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clock_nanosleep(2) System Calls Manual clock_nanosleep(2)
NAME
clock_nanosleep - high-resolution sleep with specifiable clock
LIBRARY
Standard C library (libc, -lc), since glibc 2.17
Before glibc 2.17, Real-time library (librt, -lrt)
SYNOPSIS
#include <time.h>
int clock_nanosleep(clockid_t clockid, int flags,
const struct timespec *request,
struct timespec *_Nullable remain);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
clock_nanosleep():
_POSIX_C_SOURCE >= 200112L
DESCRIPTION
Like nanosleep(2), clock_nanosleep() allows the calling thread to sleep
for an interval specified with nanosecond precision. It differs in al-
lowing 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
timespec(3) structures.
The clockid argument specifies the clock against which the sleep inter-
val is to be measured. This argument can have one of the following
values:
CLOCK_REALTIME
A settable system-wide real-time clock.
CLOCK_TAI (since Linux 3.10)
A system-wide clock derived from wall-clock time but ignoring
leap seconds.
CLOCK_MONOTONIC
A nonsettable, monotonically increasing clock that measures time
since some unspecified point in the past that does not change
after system startup.
CLOCK_BOOTTIME (since Linux 2.6.39)
Identical to CLOCK_MONOTONIC, except that it also includes any
time that the system is suspended.
CLOCK_PROCESS_CPUTIME_ID
A settable per-process clock that measures CPU time consumed by
all threads in the process.
See clock_getres(2) for further details on these clocks. In addition,
the CPU clock IDs returned by clock_getcpuclockid(3) and
pthread_getcpuclockid(3) can also be passed in clockid.
If flags is 0, then the value specified in request is interpreted as an
interval relative to the current value of the clock specified by
clockid.
If flags is TIMER_ABSTIME, then request is interpreted as an absolute
time as measured by the clock, clockid. If request is less than or
equal to the current value of the clock, then clock_nanosleep() returns
immediately without suspending the calling thread.
clock_nanosleep() suspends the execution of the calling thread until
either at least the time specified by request has elapsed, or a signal
is delivered that causes a signal handler to be called or that termi-
nates the process.
If the call is interrupted by a signal handler, clock_nanosleep() fails
with the error EINTR. In addition, if remain is not NULL, and flags
was not TIMER_ABSTIME, it returns the remaining unslept time in remain.
This value can then be used to call clock_nanosleep() again and com-
plete a (relative) sleep.
RETURN VALUE
On successfully sleeping for the requested interval, clock_nanosleep()
returns 0. If the call is interrupted by a signal handler or encoun-
ters an error, then it returns one of the positive error number listed
in ERRORS.
ERRORS
EFAULT request or remain specified an invalid address.
EINTR The sleep was interrupted by a signal handler; see signal(7).
EINVAL The value in the tv_nsec field was not in the range [0,
999999999] or tv_sec was negative.
EINVAL clockid was invalid. (CLOCK_THREAD_CPUTIME_ID is not a permit-
ted value for clockid.)
ENOTSUP
The kernel does not support sleeping against this clockid.
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001. Linux 2.6, glibc 2.1.
NOTES
If the interval specified in request 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 com-
pletes, there may still be a delay before the CPU becomes free to once
again execute the calling thread.
Using an absolute timer is useful for preventing timer drift problems
of the type described in nanosleep(2). (Such problems are exacerbated
in programs that try to restart a relative sleep that is repeatedly in-
terrupted by signals.) To perform a relative sleep that avoids these
problems, call clock_gettime(2) for the desired clock, add the desired
interval to the returned time value, and then call clock_nanosleep()
with the TIMER_ABSTIME flag.
clock_nanosleep() is never restarted after being interrupted by a sig-
nal handler, regardless of the use of the sigaction(2) SA_RESTART flag.
The remain argument is unused, and unnecessary, when flags is TIMER_AB-
STIME. (An absolute sleep can be restarted using the same request ar-
gument.)
POSIX.1 specifies that clock_nanosleep() has no effect on signals dis-
positions or the signal mask.
POSIX.1 specifies that after changing the value of the CLOCK_REALTIME
clock via clock_settime(2), the new clock value shall be used to deter-
mine the time at which a thread blocked on an absolute
clock_nanosleep() will wake up; if the new clock value falls past the
end of the sleep interval, then the clock_nanosleep() call will return
immediately.
POSIX.1 specifies that changing the value of the CLOCK_REALTIME clock
via clock_settime(2) shall have no effect on a thread that is blocked
on a relative clock_nanosleep().
SEE ALSO
clock_getres(2), nanosleep(2), restart_syscall(2), timer_create(2),
sleep(3), timespec(3), usleep(3), time(7)
Linux man-pages 6.04 2023-03-30 clock_nanosleep(2)
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