1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95 29.\" $FreeBSD: src/lib/libc/sys/getitimer.2,v 1.10.2.6 2001/12/14 18:34:00 ru Exp $ 30.\" 31.Dd May 16, 1995 32.Dt GETITIMER 2 33.Os 34.Sh NAME 35.Nm getitimer , 36.Nm setitimer 37.Nd get/set value of interval timer 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/time.h 42.Fd "#define ITIMER_REAL 0" 43.Fd "#define ITIMER_VIRTUAL 1" 44.Fd "#define ITIMER_PROF 2" 45.Ft int 46.Fn getitimer "int which" "struct itimerval *value" 47.Ft int 48.Fn setitimer "int which" "const struct itimerval *value" "struct itimerval *ovalue" 49.Sh DESCRIPTION 50The system provides each process with three interval timers, 51defined in 52.In sys/time.h . 53The 54.Fn getitimer 55call returns the current value for the timer specified in 56.Fa which 57in the structure at 58.Fa value . 59The 60.Fn setitimer 61call sets a timer to the specified 62.Fa value 63(returning the previous value of the timer if 64.Fa ovalue 65is non-nil). 66.Pp 67A timer value is defined by the 68.Fa itimerval 69structure: 70.Bd -literal -offset indent 71struct itimerval { 72 struct timeval it_interval; /* timer interval */ 73 struct timeval it_value; /* current value */ 74}; 75.Ed 76.Pp 77If 78.Fa it_value 79is non-zero, it indicates the time to the next timer expiration. 80If 81.Fa it_interval 82is non-zero, it specifies a value to be used in reloading 83.Fa it_value 84when the timer expires. 85Setting 86.Fa it_value 87to 0 disables a timer, regardless of the value of 88.Fa it_interval . 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. A 102.Dv SIGALRM 103signal is 104delivered when this timer expires. 105.Pp 106The 107.Dv ITIMER_VIRTUAL 108timer decrements in process virtual time. 109It runs only when the process is executing. A 110.Dv SIGVTALRM 111signal 112is delivered when it expires. 113.Pp 114The 115.Dv ITIMER_PROF 116timer decrements both in process virtual time and 117when the system is running on behalf of the process. It is designed 118to be used by interpreters in statistically profiling the execution 119of interpreted programs. 120Each time the 121.Dv ITIMER_PROF 122timer expires, the 123.Dv SIGPROF 124signal is 125delivered. Because this signal may interrupt in-progress 126system calls, programs using this timer must be prepared to 127restart interrupted system calls. 128.Pp 129The maximum number of seconds allowed for 130.Fa it_interval 131and 132.Fa it_value 133in 134.Fn setitimer 135is 100000000. 136.Sh NOTES 137Three macros for manipulating time values are defined in 138.In sys/time.h . 139.Fa Timerclear 140sets a time value to zero, 141.Fa timerisset 142tests if a time value is non-zero, and 143.Fa timercmp 144compares two time values. 145.Sh RETURN VALUES 146.Rv -std 147.Sh ERRORS 148.Fn Getitimer 149and 150.Fn setitimer 151will fail if: 152.Bl -tag -width Er 153.It Bq Er EFAULT 154The 155.Fa value 156parameter specified a bad address. 157.It Bq Er EINVAL 158A 159.Fa value 160parameter specified a time that was too large 161to be handled. 162.El 163.Sh SEE ALSO 164.Xr gettimeofday 2 , 165.Xr select 2 , 166.Xr sigaction 2 , 167.Xr clocks 7 168.Sh HISTORY 169The 170.Fn getitimer 171function call appeared in 172.Bx 4.2 . 173