get value of interval timer
int getitimer(int which, struct itimerval value);
int setitimer(int which, struct itimerval value,
struct itimerval ovalue);
The system provides each process with three interval timers, defined in
The getitimer call stores the current value of the timer specified by
which into the structure pointed to by value.
The setitimer call sets the value of the timer specified by
which to the value specified in the structure pointed to by
value, and if ovalue is not NULL, stores the previous value
of the timer in the structure pointed to by ovalue.
A timer value is defined by the itimerval structure
for the definition of timeval],
which includes the following members:
struct timeval it_interval; / timer interval /
struct timeval it_value; / current value /
If it_value is non-zero, it indicates the time to the next timer expiration.
If it_interval is non-zero, it specifies a value to be used in reloading
it_value when the timer expires.
Setting it_value to zero disables a timer, regardless of the value of
Setting it_interval to zero disables a timer after its next expiration
(assuming it_value is non-zero).
Time values smaller than the resolution of the
system clock are rounded up to this resolution.
The three timers are:
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.
If the calls succeed, a value of 0 is returned.
If an error occurs, the value -1 is returned, and an error code is placed in
the global variable errno.
Under the following conditions, the functions getitimer and setitimer
fail and set errno to:
The specified number of seconds is greater than 100,000,000,
the number of microseconds is greater than or equal to 1,000,000,
or the which parameter is unrecognized.
The microseconds field should not be equal to or greater than one second.
setitimer is independent of the alarm system call.
Do not use setitimer with the sleep routine.
A sleep following a setitimer
wipes out knowledge of the user signal handler.
Considerations for threads programming
There is a separate interval timer per thread and the subsequent
signal is delivered to the requesting thread;
however, only the real time variant (ITIMER_REAL) is supported.
Considerations for lightweight processes
The kernel maintains separate timers per LWP.
The SIGALARM, SIGVTALRM and SIGPROF are
posted to the individual LWP that set the timers.
The Threads Library has
``wrapper'' functions for getitimer and setitimer
that direct actions to the correct thread.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004