NAME
nanosleep — high
resolution sleep
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). The rqtp and rmtp arguments may
point to the same object. 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 thread 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_*()
functions, such a function requires the use of signals and the reservation
of some signal number. This volume of POSIX.1-2008 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
XBD <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.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 1-2002, item XSH/TC1/D6/37 is applied, updating the SEE ALSO section to include the clock_nanosleep(3) function.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/63 is applied, correcting text in the RATIONALE section.
Issue 7
SD5-XBD-ERN-33 is applied.
The nanosleep () function is moved from
the Timers option to the Base.