#include <unistd.h> unsigned int alarm( unsigned int seconds );
The alarm() function generates a SIGALRM signal after the number of seconds specified by the seconds parameter have elapsed. The delivery of the SIGALRM signal is directed at the calling process.
seconds is the number of real seconds to elapse before the SIGALRM is generated. Because of processor delays, the SIGALRM may be generated slightly later than this specified time. If seconds is zero, any previously set alarm request is canceled.
Only one such alarm can be active at a time for the process. If a new alarm time is set, any previous alarm is canceled.
None.
| value | alarm() was successful. The
value returned is one of the following:
|
| -1 | alarm() was not successful. The errno variable is set to indicate the error. |
If alarm() is not successful, errno usually indicates the following error. Under some conditions, errno could indicate an error other than that listed here.
Process not enabled for signals.
An attempt was made to call a signal function under one of the following conditions:
The alarm() 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, alarm() is not successful, and an [ENOTSIGINIT] error is returned.
The following example generates a SIGALRM signal using the alarm() function.
Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <time.h>
#include <errno.h>
#define LOOP_LIMIT 1E6
volatile int sigcount=0;
void catcher( int sig ) {
printf( "Signal catcher called for signal %d\n", sig );
sigcount = 1;
}
int main( int argc, char *argv[] ) {
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 );
alarm(5); /* timer will pop in five seconds */
time( &t );
printf( "Before loop, time is %s", ctime(&t) );
for( count=0; ((count<LOOP_LIMIT) && (sigcount==0)); 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( 0 );
}
Before loop, time is Sun Jan 22 10:14:00 1995
Signal catcher called for signal 14
After loop, time is Sun Jan 22 10:14:05 1995
The signal catcher gained control
The value of count is 290032