NAME
nanosleep - pause execution for a specified time
SYNOPSIS
#define _POSIX_C_SOURCE 199309
#include <time.h>
int nanosleep(const struct timespec *req, struct timespec *rem);
DESCRIPTION
R nanosleep ()
delays the execution of the program for at least the time specified in
R *req .
The function can return earlier if a signal has been delivered to the
process.
In this case, it returns -1, sets
errno to
R EINTR ,
and writes the
remaining time into the structure pointed to by
R rem
unless
rem
is NULL.
The value of
*rem
can then be used to call
R 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
struct timespec {
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
R sleep (3)
and
usleep(3),
R 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.
RETURN VALUE
On successfully sleeping for the requested interval,
R nanosleep ()
returns 0.
If the call is interrupted by a signal handler or encounters an error,
then it returns -1, with
errno
set to indicate the error.
ERRORS
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
R 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.
CONFORMING TO
POSIX.1-2001.
BUGS
The current implementation of
R nanosleep ()
is based on the normal kernel timer mechanism, which has a resolution
of 1/
HZ s (see
time(7)).
Therefore,
R 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.
Old behavior
In order to support applications requiring much more precise pauses
(e.g., in order to control some time-critical hardware),
R 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
R 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.
In Linux 2.4, if
R nanosleep ()
is stopped by a signal (e.g.,
R SIGTSTP ),
then the call fails with the error
R EINTR
after the process is resumed by a
SIGCONT
signal.
If the system call is subsequently restarted,
then the time that the process spent in the stopped state is
not counted against the sleep interval.
SEE ALSO
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