NANOSLEEP(P) POSIX Programmer's Manual NANOSLEEP(P)NAMEnanosleep - high resolution sleep (REALTIME)
SYNOPSIS
#include <time.h>
int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);
DESCRIPTION
The 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 to terminate
the process. The suspension time 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 sys‐
tem. But, except for the case of being interrupted by a signal, the
suspension time shall not be less than the time specified by rqtp, as
measured by the system clock CLOCK_REALTIME.
The use of the nanosleep() function has no effect on the action or
blockage of any signal.
RETURN VALUE
If the nanosleep() function returns because the requested time has
elapsed, its return value shall be zero.
If the nanosleep() function returns because it has been interrupted by
a signal, it shall return a value of -1 and set errno to indicate the
interruption. If the rmtp argument is non-NULL, the timespec structure
referenced by it is 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.
If nanosleep() fails, it shall return a value of -1 and set errno to
indicate the error.
ERRORS
The nanosleep() function shall fail if:
EINTR The 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.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
It is common to suspend execution of a process for an interval in order
to poll the status of a non-interrupting function. A large number of
actual needs can be met with a simple extension to sleep() that pro‐
vides finer resolution.
In the POSIX.1-1990 standard and SVR4, it is possible to implement such
a routine, but the frequency of wakeup is limited by the resolution of
the alarm() and sleep() functions. In 4.3 BSD, it is possible to write
such a routine using no static storage and reserving no system facili‐
ties. Although it is possible to write a function with similar func‐
tionality to sleep() using the remainder of the timer_*() functions,
such a function requires the use of signals and the reservation of some
signal number. This volume of IEEE Std 1003.1-2001 requires that
nanosleep() be non-intrusive of the signals function.
The nanosleep() function shall return a value of 0 on success and -1 on
failure or if interrupted. This latter case is different from sleep().
This was done because the remaining time is returned via an argument
structure pointer, rmtp, instead of as the return value.
FUTURE DIRECTIONS
None.
SEE ALSOsleep() , the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 NANOSLEEP(P)
