getitimer(3C)

get/set value of interval timer

From the original Amiga UNIX 2.1 manual. Some things it mentions may not be in this release.

NAME

getitimer, setitimer - get/set value of interval timer

SYNOPSIS

#include <sys/time.h>
int getitimer(int which, struct itimerval *value);
int setitimer(int which, struct itimerval *value, struct itimerval
    *ovalue);

DESCRIPTION

     The system provides each process with three interval timers,
     defined  in  sys/time.h.   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  struc-
     ture  pointed to by ovalue.  A timer value is defined by the
     itimerval structure [see gettimeofday(3C) 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
it_interval.  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:

ITIMER_REAL Decrements in real time. A SIGALRM signal is delivered when this timer expires.

ITIMER_VIRTUAL Decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered when it expires.

ITIMER_PROF 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.

DIAGNOSTICS

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:

EINVAL 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.

NOTES