.\" 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 2016-03-15 "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
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)
and
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
This special extension was removed in kernel 2.5.39,
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.,
then the time that the thread spent in the stopped state is
.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),