NANOSLEEP(2)

NAME
nanosleep - high resolution sleep

LIBRARY
libc

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. 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_TAI
CLOCK_UPTIME
CLOCK_UPTIME_FAST
CLOCK_UPTIME_PRECISE

The suspension time may be longer than requested due to the scheduling of other activity by the system. The clocks with the _FAST suffix and the CLOCK_SECOND are subject to the allowed time interval deviation specified by the kern.timecounter.alloweddeviation sysctl(8) variable. The clocks with the _PRECISE suffix are always as precise as possible. The CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_UPTIME are precise by default. Setting the kern.timecounter.nanosleep_precise sysctl(8) to a false value would make those clocks to behave like the _FAST clocks.

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 p1003.1-2008.

HISTORY
The predecessor of this system call, sleep(), appeared in AT&T UNIX, but was removed when alarm(3) was introduced into AT&T UNIX. The nanosleep() system call has been available since NetBSD 1.3 and was ported to OpenBSD 2.1 and FreeBSD 3.0. The clock_nanosleep() system call has been available since FreeBSD 11.1.

In FreeBSD 15.0 the default behavior of clock_nanosleep() with CLOCK_MONOTONIC, CLOCK_REALTIME, CLOCK_UPTIME clocks and nanosleep() has been switched to use precise clock.