Time Management
The traditional abstraction of time in Mach is the clock, which provides a set
of asynchronous alarm services based on mach_timespec_t.
There are one or more clock objects, each defining a monotonically
increasing time value expressed in nanoseconds. The real-time clock
is built in, and is the most important, but there may be other clocks
for other notions of time in the system. Clocks support operations
to get the current time, sleep for a given period, set an alarm
(a notification that is sent at a given time), and so forth.
The mach_timespec_t API is deprecated
in Mac OS X. The newer and preferred API is based on timer objects
that in turn use AbsoluteTime as
the basic data type. AbsoluteTime is
a machine-dependent type, typically based on the platform-native
time base. Routines are provided to convert AbsoluteTime values
to and from other data types, such as nanoseconds. Timer objects
support asynchronous, drift-free notification, cancellation, and
premature alarms. They are more efficient and permit higher resolution
than clocks.
