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Manuál Linux
[Linux manuál]

nanosleep: pozastavit provádění po stanovenou dobu

Originální popis anglicky: nanosleep - pause execution for a specified time

Návod, kniha: Linux Programmer's Manual

STRUČNĚ

#include <time.h>
 
int nanosleep(const struct timespec *req, struct timespec *rem);

POPIS / INSTRUKCE

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.

CHYBY / ERRORY

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.

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.
 

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.

ODPOVÍDAJÍCÍ

POSIX.1b (formerly POSIX.4).

SOUVISEJÍCÍ

sched_setscheduler(2), timer_create(2), sleep(3), usleep(3)
2004-10-24 Linux 2.6.9
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