clock_nanosleep()

High resolution sleep with specifiable clock

Synopsis:

#include <time.h>

int clock_nanosleep( clockid_t clock_id,
                     int flags,
                     const struct timespec * rqtp,
                     struct timespec * rmtp );

Library:

libc

Description:

The clock_nanosleep() function suspends the current thread from execution until:

• If TIMER_ABSTIME is set, the time value of the clock specified by clock_id reaches the absolute time specified by the rqtp argument.

  Or:

• If TIMER_ABSTIME is not set, the time interval specified by the rqtp argument has elapsed.

  Or:

• A signal is delivered to the calling thread, and the signal's action is to invoke a signal-catching function or terminate the process.

where:

clock_id

Specifies the clock that's used to measure the time. The possible clock types are:

CLOCK_MONOTONIC

A clock that always increases at a constant rate and can't be adjusted.

CLOCK_SOFTTIME

Same as CLOCK_REALTIME, but if the CPU is in powerdown mode, the clock stops running.

CLOCK_REALTIME

A clock that maintains the system time.

flags

Specifies when the current thread is to be suspended from execution:

• when the time interval specified by the rqtp argument has elapsed (TIMER_ABSTIME is not set).
• when the time value of the clock specified by clock_id reaches the absolute time specified by the rqtp argument (TIMER_ABSTIME is set). 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() returns immediately and the calling process isn't suspended.
• when a signal is delivered to the calling thread and the signal's action is to invoke a signal-catching function or terminate the process.

Calling clock_nanosleep() with TIMER_ABSTIME not set and clock_id set to CLOCK_REALTIME is the equivalent to calling nanosleep() with the same rqtp and rmtp arguments.

rqtp

Specifies the time interval between the requested time and the time actually slept.

rmtp

The amount of time remaining in an interval.

For the relative clock_nanosleep() function, if rmtp isn't 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 it's NULL, the remaining time isn't returned. The absolute clock_nanosleep() function has no effect on the structure referenced by rmtp.

The nanosleep() function always uses CLOCK_REALTIME.

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 scheduling and other system activity. Except for the case of being interrupted by a signal, the suspension time for:

• the relative clock_nanosleep() function (TIMER_ABSTIME not set) -- isn't less than the time interval specified by rqtp, as measured by the corresponding clock
• the absolute clock_nanosleep() function (TIMER_ABSTIME set) -- is 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 has no effect on the action or blockage of any signal.

The clock_nanosleep() function fails if the clock_id argument refers to the CPU-time clock of the calling thread. It's unspecified if clock_id values of other CPU-time clocks are allowed.

Returns:

Zero if the requested time has elapsed, or a corresponding error value if clock_nanosleep() has been interrupted by a signal, or fails.

Errors:

EINTR

The call 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 TIMER_ABSTIME is specified in flags and the rqtp argument is outside the range for the clock specified by clock_id; or the clock_id argument doesn't 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() isn't supported, such as a CPU-time clock.

Classification:

POSIX 1003.1j (draft)

See also:

clock_settime(), nanosleep(), sleep()