View Source: nanosleep(2) - Waikato Linux Users Group

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!!NAME
 nanosleep - pause execution for a specified time
!!SYNOPSIS
 __#include <time.h>__
 __int nanosleep(const struct timespec *__''req''__, struct timespec *__''rem''__);__
!!DESCRIPTION
nanosleep(2) 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 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(2) 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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Last edited on Sunday, March 16, 2003 5:50:51 pm by PerryLorier

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