NANOSLEEP(P) POSIX Programmer's Manual NANOSLEEP(P)
nanosleep - high resolution sleep (REALTIME)
int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);
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 system. But, except for the case of being inter-
rupted 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.
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.
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.
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 provides 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 facilities. Although it is possible to write a function with similar functionality
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 remain-
ing time is returned via an argument structure pointer, rmtp, instead of as the return
sleep() , the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 NANOSLEEP(P)