NAME

getitimer, setitimer − get/set value of interval timer

SYNOPSIS

#include <time.h>

int getitimer(int which, struct itimerval *value);

int setitimer(

int which,
const struct itimerval *value,
struct itimerval *ovalue

);

DESCRIPTION

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

A timer value is defined by the itimerval structure.  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  0  disables  a timer, regardless of the value of it_interval. Setting it_interval to 0 disables 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 will 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:

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. 

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

RETURN VALUE

Upon successful completion, getitimer() or setitimer() returns  0. Otherwise, -1 is returned and errno is set to indicate the error. 

ERRORS

The setitimer() function will 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 1,000,000 and the number of seconds is a non-negative integer.) 

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

 [EINVAL] The which argument is not recognised. 

SEE ALSO

alarm() , sleep() , ualarm() , usleep() , <signal.h>, <sys/time.h>. 

CHANGE HISTORY

First released in Issue 4, Version 2. 

HP−UX EXTENSIONS

DESCRIPTION

A timer value is defined by the itimerval structure:

struct itimerval {
   struct timeval   it_interval;    /* timer interval */
   struct timeval   it_value;       /* current value */
};

Time values smaller than the resolution of the system clock are rounded up to this resolution.  The machine-dependent clock resolution is 1/HZ seconds, where the constant HZ is defined in <sys/param.h>.  Time values larger than an implementation-specific maximum value are rounded down to this maximum.  The maximum values for the three interval timers are specified by the constants MAX_ALARM, MAX_VTALARM, and MAX_PROF defined in <sys/param.h>.  On all implementations, these values are guaranteed to be at least 31 days (in seconds). 

Each time the ITIMER_PROF timer expires, the SIGPROF signal is delivered.  Since this signal can interrupt in-progress system calls, programs using this timer must be prepared to restart interrupted system calls. 

Interval timers are not inherited by a child process across a fork(), but are inherited across an exec(). 

Three macros for manipulating time values are defined in <time.h>:

timerclear Set a time value to zero. 

timerisset Test if a time value is non-zero. 

timercmp Compare two time values.  (Beware that >= and <= do not work with the timercmp macro.) 

The timer used with ITIMER_REAL is also used by alarm() (see alarm(2)). Thus successive calls to alarm(), getitimer(), and setitimer() set and return the state of a single timer.  In addition, a call to alarm() sets the timer interval to zero. 

ERRORS

getitimer() or setitimer() fail if any of the following conditions are encountered:

[EFAULT] The value structure specified a bad address.  Reliable detection of this error is implementation dependent. 

[EINVAL] A value structure specified a microsecond value less that zero or greater than or equal to one million. 

[EINVAL] which does not specify one of the three possible timers. 

EXAMPLES

The following call to setitimer() sets the real-time interval timer to expire initially after 10 seconds and every 0.5 seconds thereafter:

struct itimerval rttimer;
struct itimerval old_rttimer;

rttimer.it_value.tv_sec     = 10;
rttimer.it_value.tv_usec    = 0;
rttimer.it_interval.tv_sec  = 0;
rttimer.it_interval.tv_usec = 500000;

setitimer (ITIMER_REAL, &rttimer, &old_rttimer);

AUTHOR

getitimer() was developed by the University of California, Berkeley. 

SEE ALSO

alarm(2) , exec(2) , gettimeofday(2) , signal(5). 

Hewlett-Packard Company  —  HP-UX Release 10.20:  July 1996