1 /*
 2  * Copyright (c) 2023, 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  * @summary Stress test Thread.getStackTrace on virtual threads that are blocking or
27  *     blocked on monitorenter
28  */
29 
30 import java.time.Duration;
31 import java.util.concurrent.ThreadLocalRandom;
32 import java.util.concurrent.atomic.AtomicBoolean;
33 
34 public class GetStackTraceALotWhenBlocked {
35     static final long DURATION_IN_NANOS = Duration.ofSeconds(10).toNanos();
36 
37     public static void main(String[] args) throws Exception {
38         var done = new AtomicBoolean();
39         var lock = new Object();
40 
41         Runnable task = () -> {
42             long count = 0L;
43             while (!done.get()) {
44                 synchronized (lock) {
45                     pause();
46                 }
47                 count++;
48             }
49             System.out.format("%s => %d%n", Thread.currentThread(), count);
50         };
51 
52         var thread1 = Thread.ofVirtual().start(task);
53         var thread2 = Thread.ofVirtual().start(task);
54         try {
55             long startTime = System.nanoTime();
56             while ((System.nanoTime() - startTime) < DURATION_IN_NANOS) {
57                 thread1.getStackTrace();
58                 pause();
59                 thread2.getStackTrace();
60                 pause();
61             }
62         } finally {
63             done.set(true);
64             thread1.join();
65             thread2.join();
66         }
67     }
68 
69     private static void pause() {
70         if (ThreadLocalRandom.current().nextBoolean()) {
71             Thread.onSpinWait();
72         } else {
73             Thread.yield();
74         }
75     }
76 }