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
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22  */
23 
24 /**
25  * @test
26  * @summary Test unblocking a virtual thread waiting to enter a monitor
27  * @key randomness
28  * @modules java.base/java.lang:+open
29  * @library /test/lib
30  * @run junit MonitorUnblocking
31  */
32 
33 import java.util.concurrent.CountDownLatch;
34 import java.util.concurrent.ThreadLocalRandom;
35 
36 import jdk.test.lib.thread.VThreadRunner;
37 import org.junit.jupiter.api.RepeatedTest;
38 import static org.junit.jupiter.api.Assertions.*;
39 
40 class MonitorUnblocking {
41 
42     /**
43      * Test unblocking a virtual thread waiting to enter a monitor held by a platform thread.
44      */
45     @RepeatedTest(50)
46     void testUnblocking() throws Exception {
47         var lock = new Object();
48         var started = new CountDownLatch(1);
49         var vthread = Thread.ofVirtual().unstarted(() -> {
50             started.countDown();
51             synchronized (lock) {
52                 // do nothing
53             }
54         });
55         try {
56             synchronized (lock) {
57                 vthread.start();
58                 started.await();
59 
60                 // random delay before exiting monitor
61                 switch (ThreadLocalRandom.current().nextInt(4)) {
62                     case 0 -> { /* no delay */}
63                     case 1 -> Thread.onSpinWait();
64                     case 2 -> Thread.yield();
65                     case 3 -> await(vthread, Thread.State.BLOCKED);
66                     default -> fail();
67                 }
68             }
69         } finally {
70             vthread.join();
71         }
72     }
73 
74     /**
75      * Test unblocking a virtual thread waiting to enter a monitor held by another
76      * virtual thread.
77      */
78     @RepeatedTest(50)
79     void testUnblocking2() throws Exception {
80         // need at least two carrier threads
81         int previousParallelism = VThreadRunner.ensureParallelism(2);
82         try {
83             VThreadRunner.run(this::testUnblocking);
84         } finally {
85             VThreadRunner.setParallelism(previousParallelism);
86         }
87     }
88 
89     private void await(Thread thread, Thread.State expectedState) {
90         Thread.State state = thread.getState();
91         while (state != expectedState) {
92             assertTrue(state != Thread.State.TERMINATED, "Thread has terminated");
93             Thread.yield();
94             state = thread.getState();
95         }
96     }
97 }