.\" Copyright (c) 2005 David Xu .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice(s), this list of conditions and the following disclaimer as .\" the first lines of this file unmodified other than the possible .\" addition of one or more copyright notices. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice(s), this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY .\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE .\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR .\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, .\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE .\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, .\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" $FreeBSD: head/lib/libc/sys/timer_settime.2 235140 2012-05-08 18:56:21Z gjb $ .\" .Dd September 11, 2000 .Dt TIMER_SETTIME 2 .Os .Sh NAME .Nm timer_getoverrun , .Nm timer_gettime , .Nm timer_settime .Nd "per-process timers (REALTIME)" .Sh LIBRARY .Lb librt .Sh SYNOPSIS .In time.h .Ft int .Fn timer_getoverrun "timer_t timerid" .Ft int .Fn timer_gettime "timer_t timerid" "struct itimerspec *value" .Ft int .Fo timer_settime .Fa "timer_t timerid" "int flags" "const struct itimerspec *restrict value" .Fa "struct itimerspec *restrict ovalue" .Fc .Sh DESCRIPTION The .Fn timer_gettime system call stores the amount of time until the specified timer, .Fa timerid , expires and the reload value of the timer into the space pointed to by the .Fa value argument. The .Va it_value member of this structure contains the amount of time before the timer expires, or zero if the timer is disarmed. This value is returned as the interval until timer expiration, even if the timer was armed with absolute time. The .Va it_interval member of .Fa value contains the reload value last set by .Fn timer_settime . .Pp The .Fn timer_settime system call sets the time until the next expiration of the timer specified by .Fa timerid from the .Va it_value member of the .Fa value argument and arms the timer if the .Va it_value member of .Fa value is non-zero. If the specified timer was already armed when .Fn timer_settime is called, this call resets the time until next expiration to the value specified. If the .Va it_value member of .Fa value is zero, the timer is disarmed. If the timer is disarmed, then pending signal is removed. .Pp If the flag .Dv TIMER_ABSTIME is not set in the argument .Fa flags , .Fn timer_settime behaves as if the time until next expiration is set to be equal to the interval specified by the .Va it_value member of .Fa value . That is, the timer expires in .Va it_value nanoseconds from when the call is made. If the flag .Dv TIMER_ABSTIME is set in the argument .Fa flags , .Fn timer_settime behaves as if the time until next expiration is set to be equal to the difference between the absolute time specified by the it_value member of value and the current value of the clock associated with .Fa timerid . That is, the timer expires when the clock reaches the value specified by the .Va it_value member of .Fa value . If the specified time has already passed, the system call succeeds and the expiration notification is made. .Pp The reload value of the timer is set to the value specified by the .Va it_interval member of .Fa value . When a timer is armed with a non-zero .Va it_interval , a periodic (or repetitive) timer is specified. .Pp Time values that are between two consecutive non-negative integer multiples of the resolution of the specified timer are rounded up to the larger multiple of the resolution. Quantization error will not cause the timer to expire earlier than the rounded time value. .Pp If the argument .Fa ovalue is not .Dv NULL , the .Fn timer_settime system call stores, in the location referenced by .Fa ovalue , a value representing the previous amount of time before the timer would have expired, or zero if the timer was disarmed, together with the previous timer reload value. Timers do not expire before their scheduled time. .Pp Only a single signal is queued to the process for a given timer at any point in time. When a timer for which a signal is still pending expires, no signal is queued, and a timer overrun will occur. When a timer expiration signal is accepted by a process, the .Fn timer_getoverrun system call returns the timer expiration overrun count for the specified timer. The overrun count returned contains the number of extra timer expirations that occurred between the time the signal was generated (queued) and when it was accepted, up to but not including an maximum of .Brq Dv DELAYTIMER_MAX . If the number of such extra expirations is greater than or equal to .Brq Dv DELAYTIMER_MAX , then the overrun count is set to .Brq Dv DELAYTIMER_MAX . The value returned by .Fn timer_getoverrun applies to the most recent expiration signal acceptance for the timer. If no expiration signal has been delivered for the timer, the return value of .Fn timer_getoverrun is unspecified. .Sh RETURN VALUES If the .Fn timer_getoverrun system call succeeds, it returns the timer expiration overrun count as explained above. Otherwise the value \-1 is returned, and the global variable .Va errno is set to indicate the error. .Pp .Rv -std timer_gettime timer_settime .Sh ERRORS The .Fn timer_settime system call will fail if: .Bl -tag -width Er .It Bq Er EINVAL A .Fa value structure specified a nanosecond value less than zero or greater than or equal to 1000 million, and the .Va it_value member of that structure did not specify zero seconds and nanoseconds. .El .Pp These system calls may fail if: .Bl -tag -width Er .It Bq Er EINVAL The .Fa timerid argument does not correspond to an ID returned by .Fn timer_create but not yet deleted by .Fn timer_delete . .El .Pp The .Fn timer_settime system call may fail if: .Bl -tag -width Er .It Bq Er EINVAL The .Va it_interval member of .Fa value is not zero and the timer was created with notification by creation of a new thread .Va ( sigev_sigev_notify was .Dv SIGEV_THREAD ) and a fixed stack address has been set in the thread attribute pointed to by .Va sigev_notify_attributes . .El .Pp The .Fn timer_gettime and .Fn timer_settime system calls may fail if: .Bl -tag -width Er .It Bq Er EFAULT Any arguments point outside the allocated address space or there is a memory protection fault. .El .Sh SEE ALSO .Xr clock_getres 2 , .Xr timer_create 2 , .Xr siginfo 3 .Sh STANDARDS The .Fn timer_getoverrun , .Fn timer_gettime , and .Fn timer_settime system calls conform to .St -p1003.1-2004 . .Sh HISTORY Support for .Tn POSIX per-process timer first appeared in .Fx 7.0 .