1 /*
2 * Copyright (c) 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 * @summary Test that a virtual thread waiting to enter a monitor, while pinning its
27 * carrier, will retry until it enters the monitor. This avoids starvation when the
28 * monitor is exited, an unmounted thread is the chosen successor, and the successor
29 * can't continue because there are no carriers available.
30 * @modules java.base/java.lang:+open
31 * @library /test/lib
32 * @requires vm.opt.LockingMode != 1
33 * @run main/othervm --enable-native-access=ALL-UNNAMED RetryMonitorEnterWhenPinned
34 */
35
36 import java.time.Duration;
37 import java.time.Instant;
38 import java.util.ArrayList;
39 import java.util.concurrent.CountDownLatch;
40 import java.util.concurrent.TimeUnit;
41 import jdk.test.lib.thread.VThreadPinner;
42
43 public class RetryMonitorEnterWhenPinned {
44 public static void main(String[] args) throws Exception {
45 int iterations = (args.length > 0) ? Integer.parseInt(args[0]) : 10;
46 for (int i = 1; i <= iterations; i++) {
47 System.out.printf("%s -- iteration %d --%n", Instant.now(), i);
48 run();
49 System.out.println();
50 }
51 }
52
53 static void run() throws Exception {
54 var threads = new ArrayList<Thread>();
55
56 Object lock = new Object();
57 synchronized (lock) {
58
59 // start virtual threads that block on monitorenter
60 for (int i = 0; i < 100; i++) {
61 var started = new CountDownLatch(1);
62 Thread thread = Thread.startVirtualThread(() -> {
63 started.countDown();
64 synchronized (lock) {
65 spin(20);
66 }
67 });
68
69 // wait for thread to start and block
70 started.await();
71 await(thread, Thread.State.BLOCKED);
72 threads.add(thread);
73 }
74
75 // start virtual threads that block on monitorenter while pinned
76 int carriersAvailable = Runtime.getRuntime().availableProcessors();
77 if (Thread.currentThread().isVirtual()) {
78 carriersAvailable--;
79 }
80 for (int i = 0; i < 100; i++) {
81 var started = new CountDownLatch(1);
82 Thread thread = Thread.startVirtualThread(() -> {
83 started.countDown();
84 VThreadPinner.runPinned(() -> {
85 synchronized (lock) {
86 spin(20);
87 }
88 });
89 });
90
91 // if there are carriers available when wait until the thread blocks.
92 if (carriersAvailable > 0) {
93 System.out.printf("%s waiting for thread #%d to block%n",
94 Instant.now(), thread.threadId());
95 started.await();
96 await(thread, Thread.State.BLOCKED);
97 carriersAvailable--;
98 }
99 threads.add(thread);
100 }
101
102 } // exit monitor
103
104 // wait for all threads to terminate
105 int threadsRemaining = threads.size();
106 while (threadsRemaining > 0) {
107 System.out.printf("%s waiting for %d threads to terminate%n",
108 Instant.now(), threadsRemaining);
109 int terminated = 0;
110 for (Thread t : threads) {
111 if (t.join(Duration.ofSeconds(1))) {
112 terminated++;
113 }
114 }
115 threadsRemaining = threads.size() - terminated;
116 }
117 System.out.printf("%s done%n", Instant.now());
118 }
119
120 /**
121 * Spin for the given number of milliseconds.
122 */
123 static void spin(long millis) {
124 long nanos = TimeUnit.MILLISECONDS.toNanos(millis);
125 long start = System.nanoTime();
126 while ((System.nanoTime() - start) < nanos) {
127 Thread.onSpinWait();
128 }
129 }
130
131 /**
132 * Wait for a thread to reach the expected state.
133 */
134 static void await(Thread thread, Thread.State expectedState) throws InterruptedException {
135 Thread.State state = thread.getState();
136 while (state != expectedState) {
137 assert state != Thread.State.TERMINATED : "Thread has terminated";
138 Thread.sleep(10);
139 state = thread.getState();
140 }
141 }
142 }