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[thirdparty/man-pages.git] / man2 / clock_nanosleep.2

.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
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.TH CLOCK_NANOSLEEP 2 2012-11-07 "Linux" "Linux Programmer's Manual"
.SH NAME
clock_nanosleep \- high-resolution sleep with specifiable clock
.SH SYNOPSIS
.B #include <time.h>
.nf
.sp
.BI "int clock_nanosleep(clockid_t " clock_id ", int " flags ,
.BI "                    const struct timespec *" request ,
.BI "                    struct timespec *" remain );
.fi
.sp
Link with \fI\-lrt\fP (only for glibc versions before 2.17).
.sp
.ad l
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR clock_nanosleep ():
.RS 4
_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
.RE
.ad
.SH DESCRIPTION
Like
.BR nanosleep (2),
.BR clock_nanosleep ()
allows the calling thread to sleep for an interval specified
with nanosecond precision.
It differs in allowing the caller to select the clock against
which the sleep interval is to be measured,
and in allowing the sleep interval to be specified as
either an absolute or a relative value.

The time values passed to and returned by this call are specified using
.I timespec
structures, defined as follows:
.sp
.in +4n
.nf
struct timespec {
    time_t tv_sec;        /* seconds */
    long   tv_nsec;       /* nanoseconds [0 .. 999999999] */
};
.fi
.in

The
.I clock_id
argument specifies the clock against which the sleep interval
is to be measured.
This argument can have one of the following values:
.TP 17
.BR CLOCK_REALTIME
A settable system-wide real-time clock.
.TP
.BR CLOCK_MONOTONIC
A nonsettable, monotonically increasing clock that measures time
since some unspecified point in the past that does not change after
system startup.
.\" On Linux this clock measures time since boot.
.TP
.BR CLOCK_PROCESS_CPUTIME_ID
A settable per-process clock that measures CPU time consumed
by all threads in the process.
.\" There is some trickery between glibc and the kernel
.\" to deal with the CLOCK_PROCESS_CPUTIME_ID case.
.PP
See
.BR clock_getres (2)
for further details on these clocks.

If
.I flags
is 0, then the value specified in
.I request
is interpreted as an interval relative to the current
value of the clock specified by
.IR clock_id .

If
.I flags
is
.BR TIMER_ABSTIME ,
then
.I request
is interpreted as an absolute time as measured by the clock,
.IR clock_id .
If
.I request
is less than or equal to the current value of the clock,
then
.BR clock_nanosleep ()
returns immediately without suspending the calling thread.

.BR clock_nanosleep ()
suspends the execution of the calling thread
until either at least the time specified by
.IR request
has elapsed,
or a signal is delivered that causes a signal handler to be called or
that terminates the process.

If the call is interrupted by a signal handler,
.BR clock_nanosleep ()
fails with the error
.BR EINTR .
In addition, if
.I remain
is not NULL, and
.I flags
was not
.BR TIMER_ABSTIME ,
it returns the remaining unslept time in
.IR remain .
This value can then be used to call
.BR clock_nanosleep ()
again and complete a (relative) sleep.
.SH RETURN VALUE
On successfully sleeping for the requested interval,
.BR clock_nanosleep ()
returns 0.
If the call is interrupted by a signal handler or encounters an error,
then it returns one of the positive error number listed in ERRORS.
.SH ERRORS