Question

How to change this C code to java?

dining_philosopher.c

#define N 5 /* number of philosophers */ void philosopher(int i) /* i: philosopher number, from 0 to 4 */ { while (TRUE) { think(); /* philosopher is thinking */ take_fork(i); /* take left fork */ take_fork((i+1) % N); /* take right fork; % is modulo operator */ eat(); /* yum-yum, spaghetti */ put_fork(i); /* put left fork back on the table */ put_fork((i+1) % N); /* put right fork back on the table */ } }

dining_philosopher_semaphore.c

#define N        5               /* number of philosophers */
#define LEFT     (i + N - 1) % N /* number of i's left neighbor */
#define RIGHT    (i + 1) % N     /* number of i's right neighbor */
#define THINKING 0               /* philosopher is thinking */
#define HUNGRY   1               /* philosopher is trying to get forks */
#define EATING   2               /* philosopher is eating */

typedef int semaphore;           /* semaphores are a special kind of int */
int state[N];                    /* array to keep track of everyone's state */
semaphore mutex = 1 ;            /* mutual exclusion for critical regions */
semaphore s[N];                  /* one semaphore per philosopher */

void philosopher(int i)          /* i: philosopher number, from 0 to N-1 */
{
    while (TRUE) {               /* repeat forever */
        think( );                /* philosopher is thinking */
        take_forks(i);           /* acquire two forks or block */
        eat();                   /* yum-yum, spaghetti */
        put_forks(i);            /* put both forks back on table */
    }
}

void take_forks(int i)           /* i: philosopher number, from 0 to N-1 */
{
    down(&mutex);                /* enter critical region */
    state[i] = HUNGRY;           /* record fact that philosopher i is hungry */
    test(i);                     /* try to acquire 2 forks */
    up(&mutex);                  /* exit critical region */
    down(&s[i]);                 /* block if forks were not acquired */
}

void put_forks(i)                /* i: philosopher number, from 0 to N-1 */
{
    down(&mutex);                /* enter critical region */
    state[i] = THINKING;         /* philosopher has finished eating */
    test(LEFT);                  /* see if left neighbor can now eat */
    test(RIGHT);                 /* see if right neighbor can now eat */
    up(&mutex);                  /* exit critical region */
}

void test(i)                     /* i: philosopher number, from 0 to N-1 */
{
    if(state[i] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING) {
        state[i] = EATING;
        up(&s[i]);
    }
}

Answer 1

For changing the code from C to Java you can implement dining philosopher problem using Java.

Below is the Java code for solving Dining Philosopher problem.

Code:

import java.util.concurrent.Semaphore;
import java.util.concurrent.ThreadLocalRandom;

public class Main {

static int philosopher = 5;
static philosopher philosophers[] = new philosopher[philosopher];
static chopstick chopsticks[] = new chopstick[philosopher];

static class chopstick {

public Semaphore mutex = new Semaphore(1);

void grab() {
try {
mutex.acquire();
}
catch (Exception e) {
e.printStackTrace(System.out);
}
}

void release() {
mutex.release();
}

boolean isFree() {
return mutex.availablePermits() > 0;
}

}

static class philosopher extends Thread {

public int number;
public chopstick leftchopstick;
public chopstick rightchopstick;

philosopher(int num, chopstick left, chopstick right) {
number = num;
leftchopstick = left;
rightchopstick = right;
}

public void run(){

while (true) {
leftchopstick.grab();
System.out.println("philosopher " + (number+1) + " grabs left chopstick.");
rightchopstick.grab();
System.out.println("philosopher " + (number+1) + " grabs right chopstick.");
eat();
leftchopstick.release();
System.out.println("philosopher " + (number+1) + " releases left chopstick.");
rightchopstick.release();
System.out.println("philosopher " + (number+1) + " releases right chopstick.");
}
}

void eat() {
try {
int sleepTime = ThreadLocalRandom.current().nextInt(0, 1000);
System.out.println("philosopher " + (number+1) + " eats for " + sleepTime);
Thread.sleep(sleepTime);
}
catch (Exception e) {
e.printStackTrace(System.out);
}
}

}

public static void main(String argv[]) {

for (int i = 0; i < philosopher; i++) {
chopsticks[i] = new chopstick();
}

for (int i = 0; i < philosopher; i++) {
philosophers[i] = new philosopher(i, chopsticks[i], chopsticks[(i + 1) % philosopher]);
philosophers[i].start();
}

while (true) {
try {
// sleep 1 sec
Thread.sleep(1000);

// check for deadlock
boolean deadlock = true;
for (chopstick f : chopsticks) {
if (f.isFree()) {
deadlock = false;
break;
}
}
if (deadlock) {
Thread.sleep(1000);
System.out.println("Everyone Eats");
break;
}
}
catch (Exception e) {
e.printStackTrace(System.out);
}
}

System.out.println("Exit The Program!");
System.exit(0);
}

}

Output Screenshot:

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