#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/wait.h>

pid_t child_pid = 0;
int n = 0;

void process_a_ends(int sig)
{
	int status;

	if (kill(child_pid, SIGUSR2) < 0)
	{
		printf("Error sending SIGUSR2 to child\n");
		exit(2);
	}

	/* waiting for the child to end */

	wait(&status);
	printf("Child ended with code %d\n, WEXITSTATUS(status));

	printf("Process a ends.\n");
	exit(0);
}

void process_a()
{
	int i;

	if (signal(SIGINT, process_a_ends) == SIG_ERR)
	{
		printf("Error setting handler for SIGTERM\n");
		exit(1);
	}
	for (i = 0;;++)
	{
		usleep(1000);
		if (i%10 == 0)
			if (kill(child_pid, SIGUSR1) < 0)
			{
				printf("Error sending SIGUSR1 to child\n");
				exit(2);
			}
	}
}

void process_b_writes(int sig)
{
	printf("Process b received SIGUSR1: %d\n", ++n);
}

void process_b_ends(int sig)
{
	printf("Process b ends.\n");
	exit(0);
}

void process_b()
{
	/* Ignoring SIGINT. Process b will end only when receives SIGUSR2 */

	if (signal(SIGINT, SIG_IGN) == SIG_ERR)
	{
		printf("Error ignoring SIGINT in process b\n");
		exit(3);
	} 

	/* Setting the signal handlers */

	if (signal(SIGUSR1, process_b_writes) == SIG_ERR)
	{
		printf("Error setting handler for SIGUSR1\n");
		exit(4);
	}
	if (signal(SIGUSR2, process_b_ends) == SIG_ERR)
	{
		printf("Error setting handler for SIGUSR2\n");
		exit(5);
	}

	/* Infinite loop; 
		process b only responds to signals */

	while(1);
}

int main()
{
	int status;

	/* First, ignore the user signals,
	to prevent interrupting the child 
	process before setting the
	appropriate handlers */

	signal(SIGUSR1, SIG_IGN);
	signal(SIGUSR2, SIG_IGN);

	/* Creating the child process.
	A global variable 
	is used to store the child process ID
	in order to be able to use it from the 
	signal handlers */

	if ((child_pid = fork()) < 0)
	{
		printf("Error creating child process\n");
		exit(1);
	}

	if (child_pid == 0) /* the child process */
	{
		process_b();
		exit(0); 
	}
	else /* the parent process */
	{
		process_a();
	}

	/* this is still the parent code */
	
	return 0;
}