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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.\" $FreeBSD$ 30.\" 31.Dd May 1, 2020 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 55system call returns the current value for the timer specified in 56.Fa which 57in the structure at 58.Fa value . 59The 60.Fn setitimer 61system call sets a timer to the specified 62.Fa value 63(returning the previous value of the timer if 64.Fa ovalue 65is not a null pointer). 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. 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 114is delivered when it expires. 115.Pp 116The 117.Dv ITIMER_PROF 118timer decrements both in process virtual time and 119when the system is running on behalf of the process. 120It is designed 121to be used by interpreters in statistically profiling the execution 122of interpreted programs. 123Each time the 124.Dv ITIMER_PROF 125timer expires, the 126.Dv SIGPROF 127signal is 128delivered. 129Because this signal may interrupt in-progress 130system calls, programs using this timer must be prepared to 131restart interrupted system calls. 132.Pp 133The maximum number of seconds allowed for 134.Fa it_interval 135and 136.Fa it_value 137in 138.Fn setitimer 139is 100000000. 140.Sh NOTES 141Three macros for manipulating time values are defined in 142.In sys/time.h . 143The 144.Fn timerclear 145macro 146sets a time value to zero, 147.Fn timerisset 148tests if a time value is non-zero, and 149.Fn timercmp 150compares two time values. 151.Sh RETURN VALUES 152.Rv -std 153.Sh ERRORS 154The 155.Fn getitimer 156and 157.Fn setitimer 158system calls 159will fail if: 160.Bl -tag -width Er 161.It Bq Er EFAULT 162The 163.Fa value 164argument specified a bad address. 165.It Bq Er EINVAL 166The 167.Fa value 168argument specified a time that was too large 169to be handled. 170.El 171.Sh SEE ALSO 172.Xr gettimeofday 2 , 173.Xr select 2 , 174.Xr sigaction 2 , 175.Xr clocks 7 176.Sh STANDARDS 177The 178.Fn getitimer 179and 180.Fn setitimer 181functions conform to 182.St -p1003.1-2001 . 183The later 184.St -p1003.1-2008 185revision however marked both functions as obsolescent, 186recommending the use of 187.Xr timer_gettime 2 188and 189.Xr timer_settime 2 190instead. 191.Sh HISTORY 192The 193.Fn getitimer 194system call appeared in 195.Bx 4.2 . 196