1 /*
 2  * Copyright (c) 2004, 2024, Oracle and/or its affiliates. All rights reserved.
 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 4  *
 5  * This code is free software; you can redistribute it and/or modify it
 6  * under the terms of the GNU General Public License version 2 only, as
 7  * published by the Free Software Foundation.
 8  *
 9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  */
23 
24 /*
25  * @test
26  * @bug 8322732
27  * @summary ForkJoinPool utilizes available workers even with arbitrary task dependencies
28  */
29 import java.util.concurrent.Callable;
30 import java.util.concurrent.ForkJoinPool;
31 import java.util.concurrent.ForkJoinTask;
32 import java.util.concurrent.atomic.AtomicInteger;
33 
34 public class Starvation {
35     static final AtomicInteger count = new AtomicInteger();
36     static final Callable<Void> noop = new Callable<Void>() {
37             public Void call() {
38                 return null; }};
39     static final class AwaitCount implements Callable<Void> {
40         private volatile int c;
41         AwaitCount(int c) { this.c = c; }
42         public Void call() {
43             while (count.get() == c) Thread.onSpinWait();
44             return null; }};
45 
46     public static void main(String[] args) throws Exception {
47         try (var pool = new ForkJoinPool(2)) {
48             for (int i = 0; i < 100_000; i++) {
49                 var future1 = pool.submit(new AwaitCount(i));
50                 var future2 = pool.submit(ForkJoinTask.adapt(noop));
51                 future2.get();
52                 count.set(i + 1);
53                 future1.get();
54             }
55         }
56     }
57 }