NAME
nanosleep — high
resolution sleep (REALTIME)
SYNOPSIS
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 system. 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:
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(3) 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(3) and sleep(3) 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(3) using the remainder
of the timer_create(3) functions, such a function requires
the use of signals and the reservation of some signal number. This volume of
IEEE Std 1003.1-2001 (“POSIX.1”)
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(3). 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 ALSO
sleep(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <time.h>
CHANGE HISTORY
First released in Issue 5. Included for alignment with the POSIX Realtime Extension.
Issue 6
The nanosleep () function is marked as
part of the Timers option.
The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Timers option.
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