-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" Copyright (C) Markus Kuhn, 1996
.\" and Copyright (C) Linux Foundation, 2008, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
-.\" License along with this manual; if not, write to the Free
-.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
-.\" USA.
+.\" License along with this manual; if not, see
+.\" <http://www.gnu.org/licenses/>.
+.\" %%%LICENSE_END
.\"
.\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
.\" First version written
.\" NOTES: describe case where clock_nanosleep() can be preferable.
.\" NOTES: describe CLOCK_REALTIME versus CLOCK_NANOSLEEP
.\" Replace crufty discussion of HZ with a pointer to time(7).
-.TH NANOSLEEP 2 2009-01-19 "Linux" "Linux Programmer's Manual"
+.TH NANOSLEEP 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
nanosleep \- high-resolution sleep
.SH SYNOPSIS
.B #include <time.h>
-.sp
+.PP
.BI "int nanosleep(const struct timespec *" req ", struct timespec *" rem );
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.PP
.BR nanosleep ():
_POSIX_C_SOURCE\ >=\ 199309L
.SH DESCRIPTION
has elapsed, or the delivery of a signal
that triggers the invocation of a handler in the calling thread or
that terminates the process.
-
+.PP
If the call is interrupted by a signal handler,
.BR nanosleep ()
-returns \-1, sets \fIerrno\fP to
+returns \-1, sets
+.I errno
+to
.BR EINTR ,
and writes the remaining time into the structure pointed to by
.I rem
can then be used to call
.BR nanosleep ()
again and complete the specified pause (but see NOTES).
-
+.PP
The structure
.I timespec
is used to specify intervals of time with nanosecond precision.
It is defined as follows:
-.sp
+.PP
.in +4n
-.nf
+.EX
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
-.fi
+.EE
.in
.PP
The value of the nanoseconds field must be in the range 0 to 999999999.
-
+.PP
Compared to
-.BR sleep (3)
+.BR sleep (3)
and
.BR usleep (3),
.BR nanosleep ()
.TP
.B EINTR
The pause has been interrupted by a signal that was
-delivered to the thread.
+delivered to the thread (see
+.BR signal (7)).
The remaining sleep time has been written
-into \fI*rem\fP so that the thread can easily call
+into
+.I *rem
+so that the thread can easily call
.BR nanosleep ()
again and continue with the pause.
.TP
.I tv_sec
was negative.
.SH CONFORMING TO
-POSIX.1-2001.
+POSIX.1-2001, POSIX.1-2008.
.SH NOTES
If the interval specified in
.I req
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.
-
+.PP
The fact that
.BR nanosleep ()
sleeps for a relative interval can be problematic if the call
This problem can be avoided by using
.BR clock_nanosleep (2)
with an absolute time value.
-
+.PP
POSIX.1 specifies that
.BR nanosleep ()
should measure time against the
Consequently, these time services shall expire when the requested relative
interval elapses, independently of the new or old value of the clock.
.RE
-.SS "Old behavior"
+.SS Old behavior
In order to support applications requiring much more precise pauses
(e.g., in order to control some time-critical hardware),
.BR nanosleep ()
-would handle pauses of up to 2\ ms by busy waiting with microsecond
+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
.B SCHED_FIFO
or
.BR 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.
+and is thus not available in Linux 2.6.0 and later kernels.
.SH BUGS
+If a program that catches signals and uses
+.BR 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
+.IR remain
+value mean that the
+.IR remain
+value may steadily
+.IR increase
+on successive restarts of the
+.BR nanosleep ()
+call.
+To avoid such problems, use
+.BR clock_nanosleep (2)
+with the
+.BR TIMER_ABSTIME
+flag to sleep to an absolute deadline.
+.PP
In Linux 2.4, if
.BR nanosleep ()
is stopped by a signal (e.g.,
signal.
If the system call is subsequently restarted,
then the time that the thread spent in the stopped state is
-\fInot\fP counted against the sleep interval.
+.I not
+counted against the sleep interval.
+This problem is fixed in Linux 2.6.0 and later kernels.
.SH SEE ALSO
.BR clock_nanosleep (2),
+.BR restart_syscall (2),
.BR sched_setscheduler (2),
.BR timer_create (2),
.BR sleep (3),