Programming

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <signal.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define true 1
#define false 0


pid_t pid_child2=0, pid_child1=0, pid_parent=0;
sigset_t pMask, pOldMask, cMask, cOldMask;
int child1_ready=0, child2_ready=0;

/* signal handler for parent */
void sig_parent(int sig)
{
  if ((sig==SIGUSR2) && (child1_ready==0)) {
      child1_ready=1;
      printf("* Parent: child1 is ready\n");
      kill(pid_child1, SIGUSR1); 	// send SIGUSR1 to child1
  } else
  if (sig==SIGUSR2) {
      printf("Parent: received signal from child1, do something\n");
      printf("*** Parent end ***\n");
      exit(0);
  }
  return;
}

/* signal handler for child1 */
void sig_child1(int sig)
{
  if (sig==SIGUSR1) {
      printf("Child1: received signal from parent, do something\n");
      kill(pid_child2, SIGUSR1); // send SIGUSR1 to child2
  } else
  if ((sig==SIGUSR2) && (child2_ready==0)) {
      child2_ready=1;
      printf("* Child1: child2 is ready\n");
      kill(pid_parent, SIGUSR2); 	// inform parent
  } else
  if (sig==SIGUSR2) {
      printf("*** child1 end***\n");
      kill(pid_parent, SIGUSR2);	// inform parent
      exit(0);
  }
  
  return;
}

void sig_child2(int sig)
{
  if (sig==SIGUSR1) {
      printf("Child2: received signal from child1, do something\n");
      kill(pid_child1, SIGUSR2);	// inform child1
      printf("*** child2 end ***\n");
      exit(0);
  } else
  if (sig==SIGUSR2) {
      printf("* Child2: sending SIGUSR2 to child1\n");
      kill(pid_child1, SIGUSR2); 	// inform child1
  }  
  return;
}

/* child2 code */
void child2(void)
{
  pid_child1=getppid(); 			// child2 knows its parent (child1)
  if (signal(SIGUSR1, sig_child2)==SIG_ERR) {
    fprintf(stderr, "Can't catch SIGUSR1.");
  }
  if (signal(SIGUSR2, sig_child2)==SIG_ERR) {
    fprintf(stderr, "Can't catch SIGUSR2.");
  }
  sig_child2(SIGUSR2); 				// start the communication
  for (;;) sigsuspend(&cOldMask);  		// wait for signal
}


void child1(void)
{
  pid_parent=getppid(); 			// child1 knows its parent (parent)

  sigemptyset(&cMask);
  sigaddset(&cMask, SIGUSR1);
  sigaddset(&cMask, SIGUSR2);
  sigprocmask(SIG_BLOCK, &cMask, &cOldMask);


  pid_t pid=fork(); 

  if (pid==0) {     			// we are in the child process
    child2();
  } else {
    if (pid>0) {   			// we are in the parent process
      pid_child2=pid;
      if (signal(SIGUSR1, sig_child1)==SIG_ERR) { 
        fprintf(stderr, "Can't catch SIGUSR1.");
      }
      if (signal(SIGUSR2, sig_child1)==SIG_ERR) {
        fprintf(stderr, "Can't catch SIGUSR2.");
      }
      for (;;) {			// wait for signals
        sigsuspend(&pOldMask);   		
        sigsuspend(&cOldMask);
      }
    } else {
      fprintf(stderr, "Can't create new child.");
    }
  }

  sigprocmask(SIG_UNBLOCK, &cMask, NULL); 
  return;
}

void parent(void)
{
  sigemptyset(&pMask);
  sigaddset(&pMask, SIGUSR1);
  sigaddset(&pMask, SIGUSR2);
  sigprocmask(SIG_BLOCK, &pMask, &pOldMask); 

  pid_t pid=fork(); 

  if (pid==0) {     			// we are in child process
    child1();
  } else {
    if (pid>0) {   			// we are in parent process
      pid_child1=pid;
      if (signal(SIGUSR2, sig_parent)==SIG_ERR) {
        fprintf(stderr, "Can't catch SIGUSR2.");
      }
      for (;;) sigsuspend(&pOldMask);   		// wait for signal
    } else {  
      fprintf(stderr, "Can't create new child.");
    }
  }
  sigprocmask(SIG_UNBLOCK, &pMask, NULL);
  return;
}

int main()
{
  setbuf(stdout,NULL);

  parent();
    
  return 0;
}