Content-type: text/html Man page of getitimer

getitimer

Section: System Calls (2)
Index Return to Main Contents
 

NAME

getitimer, setitimer - Returns or sets the value of interval timers  

SYNOPSIS

#include <sys/time.h>

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

int setitimer(
        int which,
        const struct itimerval *value,
        struct itimerval *ovalue) ;

The following definition of the setitimer() function does not conform to current standards and is supported only for backward compatibility:

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

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

getitimer(), setitimer():  XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.  

PARAMETERS

Identifies the interval timer. This parameter may be expressed as one of three symbolic constants: ITIMER_REAL, ITIMER_VIRTUAL, and ITIMER_PROF. Points to an itimerval structure whose members specify a timer interval and the time left to the end of the interval. Points 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 the timer specified by which 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 {        struct  timeval it_interval;
       struct  timeval 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: Decrements in real time. A SIGALRM signal is delivered when this timer expires. Decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered when it expires. 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

The following information applies only to the backward-compatible versions of the getitimer() and setitimer() functions.

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

The setitimer() function sets errno to the specified values for the following conditions: [Digital]  The value parameter specified a bad address. The value parameter specified a time that was too large to be handled, or was a negative time value, or the which value is not defined.

The getitimer() function sets errno to the specified values for the following conditions: [Digital]  The value parameter specified a bad address. The which value is not defined.

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

RELATED INFORMATION

Functions: gettimeofday(2)

Standards: standards(5) delim off


 

Index

NAME
SYNOPSIS
STANDARDS
PARAMETERS
DESCRIPTION
NOTES
RETURN VALUES
ERRORS
RELATED INFORMATION

This document was created by man2html, using the manual pages.
Time: 02:40:14 GMT, October 02, 2010