NAME

getitimer, setitimer − get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

int getitimer (which, value)
int which;
struct itimerval ∗value;

int setitimer (which, value, ovalue)
int which;
struct itimerval ∗value, ∗ovalue;

DESCRIPTION

The system provides each process with three interval timers, defined in <sys/time.h> as

ITIMER_REALreal time intervals
ITIMER_VIRTUAL virtual time intervals
ITIMER_PROFuser and system virtual time

The getitimer call returns the current value for the timer specified in which, while the setitimer call sets the value of a timer (optionally returning the previous value of the timer). 

A timer value is defined by the itimerval structure, whose members are:

structtimeval it_interval;/∗ timer interval ∗/
structtimeval it_value;/∗ current value ∗/

If it_value is non-zero, it indicates the time to the next timer expiration.  If it_interval is non-zero, it specifies a value to be used in reloading it_value when the timer expires.  Setting it_value to 0 disables a timer.  Setting it_interval to 0 causes a timer to be disabled after its next expiration (assuming it_value is non-zero). 

Time values smaller than the resolution of the system clock are rounded up to this resolution

The ITIMER_REAL timer decrements in real time.  A SIGALRM signal is delivered when this timer expires. 

The ITIMER_VIRTUAL timer decrements in process virtual time.  It runs only when the process is executing.  A SIGVTALRM signal is delivered when it expires. 

The 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 ITIMER_PROF timer expires, the 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. 

NOTES

Three macros for manipulating time values are defined in < sys/time.h >.  Timerclear sets a time value to zero, timerisset tests if a time value is non-zero, and timercmp compares two time values (beware that >= and <= do not work with this macro). 

RETURN VALUE

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 errno. 

ERRORS

The possible errors are:

[EFAULT] The value structure specified a bad address. 

[EINVAL] A value structure specified a time was too large to be handled. 

SEE ALSO

sigvec(2), gettimeofday(2)

CX/UX Programmer’s Reference Manual