| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON | The Linux Programming Interface |
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. 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.
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.
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 ms 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, hence is still present in
current 2.4 kernels, but not in 2.6 kernels.
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.
clock_nanosleep(2), sched_setscheduler(2), timer_create(2), sleep(3),
usleep(3), time(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2009-01-19 NANOSLEEP(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface