GETITIMER(P) POSIX Programmer's Manual GETITIMER(P)
getitimer, setitimer - get and set value of interval timer
int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *restrict value,
struct itimerval *restrict ovalue);
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. Set-
ting 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 inter-
preters in statistically profiling the execution of interpreted programs. Each time the ITIMER_PROF timer expires, the SIGPROF sig-
nal 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:
EINVAL 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:
EINVAL 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>,
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 GETITIMER(P)