NANOSLEEP (2)
pause execution for a specified time
SYNOPSIS
#include <time.h>
int nanosleep(const struct timespec *req, struct timespec *rem);
DESCRIPTION
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
12
8n 16n 32n
struct timespec
{
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.
ERRORS
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:
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.
BUGS
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.
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.
CONFORMING TO
POSIX.1b (formerly POSIX.4).
SEE ALSO
sleep(3) - usleep (3) -
sched_setscheduler(2) timer_create(2)
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