// File :sigmenu.cpp
// Menu driven program to demonstrate sigprocmask(), sigaction() and ?
// sigsuspend & sigpending, along with masks and other stuff.
// User is allowed to specify signals to block, catch, or suspend. After the 
// 	request, the signal will be sent to itself to see what happens.
// The previous action for all signals will be maintained.

// Stop this program using kill -9 <pid>

#include <sys/types.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <iostream>
#define  period 3

using namespace std;

char menu();
void getSignal(int &);

void handler(int);

main()
{struct sigaction defaultAction[32],action;
 sigset_t sigset,oldset,pendingset;
 // First, set up default action array. For each signal, reset it's action,
 //  which places the default action into the 3rd argument of sigaction()
 // Put the action to be the handler.
 action.sa_handler = (void (*)(int))handler;
 int i;
 for (i=1;i<32;i++) {
  	if (sigaction(i,&action,&defaultAction[i])<0) {
		cerr << i << " couldn't be caught\n";
	}
	// Now, restore the default action	
  	if (sigaction(i,&defaultAction[i],NULL)<0) {
		cerr << i << " couldn't be reset to its default\n";
	}
 }
 int signalNum;
 char choice;
 // Empty out the signal set
 sigemptyset(&sigset);
 do  {
	choice=menu();
	if (choice=='B' || choice=='C' || choice=='S')
	 	getSignal(signalNum);
 	switch (choice) {
		case 'B':
		  sigaddset(&sigset,signalNum);
		  sigprocmask(SIG_BLOCK,&sigset,&oldset);
		  cout << "Mask set. Signal will be issued in 1 second\n";
		  sleep(1);
		  kill(getpid(),signalNum);
		  cout << "Check what's pending...";
		  sigpending(&pendingset);
		  for (i=1;i<32;i++)
		    if (sigismember(&pendingset,i))
			cout << i << " ";
		  cout << endl;
		  cout << "Now, the signal will be unblocked...\n";
		  sigprocmask(SIG_UNBLOCK,&sigset,&oldset);
		  // Restore sigset
		  sigdelset(&sigset,signalNum);
		  break;
		case 'C':
		  cout << "The handler will be set...\n"; 
		  sigaction(signalNum,&action,NULL);
		  cout << "The signal will be sent in 1 second\n";
		  sleep(1);
		  kill(getpid(),signalNum);
		  cout << "And, we're back...Default action restored\n";
  		  if (sigaction(signalNum,&defaultAction[signalNum],NULL)<0) {
		    cerr << i << " couldn't be reset to its default\n";
		  }
		  break;
	}
 } while (choice !='Q');
}

char getChoice(char *ok)
{char ch;
 do ch=toupper(cin.get()); while (strchr(ok,ch)==NULL);
 return(toupper(ch));
}

char menu()
{cout << "\n===================================================\n";
 cout << "Enter Choice:\n";
 cout << "B)lock a signal\n";
 cout << "C)atch a signal\n";
 cout << "Q)uit\n";
 cout << "===================================================\n";
 return(getChoice("BCQ"));
}

void getSignal(int &theSignal)
{cout << "Enter the signal number, a value in range [1,31] >";
 cin >> theSignal;
}
void handler(int sig)
{fprintf(stderr,"Caught Signal %d\n",sig);
}