CircularSet.java Source code

Introduction

Here is the source code for CircularSet.java

Source

// : c13:SerialNumberChecker.java
// Operations that may seem safe are not,
// when threads are present.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.

// Reuses storage so we don't run out of memory:

class CircularSet {
    private int[] array;

    private int len;

    private int index = 0;

    public CircularSet(int size) {
        array = new int[size];
        len = size;
        // Initialize to a value not produced
        // by the SerialNumberGenerator:
        for (int i = 0; i < size; i++)
            array[i] = -1;
    }

    public synchronized void add(int i) {
        array[index] = i;
        // Wrap index and write over old elements:
        index = ++index % len;
    }

    public synchronized boolean contains(int val) {
        for (int i = 0; i < len; i++)
            if (array[i] == val)
                return true;
        return false;
    }
}

public class SerialNumberChecker {
    private static CircularSet serials = new CircularSet(1000);

    static class SerialChecker extends Thread {
        SerialChecker() {
            start();
        }

        public void run() {
            while (true) {
                int serial = SerialNumberGenerator.nextSerialNumber();
                if (serials.contains(serial)) {
                    System.out.println("Duplicate: " + serial);
                    System.exit(0);
                }
                serials.add(serial);
            }
        }
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++)
            new SerialChecker();
        // Stop after 4 seconds:
        new Timeout(4000, "No duplicates detected");
    }
} ///:~

class SerialNumberGenerator {
    private static volatile int serialNumber = 0;

    public static int nextSerialNumber() {
        return serialNumber++;
    }
} ///:~

class Timeout extends java.util.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);
    }
} ///:~