Originální popis anglicky:
nanosleep - pause execution for a specified time
Návod, kniha: Linux Programmer's Manual
int nanosleep(const struct timespec *req, struct timespec
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
, and writes the remaining time into the structure pointed to by
. The value of *rem
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
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
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:
- Problem with copying information from user space.
- 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.
- 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
10 ms on Linux/i386 and 1 ms on Linux/Alpha). Therefore,
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/
In order to support applications requiring much more precise pauses (e.g., in
order to control some time-critical hardware), nanosleep
pauses of up to 2 ms by busy waiting with microsecond precision when
called from a process scheduled under a real-time policy like
. This special extension was removed in
kernel 2.5.39, hence is still present in current 2.4 kernels, but not in 2.6
POSIX.1b (formerly POSIX.4).