Guten Tag,
das Problem ,dass ich momentan mit diesem Code habe, ist dass in dem Code irgendwo ein Read-Modify-Write Problem seien soll. Der Deadlock der momentan existiert ist gewollt ist nicht das Problem. Ich saß nun schon 2 Stunden vor diesem Code und hab überlegt wo der Fehler sein könnte, habe ihn aber nicht gefunden. Vielleicht hat eine von euch Glück 😉
das Problem ,dass ich momentan mit diesem Code habe, ist dass in dem Code irgendwo ein Read-Modify-Write Problem seien soll. Der Deadlock der momentan existiert ist gewollt ist nicht das Problem. Ich saß nun schon 2 Stunden vor diesem Code und hab überlegt wo der Fehler sein könnte, habe ihn aber nicht gefunden. Vielleicht hat eine von euch Glück 😉
Java:
package de.tuberlin.snet.prog2.ue04.philosophers;
import java.util.Random;
/**
* This class represents a philosopher. He is doing the following (in this order):
*
*/
public class Philosopher implements Runnable {
Chopstick leftChopstick;
Chopstick rightChopstick;
String name;
Random random = new Random();
public Philosopher(String name, Chopstick leftChopstick, Chopstick rightChopstick) {
this.name = name;
this.leftChopstick = leftChopstick;
this.rightChopstick = rightChopstick;
}
@Override
public void run() {
try {
while (true) {
leftChopstick.pickUp();
System.out.println(this + " picks up his left chopstick");
// to provoke a deadlock:
// Thread.yield();
rightChopstick.pickUp();
System.out.println(this + " picks up his right chopstick");
eat();
rightChopstick.putDown();
System.out.println(this + " puts down his right chopstick");
leftChopstick.putDown();
System.out.println(this + " puts down his left chopstick");
think();
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private void think() throws InterruptedException {
System.out.println(this + " is thinking");
Thread.sleep(random.nextInt(1000));
}
private void eat() throws InterruptedException {
System.out.println(this + " is eating");
Thread.sleep(random.nextInt(1000));
}
public String toString() {
return name;
}
}
Java:
package de.tuberlin.snet.prog2.ue04.philosophers;
/**
* This is an implementation of the dining philosophers problem.
* The given number of philosophers is created and started as threads.
*
*/
public class DiningPhilosophersProblem {
final int NUMBER_OF_PHILOSOPHERS = 5;
final String[] PHILOSOPHER_NAMES = {"Galilei", "Erasmus", "Dionysios", "Dewey", "Demokrit", "Cicero", "Bacon", "Aristoteles"};
Chopstick[] chopsticks;
Philosopher[] philosophers;
public DiningPhilosophersProblem() {
// prepare chopsticks
chopsticks = new Chopstick[NUMBER_OF_PHILOSOPHERS];
for (int i = 0; i < NUMBER_OF_PHILOSOPHERS; i++){
chopsticks[i] = new Chopstick();
}
// prepare philosophers
philosophers = new Philosopher[NUMBER_OF_PHILOSOPHERS];
for (int i = 0; i < NUMBER_OF_PHILOSOPHERS; i++){
String name;
if (i < PHILOSOPHER_NAMES.length)
name = PHILOSOPHER_NAMES[i] + "-" + i;
else
name = "Philosopher-i";
philosophers[i] = new Philosopher(name, chopsticks[i], chopsticks[(i+1) % NUMBER_OF_PHILOSOPHERS]);
}
// start philosophers
for (Philosopher phil: philosophers) {
new Thread(phil).start();
}
}
public static void main(String[] args) {
new DiningPhilosophersProblem();
}
}
Java:
package de.tuberlin.snet.prog2.ue04.philosophers;
/**
* Represents a chopstick used by the philosophers.
* If a philosopher holds the chopstick and another wants to
* pick it up he has to wait until the chopstick is free.
*
*
*
*/
public class Chopstick {
/** flag showing whether the chopstick is in use */
boolean inUse;
/**
* Waits until the chopstick is free and picks it up.
* @throws InterruptedException
*/
public void pickUp() throws InterruptedException {
while (isInUse()) {
Thread.sleep(100);
}
setInUse(true);
}
/**
* Puts the chopstick down so i can be used by another philosopher.
*/
public void putDown() {
setInUse(false);
}
/**
* Sets the {@link #inUse} variable.
* @param newValue
*/
private void setInUse(boolean newValue) {
inUse = newValue;
}
/**
* @return true, if the chopstick is in use, otherwise false
*/
private boolean isInUse() {
return inUse;
}
}
