OSF

NAME

setitimer, getitimer −  Sets or returns the value of interval timers

SYNOPSIS

#include <sys/time.h> #define ITIMER_REAL   0
#define ITIMER_VIRTUAL1
#define ITIMER_PROF   2 int setitimer(
int which,
struct itimerval ∗value,
struct itimerval ∗ovalue) ; int getitimer(
int which,
struct itimerval ∗value) ;

PARAMETERS

whichIdentifies the interval timer. This parameter may be expressed as one of three symbolic constants: ITIMER_REAL, ITIMER_VIRTUAL, and ITIMER_PROF. 

valuePoints to an itimerval structure whose members specify a timer interval and the time left to the end of the interval. 

ovaluePoints to an itimerval structure whose members specify a current timer interval and the time left to the end of the interval. 

DESCRIPTION

The getitimer() function returns the current value for the timer specified by the which parameter in the structure pointed to by the value parameter. 

The setitimer() function sets a timer to the specified value (returning the previous value of the timer if ovalue is nonzero). 

A timer value is defined by the itimerval structure: struct itimerval {
structtimeval it_interval;
structtimeval it_value;
};

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

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

The system provides each process with three interval timers, defined in the sys/time.h header file:

       •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 the sys/time.h header file.  The timerclear() macro sets a time value to zero, the timerisset() macro tests if a time value is nonzero, and the timercmp() macro compares two time values.  Beware that the comparisons >= and <= do not work with the timercmp() macro. 

RETURN VALUES

Upon successful completion, the value 0 (zero) is returned.  Otherwise, -1 is returned and errno is set to indicate the error. 

ERRORS

If the getitimer() or setitimer() function fails, errno may be set to one of the following values:

[EFAULT]The value parameter specified a bad address. 

[EINVAL]The value parameter specified a time that was too large to be handled. 

RELATED INFORMATION

Functions: gettimeofday(2)