96 lines
3.0 KiB
Java
96 lines
3.0 KiB
Java
// concurrency/SemaphoreDemo.java
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// ©2016 MindView LLC: see Copyright.txt
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// Testing the Pool class
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import java.util.concurrent.*;
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import java.util.*;
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// A task to check a resource out of a pool:
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class CheckoutTask<T> implements Runnable {
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private static int counter = 0;
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private final int id = counter++;
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private Pool<T> pool;
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public CheckoutTask(Pool<T> pool) {
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this.pool = pool;
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}
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@Override
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public void run() {
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try {
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T item = pool.checkOut();
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System.out.println(this + "checked out " + item);
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TimeUnit.SECONDS.sleep(1);
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System.out.println(this +"checking in " + item);
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pool.checkIn(item);
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} catch(InterruptedException e) {
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// Acceptable way to terminate
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}
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}
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@Override
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public String toString() {
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return "CheckoutTask " + id + " ";
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}
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}
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public class SemaphoreDemo {
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final static int SIZE = 25;
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public static void
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main(String[] args) throws Exception {
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final Pool<Fat> pool = new Pool<>(Fat.class, SIZE);
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ExecutorService exec = Executors.newCachedThreadPool();
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for(int i = 0; i < SIZE; i++)
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exec.execute(new CheckoutTask<>(pool));
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System.out.println("All CheckoutTasks created");
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List<Fat> list = new ArrayList<>();
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for(int i = 0; i < SIZE; i++) {
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Fat f = pool.checkOut();
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System.out.print(i + ": main() thread checked out ");
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f.operation();
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list.add(f);
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}
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Future<?> blocked = exec.submit(() -> {
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try {
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// Semaphore prevents additional checkout,
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// so call is blocked:
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pool.checkOut();
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} catch(InterruptedException e) {
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System.out.println("checkOut() Interrupted");
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}
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});
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TimeUnit.SECONDS.sleep(2);
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blocked.cancel(true); // Break out of blocked call
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System.out.println("Checking in objects in " + list);
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for(Fat f : list)
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pool.checkIn(f);
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for(Fat f : list)
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pool.checkIn(f); // Second checkIn ignored
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exec.shutdown();
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}
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}
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/* Output: (First and last 10 Lines)
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CheckoutTask 4 checked out Fat id: 2
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CheckoutTask 22 checked out Fat id: 24
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CheckoutTask 14 checked out Fat id: 23
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CheckoutTask 21 checked out Fat id: 22
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CheckoutTask 18 checked out Fat id: 21
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CheckoutTask 17 checked out Fat id: 20
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CheckoutTask 10 checked out Fat id: 19
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CheckoutTask 13 checked out Fat id: 18
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CheckoutTask 9 checked out Fat id: 17
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CheckoutTask 6 checked out Fat id: 16
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________...________...________...________...________
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20: main() thread checked out Fat id: 5
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21: main() thread checked out Fat id: 1
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CheckoutTask 7 checking in Fat id: 3
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CheckoutTask 0 checking in Fat id: 0
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CheckoutTask 8 checking in Fat id: 4
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22: main() thread checked out Fat id: 3
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23: main() thread checked out Fat id: 0
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24: main() thread checked out Fat id: 4
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checkOut() Interrupted
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Checking in objects in [Fat id: 2, Fat id: 23, Fat id: 24,
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Fat id: 22, Fat id: 21, Fat id: 20, Fat id: 19, Fat id: 18,
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Fat id: 17, Fat id: 16, Fat id: 15, Fat id: 14, Fat id: 13,
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Fat id: 11, Fat id: 12, Fat id: 9, Fat id: 10, Fat id: 8,
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Fat id: 7, Fat id: 6, Fat id: 5, Fat id: 1, Fat id: 3, Fat
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id: 0, Fat id: 4]
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*/
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