|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
CLOCK_NANOSLEEP(3P) POSIX Programmer's Manual CLOCK_NANOSLEEP(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
clock_nanosleep — high resolution sleep with specifiable clock
#include <time.h>
int clock_nanosleep(clockid_t clock_id, int flags,
const struct timespec *rqtp, struct timespec *rmtp);
If the flag TIMER_ABSTIME is not set in the flags argument, the
clock_nanosleep() function shall cause the current thread to be
suspended from execution until either the time interval specified by
the rqtp argument has elapsed, or a signal is delivered to the
calling thread and its action is to invoke a signal-catching
function, or the process is terminated. The clock used to measure the
time shall be the clock specified by clock_id.
If the flag TIMER_ABSTIME is set in the flags argument, the
clock_nanosleep() function shall cause the current thread to be
suspended from execution until either the time value of the clock
specified by clock_id reaches the absolute time specified by the rqtp
argument, or a signal is delivered to the calling thread and its
action is to invoke a signal-catching function, or the process is
terminated. If, at the time of the call, the time value specified by
rqtp is less than or equal to the time value of the specified clock,
then clock_nanosleep() shall return immediately and the calling
process shall not be suspended.
The suspension time caused by this function may be longer than
requested because the argument value is rounded up to an integer
multiple of the sleep resolution, or because of the scheduling of
other activity by the system. But, except for the case of being
interrupted by a signal, the suspension time for the relative
clock_nanosleep() function (that is, with the TIMER_ABSTIME flag not
set) shall not be less than the time interval specified by rqtp, as
measured by the corresponding clock. The suspension for the absolute
clock_nanosleep() function (that is, with the TIMER_ABSTIME flag set)
shall be in effect at least until the value of the corresponding
clock reaches the absolute time specified by rqtp, except for the
case of being interrupted by a signal.
The use of the clock_nanosleep() function shall have no effect on the
action or blockage of any signal.
The clock_nanosleep() function shall fail if the clock_id argument
refers to the CPU-time clock of the calling thread. It is unspecified
whether clock_id values of other CPU-time clocks are allowed.
If the clock_nanosleep() function returns because the requested time
has elapsed, its return value shall be zero.
If the clock_nanosleep() function returns because it has been
interrupted by a signal, it shall return the corresponding error
value. For the relative clock_nanosleep() function, if the rmtp
argument is non-NULL, the timespec structure referenced by it shall
be updated to contain the amount of time remaining in the interval
(the requested time minus the time actually slept). If the rmtp
argument is NULL, the remaining time is not returned. The absolute
clock_nanosleep() function has no effect on the structure referenced
by rmtp.
If clock_nanosleep() fails, it shall return the corresponding error
value.
The clock_nanosleep() function shall fail if:
EINTR The clock_nanosleep() function was interrupted by a signal.
EINVAL The rqtp argument specified a nanosecond value less than zero
or greater than or equal to 1000 million; or the TIMER_ABSTIME
flag was specified in flags and the rqtp argument is outside
the range for the clock specified by clock_id; or the clock_id
argument does not specify a known clock, or specifies the CPU-
time clock of the calling thread.
ENOTSUP
The clock_id argument specifies a clock for which
clock_nanosleep() is not supported, such as a CPU-time clock.
The following sections are informative.
None.
Calling clock_nanosleep() with the value TIMER_ABSTIME not set in the
flags argument and with a clock_id of CLOCK_REALTIME is equivalent to
calling nanosleep() with the same rqtp and rmtp arguments.
The nanosleep() function specifies that the system-wide clock
CLOCK_REALTIME is used to measure the elapsed time for this time
service. However, with the introduction of the monotonic clock
CLOCK_MONOTONIC a new relative sleep function is needed to allow an
application to take advantage of the special characteristics of this
clock.
There are many applications in which a process needs to be suspended
and then activated multiple times in a periodic way; for example, to
poll the status of a non-interrupting device or to refresh a display
device. For these cases, it is known that precise periodic activation
cannot be achieved with a relative sleep() or nanosleep() function
call. Suppose, for example, a periodic process that is activated at
time T0, executes for a while, and then wants to suspend itself until
time T0+T, the period being T. If this process wants to use the
nanosleep() function, it must first call clock_gettime() to get the
current time, then calculate the difference between the current time
and T0+T and, finally, call nanosleep() using the computed interval.
However, the process could be preempted by a different process
between the two function calls, and in this case the interval
computed would be wrong; the process would wake up later than
desired. This problem would not occur with the absolute
clock_nanosleep() function, since only one function call would be
necessary to suspend the process until the desired time. In other
cases, however, a relative sleep is needed, and that is why both
functionalities are required.
Although it is possible to implement periodic processes using the
timers interface, this implementation would require the use of
signals, and the reservation of some signal numbers. In this regard,
the reasons for including an absolute version of the
clock_nanosleep() function in POSIX.1‐2008 are the same as for the
inclusion of the relative nanosleep().
It is also possible to implement precise periodic processes using
pthread_cond_timedwait(), in which an absolute timeout is specified
that takes effect if the condition variable involved is never
signaled. However, the use of this interface is unnatural, and
involves performing other operations on mutexes and condition
variables that imply an unnecessary overhead. Furthermore,
pthread_cond_timedwait() is not available in implementations that do
not support threads.
Although the interface of the relative and absolute versions of the
new high resolution sleep service is the same clock_nanosleep()
function, the rmtp argument is only used in the relative sleep. This
argument is needed in the relative clock_nanosleep() function to
reissue the function call if it is interrupted by a signal, but it is
not needed in the absolute clock_nanosleep() function call; if the
call is interrupted by a signal, the absolute clock_nanosleep()
function can be invoked again with the same rqtp argument used in the
interrupted call.
None.
clock_getres(3p), nanosleep(3p), pthread_cond_timedwait(3p),
sleep(3p)
The Base Definitions volume of POSIX.1‐2008, time.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 CLOCK_NANOSLEEP(3P)
Pages that refer to this page: time.h(0p), clock_getres(3p), nanosleep(3p)