Description

   The usleep function suspends the current process from execution
   for the number of microseconds specified by the mseconds
   argument. This argument must be less than 1,000,000. However,
   if its value is 0, then the call has no effect.

   Be aware that usleep time specifications are rounded up
   approximately to the next millisecond because that is the finest
   time interval granularity possible on OpenVMS systems.

   There is one real-time interval timer for each process. The
   usleep function does not interfere with a previous setting of
   this timer. If the process set this timer before calling usleep
   and if the time specified by mseconds equals or exceeds the
   interval timer's prior setting, then the process is awakened
   shortly before the timer was set to expire.