Man

Command Section
NANOSLEEP(2)              FreeBSD System Calls Manual             NANOSLEEP(2)

NAME
     nanosleep - high resolution sleep

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <time.h>

     int
     clock_nanosleep(clockid_t clock_id, int flags,
         const struct timespec *rqtp, struct timespec *rmtp);

     int
     nanosleep(const struct timespec *rqtp, struct timespec *rmtp);

DESCRIPTION
     If the TIMER_ABSTIME flag is not set in the flags argument, then
     clock_nanosleep() suspends execution of the calling thread until either
     the time interval specified by the rqtp argument has elapsed, or a signal
     is delivered to the calling process and its action is to invoke a signal-
     catching function or to terminate the process.  The clock used to measure
     the time is specified by the clock_id argument.

     If the TIMER_ABSTIME flag is set in the flags argument, then
     clock_nanosleep() suspends execution of the calling thread until either
     the value of the clock specified by the clock_id argument reaches the
     absolute time specified by the rqtp argument, or a signal is delivered to
     the calling process and its action is to invoke a signal-catching
     function or to terminate the process.  If, at the time of the call, the
     time value specified by rqtp is less than or equal to the time value of
     the specified clock, then clock_nanosleep() returns immediately and the
     calling thread is not suspended.

     The suspension time may be longer than requested due to the scheduling of
     other activity by the system.  An unmasked signal will terminate the
     sleep early, regardless of the SA_RESTART value on the interrupting
     signal.  The rqtp and rmtp arguments can point to the same object.

     The following clock_id values are supported:

           CLOCK_MONOTONIC
           CLOCK_MONOTONIC_FAST
           CLOCK_MONOTONIC_PRECISE
           CLOCK_REALTIME
           CLOCK_REALTIME_FAST
           CLOCK_REALTIME_PRECISE
           CLOCK_SECOND
           CLOCK_UPTIME
           CLOCK_UPTIME_FAST
           CLOCK_UPTIME_PRECISE

     The nanosleep() function behaves like clock_nanosleep() with a clock_id
     argument of CLOCK_REALTIME and without the TIMER_ABSTIME flag in the
     flags argument.

RETURN VALUES
     These functions return zero when the requested time has elapsed.

     If these functions return for any other reason, then clock_nanosleep()
     will directly return the error number, and nanosleep() will return -1
     with the global variable errno set to indicate the error.  If a relative
     sleep is interrupted by a signal and rmtp is non-NULL, the timespec
     structure it references is updated to contain the unslept amount (the
     request time minus the time actually slept).

ERRORS
     These functions can fail with the following errors.

     [EFAULT]           Either rqtp or rmtp points to memory that is not a
                        valid part of the process address space.

     [EINTR]            The function was interrupted by the delivery of a
                        signal.

     [EINVAL]           The rqtp argument specified a nanosecond value less
                        than zero or greater than or equal to 1000 million.

     [EINVAL]           The flags argument contained an invalid flag.

     [EINVAL]           The clock_id argument was CLOCK_THREAD_CPUTIME_ID or
                        an unrecognized value.

     [ENOTSUP]          The clock_id argument was valid but not supported by
                        this implementation of clock_nanosleep().

SEE ALSO
     clock_gettime(2), sigaction(2), sleep(3)

STANDARDS
     These functions conform to IEEE Std 1003.1-2008 (``POSIX.1'').

FreeBSD 11.1-RELEASE-p4         March 17, 2017         FreeBSD 11.1-RELEASE-p4
Command Section