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

int x = 1;
void fork1()
{
    //int x = 1;
    pid_t pid = fork();
    if (pid == 0) {
        printf("Child has x = %d\n", ++x);
    } else {
        printf("Parent has x = %d\n", --x);
    }
    printf("Bye from process %d with x = %d\n", getpid(), x);
}

void fork2()
{
    printf("L0\n");
    fork();
    printf("L1\n");    
    fork();
    printf("Bye\n");
}

void fork3()
{
    printf("L0\n");
    fork();
    printf("L1\n");    
    fork();
    printf("L2\n");    
    fork();
    printf("Bye\n");
}

void fork4()
{
    printf("L0\n");
    if (fork() != 0) {
        printf("L1\n");    
        if (fork() != 0) {
            printf("L2\n");
            fork();
        }
    }
    printf("Bye\n");
}

void fork5()
{
    printf("L0\n");
    if (fork() == 0) {
        printf("L1\n");    
        if (fork() == 0) {
            printf("L2\n");
            fork();
        }
    }
    printf("Bye\n");
}

void cleanup(void) {
    printf("Cleaning up\n");
}

void fork6()
{
    atexit(cleanup);
    fork();
    exit(0);
}

void fork7()
{
    if (fork() == 0) {
        printf("Terminating Child, PID = %d\n", getpid());
        exit(0);
    } else {
        printf("Running Parent, PID = %d\n", getpid());
        while (1)
            ; /* Infinite loop */
    }
}

void fork8()
{
    if (fork() == 0) {
    /* Child */
        printf("Running Child, PID = %d\n",
            getpid());
        while (1)
            ; /* Infinite loop */
    } else {
        printf("Terminating Parent, PID = %d\n",
            getpid());
        exit(0);
    }
}

void fork9()
{
    int child_status;

    if (fork() == 0) {
        printf("HC: hello from child\n");
    } else {
        printf("HP: hello from parent\n");
        wait(&child_status);
        printf("CT: child has terminated\n");
    }
    printf("Bye\n");
}

#define N 5
void fork10()
{
    pid_t pid[N];
    int i;
    int child_status;
    for (i = 0; i < N; i++)
        if ((pid[i] = fork()) == 0) {
            sleep(1);
            exit(100+i); /* Child */
        }
            
    for (i = 0; i < N; i++) {
        pid_t wpid = wait(&child_status);
        if (WIFEXITED(child_status))
            printf("Child %d terminated with exit status %d\n",
                   wpid, WEXITSTATUS(child_status));
        else
            printf("Child %d terminate abnormally\n", wpid);
    }
}

void fork11()
{
    pid_t pid[N];
    int i;
    int child_status;
    for (i = 0; i < N; i++)
        if ((pid[i] = fork()) == 0) {
            sleep(1);
            exit(100+i); /* Child */
        }
    for (i = 0; i < N; i++) {
        pid_t wpid = waitpid(pid[i], &child_status, 0);
        if (WIFEXITED(child_status))
            printf("Child %d terminated with exit status %d\n",
                wpid, WEXITSTATUS(child_status));
        else
            printf("Child %d terminate abnormally\n", wpid);
    }
}

void fork12()
{
    pid_t pid[N];
    int i;
    int child_status;
    for (i = 0; i < N; i++)
        if ((pid[i] = fork()) == 0) {
            /* Child: Infinite Loop */
            while(1)
                ;
        }
    for (i = 0; i < N; i++) {
        printf("Killing process %d\n", pid[i]);
        kill(pid[i], SIGINT);
    }
    for (i = 0; i < N; i++) {
        pid_t wpid = wait(&child_status);
        if (WIFEXITED(child_status))
            printf("Child %d terminated with exit status %d\n",
            wpid, WEXITSTATUS(child_status));
        else
            printf("Child %d terminated abnormally\n", wpid);
    }
}

void int_handler(int sig)
{
    printf("Process %d received signal %d\n", getpid(), sig);
    exit(0);
}

void fork13()
{
    pid_t pid[N];
    int i;
    int child_status;
    signal(SIGINT, int_handler);
    for (i = 0; i < N; i++)
        if ((pid[i] = fork()) == 0) {
            /* Child: Infinite Loop */
            while(1)
                ;
        }
    for (i = 0; i < N; i++) {
        printf("Killing process %d\n", pid[i]);
        kill(pid[i], SIGINT);
    }
    for (i = 0; i < N; i++) {
        pid_t wpid = wait(&child_status);
        if (WIFEXITED(child_status))
            printf("Child %d terminated with exit status %d\n",
            wpid, WEXITSTATUS(child_status));
        else
            printf("Child %d terminated abnormally\n", wpid);
    }
    while(1);
}

int ccount = 0;
void child_handler(int sig)
{
    int child_status;
    pid_t pid = wait(&child_status);
    ccount--;
    printf("Received signal %d from process %d\n", sig, pid);
}

void fork14()
{
    pid_t pid[N];
    int i;
    ccount = N;
    signal(SIGCHLD, child_handler);
    for (i = 0; i < N; i++)
    if ((pid[i] = fork()) == 0) {
        printf("Child: pid=%d\n", getpid());
        /* Child: Exit */
        exit(0);
    }
    while (ccount > 0)
        pause();
}

void child_handler2(int sig)
{
    int child_status;
    pid_t pid;
    while ((pid = wait(&child_status)) > 0) {
        ccount--;
        printf("Received signal %d from process %d\n", sig, pid);
    }
}

void fork15()
{
    pid_t pid[N];
    int i;
    ccount = N;

    signal(SIGCHLD, child_handler2);
    for (i = 0; i < N; i++)
    if ((pid[i] = fork()) == 0) {
        printf("Child: pid=%d\n", getpid());
        /* Child: Exit */
        exit(0);
    }
    while (ccount > 0) {
        pause();
    }
}

void fork16() 
{
    pid_t pid;
    if ((pid = fork()) == 0) {
        printf("Child: pid=%d pgrp=%d\n", getpid(), getpgrp());
        while (1);
    } else {
        if ((pid = fork()) == 0) {
            printf("Child: pid=%d pgrp=%d\n", getpid(), getpgrp());
            while (1);
        }
    }
}

void fork17() 
{
    pid_t pid;
    if ((pid = fork()) == 0) {
        printf("Child: pid=%d pgrp=%d\n", getpid(), getpgrp());
        while (1);
    } else {
        printf("Parent: pid=%d pgrp=%d\n", getpid(), getpgrp());
        while (1);
    }
}

int main(int argc, char *argv[])
{
    int option = 0;
    if (argc > 1)
         option = atoi(argv[1]);
    switch(option) {
        case 1: fork1();
        break;
        case 2: fork2();
        break;
        case 3: fork3();
        break;
        case 4: fork4();
        break;
        case 5: fork5();
        break;
        case 6: fork6();
        break;
        case 7: fork7();
        break;
        case 8: fork8();
        break;
        case 9: fork9();
        break;
        case 10: fork10();
        break;
        case 11: fork11();
        break;
        case 12: fork12();
        break;
        case 13: fork13();
        break;
        case 14: fork14();
        break;
        case 15: fork15();
        break;
        case 16: fork16();
        break;
        case 17: fork17();
        break;
        default:
        printf("Unknown option %d\n", option);
        break;
    }
    return 0;
}