111 lines
2.6 KiB
Java
111 lines
2.6 KiB
Java
// concurrency/ReaderWriterList.java
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// ©2016 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://mindviewinc.com/Books/OnJava/ for more book information.
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import java.util.concurrent.*;
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import java.util.concurrent.locks.*;
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import java.util.*;
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public class ReaderWriterList<T> {
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private ArrayList<T> lockedList;
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// Make the ordering fair:
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private ReentrantReadWriteLock lock =
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new ReentrantReadWriteLock(true);
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public ReaderWriterList(int size, T initialValue) {
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lockedList = new ArrayList<>(
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Collections.nCopies(size, initialValue));
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}
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public T set(int index, T element) {
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Lock wlock = lock.writeLock();
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wlock.lock();
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try {
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return lockedList.set(index, element);
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} finally {
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wlock.unlock();
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}
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}
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public T get(int index) {
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Lock rlock = lock.readLock();
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rlock.lock();
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try {
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// Show that multiple readers
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// can acquire the read lock:
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if(lock.getReadLockCount() > 1)
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System.out.println(lock.getReadLockCount());
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return lockedList.get(index);
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} finally {
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rlock.unlock();
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}
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}
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public static void main(String[] args) throws Exception {
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new ReaderWriterListTest(30, 1);
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}
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}
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class ReaderWriterListTest {
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ExecutorService exec = Executors.newCachedThreadPool();
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private final static int SIZE = 100;
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private static Random rand = new Random(47);
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private ReaderWriterList<Integer> list =
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new ReaderWriterList<>(SIZE, 0);
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private class Writer implements Runnable {
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@Override
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public void run() {
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try {
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for(int i = 0; i < 20; i++) { // 2 second test
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list.set(i, rand.nextInt());
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TimeUnit.MILLISECONDS.sleep(100);
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}
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} catch(InterruptedException e) {
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// Acceptable way to exit
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}
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System.out.println("Writer finished, shutting down");
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exec.shutdownNow();
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}
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}
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private class Reader implements Runnable {
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@Override
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public void run() {
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try {
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while(!Thread.interrupted()) {
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for(int i = 0; i < SIZE; i++) {
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list.get(i);
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TimeUnit.MILLISECONDS.sleep(1);
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}
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}
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} catch(InterruptedException e) {
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// Acceptable way to exit
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}
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}
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}
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public ReaderWriterListTest(int readers, int writers) {
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for(int i = 0; i < readers; i++)
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exec.execute(new Reader());
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for(int i = 0; i < writers; i++)
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exec.execute(new Writer());
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}
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}
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/* Output: (First and last 10 Lines)
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6
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15
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14
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13
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12
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11
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10
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9
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8
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5
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________...________...________...________...________
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21
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30
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29
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28
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28
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30
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29
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28
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27
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26
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*/
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