1.\" $OpenBSD: getitimer.2,v 1.32 2019/02/07 02:56:13 cheloha Exp $ 2.\" $NetBSD: getitimer.2,v 1.6 1995/10/12 15:40:54 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)getitimer.2 8.2 (Berkeley) 12/11/93 32.\" 33.Dd $Mdocdate: February 7 2019 $ 34.Dt GETITIMER 2 35.Os 36.Sh NAME 37.Nm getitimer , 38.Nm setitimer 39.Nd get/set value of interval timer 40.Sh SYNOPSIS 41.In sys/time.h 42.Pp 43.Fd #define ITIMER_REAL 0 44.Fd #define ITIMER_VIRTUAL 1 45.Fd #define ITIMER_PROF 2 46.Ft int 47.Fn getitimer "int which" "struct itimerval *value" 48.Ft int 49.Fn setitimer "int which" "const struct itimerval *value" "struct itimerval *ovalue" 50.Sh DESCRIPTION 51The system provides each process with three interval timers, 52defined in 53.In sys/time.h . 54The 55.Fn getitimer 56call returns the current value for the timer specified in 57.Fa which 58in the structure at 59.Fa value . 60The 61.Fn setitimer 62call sets a timer to the specified 63.Fa value 64(returning the previous value of the timer if 65.Fa ovalue 66is non-null). 67.Pp 68A timer value is defined by the 69.Fa itimerval 70structure: 71.Bd -literal -offset indent 72struct itimerval { 73 struct timeval it_interval; /* timer interval */ 74 struct timeval it_value; /* current value */ 75}; 76.Ed 77.Pp 78If 79.Fa it_value 80is non-zero, it indicates the time to the next timer expiration. 81If 82.Fa it_interval 83is non-zero, it specifies a value to be used in reloading 84.Fa it_value 85when the timer expires. 86Setting 87.Fa it_value 88to 0 disables a timer. 89Setting 90.Fa it_interval 91to 0 causes a timer to be disabled after its next expiration (assuming 92.Fa it_value 93is non-zero). 94.Pp 95Time values smaller than the resolution of the 96system clock are rounded up to this resolution 97(typically 10 milliseconds). 98.Pp 99The 100.Dv ITIMER_REAL 101timer decrements in real time. 102A 103.Dv SIGALRM 104signal is 105delivered when this timer expires. 106.Pp 107The 108.Dv ITIMER_VIRTUAL 109timer decrements in process virtual time. 110It runs only when the process is executing. 111A 112.Dv SIGVTALRM 113signal is delivered when it expires. 114.Pp 115The 116.Dv ITIMER_PROF 117timer decrements both in process virtual time and 118when the system is running on behalf of the process. 119It is designed to be used by interpreters in statistically profiling 120the execution of interpreted programs. 121Each time the 122.Dv ITIMER_PROF 123timer expires, the 124.Dv SIGPROF 125signal is delivered. 126Because this signal may interrupt in-progress 127system calls, programs using this timer must be prepared to 128restart interrupted system calls. 129.Sh ERRORS 130.Fn getitimer 131and 132.Fn setitimer 133will fail if: 134.Bl -tag -width Er 135.It Bq Er EFAULT 136The 137.Fa value 138parameter specified a bad address. 139.It Bq Er EINVAL 140An unrecognized value for 141.Fa which 142was specified. 143.El 144.Pp 145In addition, 146.Fn setitimer 147may return the following error: 148.Bl -tag -width Er 149.It Bq Er EINVAL 150.Fa value 151or 152.Fa ovalue 153specified a time that was too large to be handled. 154.El 155.Sh SEE ALSO 156.Xr clock_gettime 2 , 157.Xr gettimeofday 2 , 158.Xr poll 2 , 159.Xr select 2 , 160.Xr sigaction 2 161.Sh STANDARDS 162The 163.Fn getitimer 164and 165.Fn setitimer 166functions conform to 167.St -p1003.1-2008 . 168.Sh HISTORY 169The 170.Fn getitimer 171and 172.Fn setitimer 173system calls first appeared in 174.Bx 4.1c . 175