59 lines
1.5 KiB
Java
59 lines
1.5 KiB
Java
// lowlevel/SerialNumberChecker.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Operations that might seem safe are not,
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// when threads are present.
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import java.util.*;
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import java.util.concurrent.*;
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import onjava.Nap;
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// Reuses storage so we don't run out of memory:
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class CircularSet {
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private int[] array;
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private int size;
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private int index = 0;
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public CircularSet(int size) {
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array = new int[size];
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// Initialize to a value not produced
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// by the SerialNumberSupplier:
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Arrays.fill(array, -1);
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this.size = size;
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}
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public synchronized void add(int i) {
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array[index] = i;
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// Wrap index and write over old elements:
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index = ++index % size;
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}
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public synchronized boolean contains(int val) {
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for(int i = 0; i < size; i++)
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if(array[i] == val) return true;
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return false;
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}
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}
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public class SerialNumberChecker implements Runnable {
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private CircularSet serials = new CircularSet(1000);
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@Override
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public void run() {
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while(true) {
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int serial =
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SerialNumberSupplier.nextSerialNumber();
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if(serials.contains(serial)) {
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System.out.println("Duplicate: " + serial);
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System.exit(0);
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}
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serials.add(serial);
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}
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}
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public static void main(String[] args) {
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for(int i = 0; i < 10; i++)
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CompletableFuture.runAsync(
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new SerialNumberChecker());
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new Nap(4000, "No duplicates detected");
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}
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}
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/* Output:
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Duplicate: 4119
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*/
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