GETITIMER

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

BSD mandoc
BSD 4.2

NAME

getitimer setitimer - get/set value of interval timer

SYNOPSIS

Fd #include <sys/time.h> Fd #define ITIMER_REAL 0 Fd #define ITIMER_VIRTUAL 1 Fd #define ITIMER_PROF2 Ft int Fn getitimer int which struct itimerval *value Ft int Fn setitimer int which struct itimerval *value struct itimerval *ovalue

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).

A timer value is defined by the Fa itimerval structure:

struct itimerval {
        struct  timeval it_interval;    /* timer interval */
        struct  timeval it_value;       /* current value */
};

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).

Time values smaller than the resolution of the system clock are rounded up to this resolution (typically 10 milliseconds).

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 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).

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 errno

ERRORS

Fn Getitimer and Fn setitimer will fail if:

Bq Er EFAULT: The Fa value parameter specified a bad address.
Bq Er EINVAL: A Fa value parameter specified a time that was too large to be handled.

HISTORY

The Fn getitimer function call appeared in BSD 4.2

This document was created by man2html, using the manual pages.
Time: 16:28:59 GMT, April 18, 2022