nanosleep - pause execution for a specified time
int nanosleep(const struct timespec *req, struct timespec
nanosleep delays the execution of the program for at least
the time specified in *req. The function can return ear
lier if a signal has been delivered to the process. In
this case, it returns -1, sets errno to EINTR, and writes
the remaining time into the structure pointed to by rem
unless rem is NULL. The value of *rem can then be used to
call nanosleep again and complete the specified pause.
The structure timespec is used to specify intervals of
time with nanosecond precision. It is specified in
<time.h> and has the form
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
The value of the nanoseconds field must be in the range 0
to 999 999 999.
Compared to sleep(3) and usleep(3), nanosleep has the
advantage of not affecting any signals, it is standardized
by POSIX, it provides higher timing resolution, and it
allows to continue a sleep that has been interrupted by a
signal more easily.
In case of an error or exception, the nanosleep system
call returns -1 instead of 0 and sets errno to one of the
EINTR The pause has been interrupted by a non-blocked
signal that was delivered to the process. The
remaining sleep time has been written into *rem so
that the process can easily call nanosleep again
and continue with the pause.
EINVAL The value in the tv_nsec field was not in the range
0 to 999 999 999 or tv_sec was negative.
The current implementation of nanosleep is based on the
Therefore, nanosleep pauses always for at least the speci
fied time, however it can take up to 10 ms longer than
specified until the process becomes runnable again. For
the same reason, the value returned in case of a delivered
signal in *rem is usually rounded to the next larger mul
tiple of 1/HZ s.
As some applications require much more precise pauses
(e.g., in order to control some time-critical hardware),
nanosleep is also capable of short high-precision pauses.
If the process is scheduled under a real-time policy like
SCHED_FIFO or SCHED_RR, then pauses of up to 2 ms will be
performed as busy waits with microsecond precision.
POSIX.1b (formerly POSIX.4).
sleep(3), usleep(3), sched_setscheduler(2), timer_cre