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NANOSLEEP(2) System Calls Manual NANOSLEEP(2) NAME nanosleep -- high resolution sleep LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <time.h> int clock_nanosleep(clockid_t clock_id, int flags, const struct timespec *rqtp, struct timespec *rmtp); int nanosleep(const struct timespec *rqtp, struct timespec *rmtp); DESCRIPTION If the TIMER_ABSTIME flag is not set in the flags argument, then clock_nanosleep() suspends execution of the calling thread until either the time interval specified by the rqtp argument has elapsed, or a signal is delivered to the calling process and its action is to invoke a signal- catching function or to terminate the process. The clock used to measure the time is specified by the clock_id argument. If the TIMER_ABSTIME flag is set in the flags argument, then clock_nanosleep() suspends execution of the calling thread until either the value of the clock specified by the clock_id argument reaches the absolute time specified by the rqtp argument, or a signal is delivered to the call- ing process and its action is to invoke a signal-catching function or to terminate the process. If, at the time of the call, the time value speci- fied by rqtp is less than or equal to the time value of the specified clock, then clock_nanosleep() returns immediately and the calling thread is not suspended. An unmasked signal will terminate the sleep early, regard- less of the SA_RESTART value on the interrupting signal. The rqtp and rmtp arguments can point to the same object. The following clock_id values are supported: CLOCK_MONOTONIC CLOCK_MONOTONIC_FAST CLOCK_MONOTONIC_PRECISE CLOCK_REALTIME CLOCK_REALTIME_FAST CLOCK_REALTIME_PRECISE CLOCK_SECOND CLOCK_TAI CLOCK_UPTIME CLOCK_UPTIME_FAST CLOCK_UPTIME_PRECISE The suspension time may be longer than requested due to the scheduling of other activity by the system. The clocks with the _FAST suffix and the CLOCK_SECOND are subject to the allowed time interval deviation specified by the kern.timecounter.alloweddeviation sysctl(8) variable. The clocks with the _PRECISE suffix are always as precise as possible. The CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_UPTIME are precise by default. Setting the kern.timecounter.nanosleep_precise sysctl(8) to a false value would make those clocks to behave like the _FAST clocks. The nanosleep() function behaves like clock_nanosleep() with a clock_id ar- gument of CLOCK_REALTIME and without the TIMER_ABSTIME flag in the flags argument. RETURN VALUES These functions return zero when the requested time has elapsed. If these functions return for any other reason, then clock_nanosleep() will directly return the error number, and nanosleep() will return -1 with the global variable errno set to indicate the error. If a relative sleep is interrupted by a signal and rmtp is non-NULL, the timespec structure it references is updated to contain the unslept amount (the request time minus the time actually slept). ERRORS These functions can fail with the following errors. [EFAULT] Either rqtp or rmtp points to memory that is not a valid part of the process address space. [EINTR] The function was interrupted by the delivery of a sig- nal. [EINVAL] The rqtp argument specified a nanosecond value less than zero or greater than or equal to 1000 million. [EINVAL] The flags argument contained an invalid flag. [EINVAL] The clock_id argument was CLOCK_THREAD_CPUTIME_ID or an unrecognized value. [ENOTSUP] The clock_id argument was valid but not supported by this implementation of clock_nanosleep(). SEE ALSO clock_gettime(2), sigaction(2), sleep(3) STANDARDS These functions conform to IEEE Std 1003.1-2008 ("POSIX.1"). HISTORY The predecessor of this system call, sleep(), appeared in Version 3 AT&T UNIX, but was removed when alarm(3) was introduced into Version 7 AT&T UNIX. The nanosleep() system call has been available since NetBSD 1.3 and was ported to OpenBSD 2.1 and FreeBSD 3.0. The clock_nanosleep() system call has been available since FreeBSD 11.1. In FreeBSD 15.0 the default behavior of clock_nanosleep() with CLOCK_MONOTONIC, CLOCK_REALTIME, CLOCK_UPTIME clocks and nanosleep() has been switched to use precise clock. FreeBSD ports 15.quarterly May 3, 2025 NANOSLEEP(2)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY
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