nanosleep() - Unix, Linux System Call
Advertisements
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
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
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
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.
RETURN VALUE
On successfully sleeping for the requested interval,
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
Tag | Description |
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.
|
BUGS
The current implementation of
nanosleep() is based on the normal kernel timer mechanism, which has a resolution
of 1/HZ s (see
time(7)).
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.
Old behaviour
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.
In Linux 2.4, if
nanosleep() is stopped by a signal (e.g., SIGTSTP),
then the call fails with the error
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.
CONFORMING TO
POSIX.1-2001.
SEE ALSO
Advertisements
|
To Continue Learning Please Login
Login with Google