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. 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.
COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- 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 .