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@(#)getitimer.2 8.2 (Berkeley) 12/11/93
.Dd December 11, 1993 .Dt GETITIMER 2 .Os BSD 4.2 .Sh NAME .Nm getitimer , .Nm setitimer .Nd get/set value of interval timer .Sh SYNOPSIS .Fd #include <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" "struct itimerval *value" "struct itimerval *ovalue" .Sh DESCRIPTION The system provides each process with three interval timers, defined in .Ao Pa sys/time.h Ac . The .Fn getitimer call returns the current value for the timer specified in .Fa which in the structure at .Fa value . The .Fn setitimer call sets a timer to the specified .Fa value (returning the previous value of the timer if .Fa ovalue is non-nil).
p A timer value is defined by the .Fa itimerval structure: d -literal -offset indent struct itimerval { struct timeval it_interval; /* timer interval */ struct timeval it_value; /* current value */ }; .Ed
p 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. Setting .Fa it_interval to 0 causes a timer to be disabled after its next expiration (assuming .Fa it_value is non-zero).
p Time values smaller than the resolution of the system clock are rounded up to this resolution (typically 10 milliseconds).
p The .Dv ITIMER_REAL timer decrements in real time. A .Dv SIGALRM signal is delivered when this timer expires.
p 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.
p 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. .Sh NOTES Three macros for manipulating time values are defined in .Ao Pa sys/time.h Ac . .Fa Timerclear sets a time value to zero, .Fa timerisset tests if a time value is non-zero, and .Fa timercmp compares two time values (beware that >= and <= do not work with this macro). .Sh RETURN VALUES If the calls succeed, a value of 0 is returned. If an error occurs, the value -1 is returned, and a more precise error code is placed in the global variable .Va errno . .Sh ERRORS .Fn Getitimer and .Fn setitimer will fail if: l -tag -width Er t Bq Er EFAULT The .Fa value parameter specified a bad address. t Bq Er EINVAL A .Fa value parameter specified a time that was too large to be handled. .El .Sh SEE ALSO .Xr select 2 , .Xr sigvec 2 , .Xr gettimeofday 2 , .Xr clocks 7 .Sh HISTORY The .Nm function call appeared in x 4.2 .