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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95 33.\" 34.Dd May 16, 1995 35.Dt GETITIMER 2 36.Os BSD 4.2 37.Sh NAME 38.Nm getitimer , 39.Nm setitimer 40.Nd get/set value of interval timer 41.Sh SYNOPSIS 42.Fd #include <sys/time.h> 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.Ao Pa sys/time.h Ac . 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-nil). 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, regardless of the value of 89.Fa it_interval . 90Setting 91.Fa it_interval 92to 0 causes a timer to be disabled after its next expiration (assuming 93.Fa it_value 94is non-zero). 95.Pp 96Time values smaller than the resolution of the 97system clock are rounded up to this resolution 98(typically 10 milliseconds). 99.Pp 100The 101.Dv ITIMER_REAL 102timer decrements in real time. A 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. A 111.Dv SIGVTALRM 112signal 113is 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. It is designed 119to be used by interpreters in statistically profiling the execution 120of interpreted programs. 121Each time the 122.Dv ITIMER_PROF 123timer expires, the 124.Dv SIGPROF 125signal is 126delivered. Because this signal may interrupt in-progress 127system calls, programs using this timer must be prepared to 128restart interrupted system calls. 129.Pp 130The maximum number of seconds allowed for 131.Fa it_interval 132and 133.Fa it_value 134in 135.Fn setitimer 136is 100000000. 137.Sh NOTES 138Three macros for manipulating time values are defined in 139.Ao Pa sys/time.h Ac . 140.Fa Timerclear 141sets a time value to zero, 142.Fa timerisset 143tests if a time value is non-zero, and 144.Fa timercmp 145compares two time values. 146.Sh RETURN VALUES 147If the calls succeed, a value of 0 is returned. If an error occurs, 148the value -1 is returned, and a more precise error code is placed 149in the global variable 150.Va errno . 151.Sh ERRORS 152.Fn Getitimer 153and 154.Fn setitimer 155will fail if: 156.Bl -tag -width Er 157.It Bq Er EFAULT 158The 159.Fa value 160parameter specified a bad address. 161.It Bq Er EINVAL 162A 163.Fa value 164parameter specified a time that was too large 165to be handled. 166.El 167.Sh SEE ALSO 168.Xr gettimeofday 2 , 169.Xr select 2 , 170.Xr sigvec 2 , 171.Xr clocks 7 172.Sh HISTORY 173The 174.Fn getitimer 175function call appeared in 176.Bx 4.2 . 177