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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
NANOSLEEP(2) Linux Programmer's Manual NANOSLEEP(2)
nanosleep - high-resolution sleep
#include <time.h>
int nanosleep(const struct timespec *req, struct timespec *rem);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nanosleep(): _POSIX_C_SOURCE >= 199309L
nanosleep() suspends the execution of the calling thread until either
at least the time specified in *req has elapsed, or the delivery of a
signal that triggers the invocation of a handler in the calling
thread or that terminates the process.
If the call is interrupted by a signal handler, nanosleep() returns
-1, sets errno to EINTR, and writes the remaining time into the
structure pointed to by rem unless rem is NULL. The value of *rem
can then be used to call nanosleep() again and complete the specified
pause (but see NOTES).
The structure timespec is used to specify intervals of time with
nanosecond precision. It is defined as follows:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
The value of the nanoseconds field must be in the range 0 to
999999999.
Compared to sleep(3) and usleep(3), nanosleep() has the following
advantages: it provides a higher resolution for specifying the sleep
interval; POSIX.1 explicitly specifies that it does not interact with
signals; and it makes the task of resuming a sleep that has been
interrupted by a signal handler easier.
On successfully sleeping for the requested interval, nanosleep()
returns 0. If the call is interrupted by a signal handler or
encounters an error, then it returns -1, with errno set to indicate
the error.
EFAULT Problem with copying information from user space.
EINTR The pause has been interrupted by a signal that was delivered
to the thread (see signal(7)). The remaining sleep time has
been written into *rem so that the thread can easily call
nanosleep() again and continue with the pause.
EINVAL The value in the tv_nsec field was not in the range 0 to
999999999 or tv_sec was negative.
POSIX.1-2001, POSIX.1-2008.
If the interval specified in req is not an exact multiple of the
granularity underlying clock (see time(7)), then the interval will be
rounded up to the next multiple. Furthermore, after the sleep
completes, there may still be a delay before the CPU becomes free to
once again execute the calling thread.
The fact that nanosleep() sleeps for a relative interval can be
problematic if the call is repeatedly restarted after being
interrupted by signals, since the time between the interruptions and
restarts of the call will lead to drift in the time when the sleep
finally completes. This problem can be avoided by using
clock_nanosleep(2) with an absolute time value.
POSIX.1 specifies that nanosleep() should measure time against the
CLOCK_REALTIME clock. However, Linux measures the time using the
CLOCK_MONOTONIC clock. This probably does not matter, since the
POSIX.1 specification for clock_settime(2) says that discontinuous
changes in CLOCK_REALTIME should not affect nanosleep():
Setting the value of the CLOCK_REALTIME clock via
clock_settime(2) shall have no effect on threads that are
blocked waiting for a relative time service based upon this
clock, including the nanosleep() function; ... Consequently,
these time services shall expire when the requested relative
interval elapses, independently of the new or old value of the
clock.
Old behavior
In order to support applications requiring much more precise pauses
(e.g., in order to control some time-critical hardware), nanosleep()
would handle pauses of up to 2 milliseconds by busy waiting with
microsecond precision when called from a thread scheduled under a
real-time policy like SCHED_FIFO or SCHED_RR. This special extension
was removed in kernel 2.5.39, and is thus not available in Linux
2.6.0 and later kernels.
If a program that catches signals and uses nanosleep() receives
signals at a very high rate, then scheduling delays and rounding
errors in the kernel's calculation of the sleep interval and the
returned remain value mean that the remain value may steadily
increase on successive restarts of the nanosleep() call. To avoid
such problems, use clock_nanosleep(2) with the TIMER_ABSTIME flag to
sleep to an absolute deadline.
In Linux 2.4, if nanosleep() is stopped by a signal (e.g., SIGTSTP),
then the call fails with the error EINTR after the thread is resumed
by a SIGCONT signal. If the system call is subsequently restarted,
then the time that the thread spent in the stopped state is not
counted against the sleep interval. This problem is fixed in Linux
2.6.0 and later kernels.
clock_nanosleep(2), restart_syscall(2), sched_setscheduler(2),
timer_create(2), sleep(3), usleep(3), time(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-03-13 NANOSLEEP(2)
Pages that refer to this page: pmsleep(1), clock_nanosleep(2), prctl(2), restart_syscall(2), syscalls(2), aio_suspend(3), getaddrinfo_a(3), sleep(3), ualarm(3), usleep(3), signal(7), time(7)