#include <sys/time.h>
int setitimer( int which,
const struct itimerval *value,
struct itimerval *ovalue );
The setitimer() function sets the timer specified by which to the value in the structure pointed to by value and stores the previous value of the timer in the structure pointed to by ovalue.
None.
The possible values for which, which are defined in the <sys/time.h> header file, are as follows:
| ITIMER_REAL | The interval timer value is decremented in real time. The SIGALRM signal is generated for the process when this timer expires. |
| ITIMER_VIRTUAL | The interval timer value is only decremented when the process is running. The SIGVTALRM signal is generated for the process when this timer expires. |
| ITIMER_PROF | The interval timer value is only decremented when the process is running or when the system is running on behalf of the process. The SIGPROF signal is generated for the process when this timer expires. |
The 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 indicates the time to be used to reset the timer when the it_value time elapses. If it_value is zero, the timer is disabled and the value of it_interval is ignored. If it_interval is zero, the timer is disabled after the next timer expiration.
| 0 | setitimer() was successful. |
| -1 | setitimer() was not successful. The errno variable is set to indicate the error. |
If setitimer() is not successful, errno usually indicates the following error. Under some conditions, errno could indicate an error other than that listed here.
The value specified for the argument is not correct.
A function was passed incorrect argument values, or an operation was attempted on an object and the operation specified is not supported for that type of object.
An argument value is not valid, out of range, or NULL.
System resources not available to complete request.
Process not enabled for signals.
An attempt was made to call a signal function under one of the following conditions:
The setitimer() function enables a process for signals if the process is not already enabled for signals. For details, see Qp0sEnableSignals()--Enable Process for Signals. If the system has not been enabled for signals, setitimer() is not successful, and an [ENOTSIGINIT] error is returned.
See Code disclaimer information for information pertaining to code examples.
The following example returns the current interval timer value using the setitimer() function:
#include <sys/time.h>
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <time.h>
#include <errno.h>
#define LOOP_LIMIT 1E12
volatile int sigcount=0;
void catcher( int sig ) {
struct itimerval value;
int which = ITIMER_REAL;
printf( "Signal catcher called for signal %d\n", sig );
sigcount++;
if( sigcount > 1 ) {
/*
* Disable the real time interval timer
*/
getitimer( which, &value );
value.it_value.tv_sec = 0;
value.it_value.tv_usec = 0;
setitimer( which, &value, NULL );
}
}
int main( int argc, char *argv[] ) {
int result = 0;
struct itimerval value, ovalue, pvalue;
int which = ITIMER_REAL;
struct sigaction sact;
volatile double count;
time_t t;
sigemptyset( &sact.sa_mask );
sact.sa_flags = 0;
sact.sa_handler = catcher;
sigaction( SIGALRM, &sact, NULL );
getitimer( which, &pvalue );
/*
* Set a real time interval timer to repeat every 200 milliseconds
*/
value.it_interval.tv_sec = 0; /* Zero seconds */
value.it_interval.tv_usec = 200000; /* Two hundred milliseconds */
value.it_value.tv_sec = 0; /* Zero seconds */
value.it_value.tv_usec = 500000; /* Five hundred milliseconds */
result = setitimer( which, &value, &ovalue );
/*
* The interval timer value returned by setitimer() should be
* identical to the timer value returned by getitimer().
*/
if( ovalue.it_interval.tv_sec != pvalue.it_interval.tv_sec ||
ovalue.it_interval.tv_usec != pvalue.it_interval.tv_usec ||
ovalue.it_value.tv_sec != pvalue.it_value.tv_sec ||
ovalue.it_value.tv_usec != pvalue.it_value.tv_usec ) {
printf( "Real time interval timer mismatch\n" );
result = -1;
}
time( &t );
printf( "Before loop, time is %s", ctime(&t) );
for( count=0; ((count<LOOP_LIMIT) && (sigcount<2)); count++ );
time( &t );
printf( "After loop, time is %s\n", ctime(&t) );
if( sigcount == 0 )
printf( "The signal catcher never gained control\n" );
else
printf( "The signal catcher gained control\n" );
printf( "The value of count is %.0f\n", count );
return( result );
}
Before loop, time is Sun Jun 15 10:14:00 1997
Signal catcher called for signal 14
Signal catcher called for signal 14
After loop, time is Sun Jun 15 10:14:01 1997
The signal catcher gained control
The value of count is 702943
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