The 'Time::HiRes' module implements a Perl interface to the 'usleep',
'nanosleep', 'ualarm', 'gettimeofday', and 'setitimer'/'getitimer' system
calls, in other words, high resolution time and timers. See the the
/EXAMPLES manpage section below and the test scripts for usage; see your
system documentation for the description of the underlying 'nanosleep' or
'usleep', 'ualarm', 'gettimeofday', and 'setitimer'/'getitimer' calls.

If your system lacks 'gettimeofday()' or an emulation of it you don't get
'gettimeofday()' or the one-argument form of 'tv_interval()'. If your
system lacks all of 'nanosleep()', 'usleep()', 'select()', and 'poll', you
don't get 'Time::HiRes::usleep()', 'Time::HiRes::nanosleep()', or
'Time::HiRes::sleep()'. If your system lacks both 'ualarm()' and
'setitimer()' you don't get 'Time::HiRes::ualarm()' or
'Time::HiRes::alarm()'.

If you try to import an unimplemented function in the 'use' statement it
will fail at compile time.