#include <unistd.h>

       int usleep(useconds_t usec);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           Since glibc 2.12:
               _BSD_SOURCE ||
                   (_XOPEN_SOURCE >= 500 ||
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
                   !(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||

       The usleep() function suspends execution of the calling thread for  (at
       least)  usec microseconds.  The sleep may be lengthened slightly by any
       system activity or by the time spent processing  the  call  or  by  the
       granularity of system timers.

       The  usleep() function returns 0 on success.  On error, -1 is returned,
       with errno set to indicate the cause of the error.

       EINTR  Interrupted by a signal; see signal(7).

       EINVAL usec is not smaller than 1000000.  (On  systems  where  that  is
              considered an error.)

       4.3BSD,  POSIX.1-2001.   POSIX.1-2001  declares this function obsolete;
       use nanosleep(2) instead.  POSIX.1-2008 removes  the  specification  of

       On  the original BSD implementation, and in glibc before version 2.2.2,
       the return type of this function is void.  The  POSIX  version  returns
       int, and this is also the prototype used since glibc 2.2.2.

       Only the EINVAL error return is documented by SUSv2 and POSIX.1-2001.

       The  type  useconds_t  is  an  unsigned integer type capable of holding
       integers in the range [0,1000000].  Programs will be more  portable  if
       they never mention this type explicitly.  Use

           #include <unistd.h>
               unsigned int usecs;

       This  page  is  part of release 3.54 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

                                  2013-04-19                         USLEEP(3)
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