NAME

       usleep - suspend execution for an interval

SYNOPSIS

       #include <unistd.h>

       int usleep(useconds_t useconds);

DESCRIPTION

       The  usleep()  function  shall  cause  the calling thread to be suspended from execution until either the
       number of realtime microseconds specified by the argument useconds has elapsed or a signal  is  delivered
       to the calling thread and its action is to invoke a signal-catching function or to terminate the process.
       The suspension time may be longer than requested due to the scheduling of other activity by the system.

       The useconds argument shall be less than one million. If the value of useconds is 0, then the call has no
       effect.

       If  a SIGALRM signal is generated for the calling process during execution of usleep() and if the SIGALRM
       signal is being ignored or blocked from delivery, it is unspecified whether  usleep()  returns  when  the
       SIGALRM  signal  is  scheduled. If the signal is being blocked, it is also unspecified whether it remains
       pending after usleep() returns or it is discarded.

       If a SIGALRM signal is generated for the calling process during execution of usleep(), except as a result
       of a prior call to alarm(), and if the SIGALRM signal is not being ignored or blocked from  delivery,  it
       is unspecified whether that signal has any effect other than causing usleep() to return.

       If  a  signal-catching  function interrupts usleep() and examines or changes either the time a SIGALRM is
       scheduled to be generated, the action associated with the SIGALRM signal, or whether the  SIGALRM  signal
       is blocked from delivery, the results are unspecified.

       If  a  signal-catching  function  interrupts  usleep()  and calls siglongjmp() or longjmp() to restore an
       environment saved prior to the usleep() call, the action associated with the SIGALRM signal and the  time
       at  which  a  SIGALRM signal is scheduled to be generated are unspecified. It is also unspecified whether
       the SIGALRM signal is blocked, unless the process' signal mask is restored as part of the environment.

       Implementations may place limitations on the granularity of timer values. For each interval timer, if the
       requested timer value requires a finer granularity than the implementation  supports,  the  actual  timer
       value shall be rounded up to the next supported value.

       Interactions between usleep() and any of the following are unspecified:

              nanosleep()
              setitimer()
              timer_create()
              timer_delete()
              timer_getoverrun()
              timer_gettime()
              timer_settime()
              ualarm()
              sleep()

RETURN VALUE

       Upon  successful  completion,  usleep()  shall  return  0; otherwise, it shall return -1 and set errno to
       indicate the error.

ERRORS

       The usleep() function may fail if:

       EINVAL The time interval specified one million or more microseconds.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications are recommended to use nanosleep() if  the  Timers  option  is  supported,  or  setitimer(),
       timer_create(),  timer_delete(),  timer_getoverrun(), timer_gettime(), or timer_settime() instead of this
       function.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       alarm() , getitimer() ,  nanosleep()  ,  sigaction()  ,  sleep()  ,  timer_create()  ,  timer_delete()  ,
       timer_getoverrun() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                             USLEEP(P)