/* File:  /home/faculty/liux/public_html/courses/cop4610/examples/sig_handle.cc
   Purpose: Demonstrate how to use signal for Cop4610,
   Author:  Xiuwen Liu, based on an example in Advanced Programming
            in the UNIX Environment, by W. Richard Stevens, 
            Addison-Wesley, 1992
   On the web: 
      http://www.cs.fsu.edu/~liux/courses/cop4610/examples/sig_handle.cc
   Compiling command:
     g++ -o sig_handle sig_handle.cc
   Exercise:
     ./sig_handle &
     Then try to send some signals to the running process using kill,
      for example (suppose the process id is 22502):
         kill -INT 22502
	 kill -USR1 22502
	 kill -QUIT 22502
	 kill -KILL 22502 (or kill -9 22502)
*/
/* Questions:
   1. What is a signal? What is an asynchronous event? What is an interrupt?
   2. Who is handling the signal? Who is running the sig_handler procedure
      when the running process receives a signal SIGINT?
   3. Suppose the processing id of the process is 22502. If we type
      kill -2 22502
      kill -2 22502
      Why is the response of the process different for the two cases?
   4. Why do people using "kill -9" to terminate a wild-running process?
*/
     
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <iostream.h>

void sig_handler(int); /* A signal handler example */
int i, j, k;
int interrupted;
int main(void)
{
  int anarray[100];
  int  interrupted=0;
  i = 0;
  j = 0;
  k = 0;
  /* Use signal to change the interpret handler for some signals */
  if (signal(SIGUSR1, sig_handler) == SIG_ERR) 
    cerr << getpid() << " Could not catch signal SIGUSR1." << endl;
  if (signal(SIGUSR2, sig_handler) == SIG_ERR) 
    cerr << getpid() << " Could not catch signal SIGUSR2." << endl;
  if (signal(SIGINT, sig_handler) == SIG_ERR) 
    cerr << getpid() << " Could not catch signal SIGUSR2." << endl;
  /*
  if (signal(SIGSEGV, sig_handler) == SIG_ERR) 
    cerr << getpid() << " Could not catch signal SIGSEGV." << endl;
  */
  for (;;) {
    i = 2000;
    k = 0;
    for (j=0; j < i; j++) {
      k += j;
    }
    i = 1980;

    k = 0;
    for (j=0; j < i; j++) {
      k += 2*j;
    }

    i = 2020;
    
    k = 0;
    for (j=0; j < i; j++) {
      k += j;
    }
    anarray[0] = 0; i =0;
    /*
    do {
      i++;
      anarray[i] = anarray[i-1]+2;
      if (i==0) break;
      if (interrupted !=0) break;
    } while(i >0 && interrupted ==0); 
    */
  }
}

void sig_handler(int signo) /* signo: Signal number defined in <signal.h>*/
{
  /* Reset to the interpret handler */
  signal(signo, sig_handler);
  switch(signo) {
  case SIGUSR1:
    cout << getpid() 
	 << ": Receieved signal SIGUSR1 = " << signo <<"." << endl;
    printf("Values of variables: i = %d j = %d k = %d.\n",
	   i, j, k);
    break;
  case SIGUSR2:
    cout << getpid()
	 << ": Receieved signal SIGUSR2 = " << signo <<"." << endl;
    printf("Values of variables: i = %d j = %d k = %d.\n",
	   i, j, k);
    break;  
  case SIGINT:
    cout << getpid() 
	 << ": Receieved signal SIGINT = " << signo <<"." << endl;
    printf("Values of variables: i = %d j = %d k = %d.\n",
	   i, j, k);
    break;  
  case SIGSEGV:
    interrupted = 1;
    cout << getpid() 
	 << ": Receieved signal SIGSEGV = " << signo <<"." << endl;
    printf("Values of variables: i = %d j = %d k = %d.\n",
	   i, j, k);
    i = 0;
    exit(0);
    break;  
  default:
    cout << getpid()
	 << ": Received signal " << signo << " with unknown type." 
	 << endl;
  }
  return;
}