.\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. 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, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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. .\" .\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95 .\" $FreeBSD: src/lib/libc/sys/getitimer.2,v 1.20 2004/07/02 23:52:13 ru Exp $ .\" .Dd May 16, 1995 .Dt GETITIMER 2 .Os .Sh NAME .Nm getitimer , .Nm setitimer .Nd get/set value of interval timer .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/time.h .Fd "#define ITIMER_REAL 0" .Fd "#define ITIMER_VIRTUAL 1" .Fd "#define ITIMER_PROF 2" .Ft int .Fn getitimer "int which" "struct itimerval *value" .Ft int .Fn setitimer "int which" "const struct itimerval *value" "struct itimerval *ovalue" .Sh DESCRIPTION The system provides each process with three interval timers, defined in .In sys/time.h . The .Fn getitimer system call returns the current value for the timer specified in .Fa which in the structure at .Fa value . The .Fn setitimer system call sets a timer to the specified .Fa value (returning the previous value of the timer if .Fa ovalue is non-nil). .Pp A timer value is defined by the .Fa itimerval structure: .Bd -literal -offset indent struct itimerval { struct timeval it_interval; /* timer interval */ struct timeval it_value; /* current value */ }; .Ed .Pp If .Fa it_value is non-zero, it indicates the time to the next timer expiration. If .Fa it_interval is non-zero, it specifies a value to be used in reloading .Fa it_value when the timer expires. Setting .Fa it_value to 0 disables a timer, regardless of the value of .Fa it_interval . Setting .Fa it_interval to 0 causes a timer to be disabled after its next expiration (assuming .Fa it_value is non-zero). .Pp Time values smaller than the resolution of the system clock are rounded up to this resolution (typically 10 milliseconds). .Pp The .Dv ITIMER_REAL timer decrements in real time. A .Dv SIGALRM signal is delivered when this timer expires. .Pp The .Dv ITIMER_VIRTUAL timer decrements in process virtual time. It runs only when the process is executing. A .Dv SIGVTALRM signal is delivered when it expires. .Pp The .Dv ITIMER_PROF timer decrements both in process virtual time and when the system is running on behalf of the process. It is designed to be used by interpreters in statistically profiling the execution of interpreted programs. Each time the .Dv ITIMER_PROF timer expires, the .Dv SIGPROF signal is delivered. Because this signal may interrupt in-progress system calls, programs using this timer must be prepared to restart interrupted system calls. .Pp The maximum number of seconds allowed for .Fa it_interval and .Fa it_value in .Fn setitimer is 100000000. .Sh NOTES Three macros for manipulating time values are defined in .In sys/time.h . The .Fn timerclear macro sets a time value to zero, .Fn timerisset tests if a time value is non-zero, and .Fn timercmp compares two time values. .Sh RETURN VALUES .Rv -std .Sh ERRORS The .Fn getitimer and .Fn setitimer system calls will fail if: .Bl -tag -width Er .It Bq Er EFAULT The .Fa value argument specified a bad address. .It Bq Er EINVAL The .Fa value argument specified a time that was too large to be handled. .El .Sh SEE ALSO .Xr gettimeofday 2 , .Xr select 2 , .Xr sigvec 2 , .Xr clocks 7 .Sh HISTORY The .Fn getitimer system call appeared in .Bx 4.2 .