SIGALARM

[mmque]

When we put alarm() in the program. Do we know we get signal SIGALARM or not, if we ignore this signal?

 

[marsd]

Try running this little program and determine for yourself.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <signal.h>


#define MAX 15
#define SIG 14
//function protos
void catchCall(int);
int *retnewArray(int);
void printArray(int *,int);
//global counter
int COUNTER = 0;

int main(void) {
int p = 0, v;
int *pp;
          //init
          srand(time(NULL));
          signal(SIG,SIG_IGN);
         //end init
          while (p < MAX) {
                v = (1 + rand() % MAX);
                pp = retnewArray(v);
                if (v % 2 == 1) {
                    alarm(1);
                    signal(SIG,SIG_IGN);
                    printf(&quot;Set alarm with SIG_IGN\n&quot;,v);
                } 
                if (v % 2 == 0) {
                    printf(&quot;Installing new handler.\n&quot;,v);
                    alarm(1);
                    signal(SIG,catchCall);
                    COUNTER++;
                }
                printArray(pp,v);
                sleep(1);
                free(pp);
                p++;    
            }
printf(&quot;Saw %d user handled alarms from %d possible\n&quot;, COUNTER,MAX);
return 0;
}

                     
void catchCall(int sig) {
       printf(&quot;Alarm() popped\n&quot;);
}      
        

int *retnewArray(int num) {
int i = 0;
int *new = malloc(num * sizeof(int));

            if (!new) {return NULL;}
            for (i=0 ; i < num ; i++) {
                new[i] = (1 + rand() % MAX);
            }
            return new;
}


void printArray(int *parr, int n) {
int y = 0;

            while (y < n) {
                  printf(&quot;%d at element %d\n&quot;,parr[y],y);
                  ++y;
            }
}