// : c13:diningphilosophers.java
// demonstrates how deadlock can be hidden in a program.
// {args: 5 0 deadlock 4}
// from 'thinking in java, 3rd ed.' (c) bruce eckel 2002
// www.bruceeckel.com. see copyright notice in copyright.txt.
import java.util.random;
import java.util.timer;
import java.util.timertask;
class chopstick {
private static int counter = 0;
private int number = counter++;
public string tostring() {
return "chopstick " + number;
}
}
class philosopher extends thread {
private static random rand = new random();
private static int counter = 0;
private int number = counter++;
private chopstick leftchopstick;
private chopstick rightchopstick;
static int ponder = 0; // package access
public philosopher(chopstick left, chopstick right) {
leftchopstick = left;
rightchopstick = right;
start();
}
public void think() {
system.out.println(this + " thinking");
if (ponder > 0)
try {
sleep(rand.nextint(ponder));
} catch (interruptedexception e) {
throw new runtimeexception(e);
}
}
public void eat() {
synchronized (leftchopstick) {
system.out.println(this + " has " + this.leftchopstick
+ " waiting for " + this.rightchopstick);
synchronized (rightchopstick) {
system.out.println(this + " eating");
}
}
}
public string tostring() {
return "philosopher " + number;
}
public void run() {
while (true) {
think();
eat();
}
}
}
public class diningphilosophers {
public static void main(string[] args) {
if (args.length < 3) {
system.err.println("usage:/n"
+ "java diningphilosophers numberofphilosophers "
+ "ponderfactor deadlock timeout/n"
+ "a nonzero ponderfactor will generate a random "
+ "sleep time during think()./n"
+ "if deadlock is not the string "
+ "'deadlock', the program will not deadlock./n"
+ "a nonzero timeout will stop the program after "
+ "that number of seconds.");
system.exit(1);
}
philosopher[] philosopher = new philosopher[integer.parseint(args[0])];
philosopher.ponder = integer.parseint(args[1]);
chopstick left = new chopstick(), right = new chopstick(), first = left;
int i = 0;
while (i < philosopher.length - 1) {
philosopher[i++] = new philosopher(left, right);
left = right;
right = new chopstick();
}
if (args[2].equals("deadlock"))
philosopher[i] = new philosopher(left, first);
else
// swapping values prevents deadlock:
philosopher[i] = new philosopher(first, left);
// optionally break out of program:
if (args.length >= 4) {
int delay = integer.parseint(args[3]);
if (delay != 0)
new timeout(delay * 1000, "timed out");
}
}
} ///:~
class timeout extends timer {
public timeout(int delay, final string msg) {
super(true); // daemon thread
schedule(new timertask() {
public void run() {
system.out.println(msg);
system.exit(0);
}
}, delay);
}
} ///:~ |
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