dispatch_time(DISPATCH_TIME_NOW, 2 * NSEC_PER_SEC);

     Create a milestone for use as an infinite timeout:

           milestone = DISPATCH_TIME_FOREVER;

     Create a milestone on Tuesday, January 19, 2038:

           struct timespec ts;
           ts.tv_sec = 0x7FFFFFFF;
           ts.tv_nsec = 0;
           milestone = dispatch_walltime(&ts, 0);

     Use a negative delta to create a milestone an hour before the one above:

           milestone = dispatch_walltime(&ts, -60 * 60 * NSEC_PER_SEC);

RETURN VALUE
     These functions return an abstract value for use with dispatch_after(),
     dispatch_group_wait(), dispatch_semaphore_wait(), or
     dispatch_source_set_timer().

SEE ALSO
     dispatch(3), dispatch_after(3), dispatch_group_create(3),
     dispatch_semaphore_create(3)

Darwin                            May 1, 2009                           Darwin