Provided by: manpages-dev_2.17-1_all
nanosleep - pause execution for a specified time
#define _POSIX_C_SOURCE 199309 #include <time.h>
int nanosleep(const struct timespec *req, struct timespec *rem);
nanosleep() delays the execution of the program for at least the time
specified in *req. The function can return earlier 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 999999999.
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 following values:
EFAULT Problem with copying information from user space.
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
999999999 or tv_sec was negative.
The current implementation of nanosleep() is based on the normal kernel
timer mechanism, which has a resolution of 1/HZ s (i.e, 10 ms on
Linux/i386 and 1 ms on Linux/Alpha). Therefore, nanosleep() pauses
always for at least the specified 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 multiple of 1/HZ s.
In order to support applications requiring much more precise pauses
(e.g., in order to control some time-critical hardware), nanosleep()
would handle pauses of up to 2 ms by busy waiting with microsecond
precision when called from a process scheduled under a real-time policy
like SCHED_FIFO or SCHED_RR. This special extension was removed in
kernel 2.5.39, hence is still present in current 2.4 kernels, but not
in 2.6 kernels.
POSIX.1b (formerly POSIX.4).
sched_setscheduler(2), timer_create(2), sleep(3), usleep(3)