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NAME

nanosleep - high-resolution sleep
 

SYNOPSIS

int nanosleep(const struct timespec *req, struct timespec *rem);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

nanosleep(): _POSIX_C_SOURCE >= 199309L  

DESCRIPTION

If the call is interrupted by a signal handler, nanosleep() 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 (but see NOTES).

The structure timespec is used to specify intervals of time with nanosecond precision. It is defined as follows:

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 following advantages: it provides a higher resolution for specifying the sleep interval; POSIX.1 explicitly specifies that it does not interact with signals; and it makes the task of resuming a sleep that has been interrupted by a signal handler easier.  

RETURN VALUE

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 thread. The remaining sleep time has been written into *rem so that the thread 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.

CONFORMING TO

NOTES

The fact that nanosleep() sleeps for a relative interval can be problematic if the call is repeatedly restarted after being interrupted by signals, since the time between the interruptions and restarts of the call will lead to drift in the time when the sleep finally completes. This problem can be avoided by using clock_nanosleep(2) with an absolute time value.

POSIX.1 specifies that nanosleep() should measure time against the CLOCK_REALTIME clock. However, Linux measures the time using the CLOCK_MONOTONIC clock. This probably does not matter, since the POSIX.1 specification for clock_settime() says that discontinuous changes in CLOCK_REALTIME should not affect nanosleep():

Setting the value of the CLOCK_REALTIME clock via clock_settime() shall have no effect on threads that are blocked waiting for a relative time service based upon this clock, including the nanosleep() function; ... Consequently, these time services shall expire when the requested relative interval elapses, independently of the new or old value of the clock.

BUGS

Old behavior

In Linux 2.4, if nanosleep() is stopped by a signal (e.g., SIGTSTP), then the call fails with the error EINTR after the thread is resumed by a SIGCONT signal. If the system call is subsequently restarted, then the time that the thread spent in the stopped state is not counted against the sleep interval.  

SEE ALSO

COLOPHON

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

NOTES

BUGS

Old behavior

SEE ALSO

COLOPHON

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