The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.


getitimer, setitimer - get and set value of interval timer


[XSI] [Option Start] #include <sys/time.h>

int getitimer(int
which, struct itimerval *value);
int setitimer(int
which, const struct itimerval *restrict value,
       struct itimerval *restrict
ovalue); [Option End]


The getitimer() function shall store the current value of the timer specified by which into the structure pointed to by value. The setitimer() function shall set the timer specified by which to the value specified in the structure pointed to by value, and if ovalue is not a null pointer, store the previous value of the timer in the structure pointed to by ovalue.

A timer value is defined by the itimerval structure, specified in <sys/time.h>. If it_value is non-zero, it shall indicate the time to the next timer expiration. If it_interval is non-zero, it shall specify a value to be used in reloading it_value when the timer expires. Setting it_value to 0 shall disable a timer, regardless of the value of it_interval. Setting it_interval to 0 shall disable a timer after its next expiration (assuming it_value is non-zero).

Implementations may place limitations on the granularity of timer values. For each interval timer, if the requested timer value requires a finer granularity than the implementation supports, the actual timer value shall be rounded up to the next supported value.

An XSI-conforming implementation provides each process with at least three interval timers, which are indicated by the which argument:

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.

The interaction between setitimer() and any of alarm(), sleep(), or usleep() is unspecified.


Upon successful completion, getitimer() or setitimer() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.


The setitimer() function shall fail if:

The value argument is not in canonical form. (In canonical form, the number of microseconds is a non-negative integer less than 1000000 and the number of seconds is a non-negative integer.)

The getitimer() and setitimer() functions may fail if:

The which argument is not recognized.

The following sections are informative.










alarm(), sleep(), timer_getoverrun(), ualarm(), usleep(), the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>, <sys/time.h>


First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Issue 6

The restrict keyword is added to the setitimer() prototype for alignment with the ISO/IEC 9899:1999 standard.

End of informative text.

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