dispatch_walltime(3) Calculate temporal milestones

Other Alias



Fd #include <dispatch/dispatch.h> Vt static const dispatch_time_t DISPATCH_TIME_NOW = 0 ; Vt static const dispatch_time_t DISPATCH_TIME_FOREVER = ~0ull ; Ft dispatch_time_t Fo dispatch_time Fa dispatch_time_t base int64_t offset Fc Ft dispatch_time_t Fo dispatch_walltime Fa struct timespec *base int64_t offset Fc


The Fn dispatch_time and Fn dispatch_walltime functions provide a simple mechanism for expressing temporal milestones for use with dispatch functions that need timeouts or operate on a schedule.

The Fa dispatch_time_t type is a semi-opaque integer, with only the special values Vt DISPATCH_TIME_NOW and Vt 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 Fn dispatch_time function returns a milestone relative to an existing milestone after adding Fa offset nanoseconds. If the Fa base parameter maps internally to a wall clock, then the returned value is relative to the wall clock. Otherwise, if Fa base is Vt DISPATCH_TIME_NOW , then the the current time of the default host clock is used.

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


The Fn dispatch_time and Fn dispatch_walltime functions detect overflow and underflow conditions when applying the Fa offset parameter.

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

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


Create a milestone two seconds in the future:
milestone = dispatch_time(DISPATCH_TIME_NOW, 2LL * NSEC_PER_SEC);

Create a milestone for use as an infinite timeout:


Create a milestone on Tuesday, January 19, 2038:

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


These functions return an abstract value for use with Fn dispatch_after , Fn dispatch_group_wait , or Fn dispatch_semaphore_wait .