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 * @run main/othervm --enable-native-access=ALL-UNNAMED BusyMonitorEnterWhenPinned
33 */
34
35 import java.time.Duration;
36 import java.time.Instant;
37 import java.util.ArrayList;
38 import java.util.concurrent.CountDownLatch;
39 import java.util.concurrent.TimeUnit;
40 import jdk.test.lib.thread.VThreadPinner;
41
42 public class BusyMonitorEnterWhenPinned {
43 public static void main(String[] args) throws Exception {
44 int iterations = (args.length > 0) ? Integer.parseInt(args[0]) : 10;
45 for (int i = 1; i <= iterations; i++) {
46 System.out.printf("%s -- iteration %d --%n", Instant.now(), i);
47 run();
48 System.out.println();
49 }
50 }
51
52 static void run() throws Exception {
53 var threads = new ArrayList<Thread>();
54
55 Object lock = new Object();
56 synchronized (lock) {
57
58 // start virtual threads that block on monitorenter
59 for (int i = 0; i < 100; i++) {
60 var started = new CountDownLatch(1);
61 Thread thread = Thread.startVirtualThread(() -> {
62 started.countDown();
63 synchronized (lock) {
64 spin(20);
65 }
66 });
67
68 // wait for thread to start and block
69 started.await();
70 await(thread, Thread.State.BLOCKED);
71 threads.add(thread);
72 }
73
74 // start virtual threads that block on monitorenter while pinned
75 int carriersAvailable = Runtime.getRuntime().availableProcessors();
76 if (Thread.currentThread().isVirtual()) {
77 carriersAvailable--;
78 }
79 for (int i = 0; i < 100; i++) {
80 var started = new CountDownLatch(1);
81 Thread thread = Thread.startVirtualThread(() -> {
82 started.countDown();
83 VThreadPinner.runPinned(() -> {
84 synchronized (lock) {
85 spin(20);
86 }
87 });
88 });
89
90 // if there are carriers available when wait until the thread blocks.
91 if (carriersAvailable > 0) {
92 System.out.printf("%s waiting for thread #%d to block%n",
93 Instant.now(), thread.threadId());
94 started.await();
95 await(thread, Thread.State.BLOCKED);
96 carriersAvailable--;
97 }
98 threads.add(thread);
99 }
100
101 } // exit monitor
102
103 // wait for all threads to terminate
104 int threadsRemaining = threads.size();
105 while (threadsRemaining > 0) {
106 System.out.printf("%s waiting for %d threads to terminate%n",
107 Instant.now(), threadsRemaining);
108 int terminated = 0;
109 for (Thread t : threads) {
110 if (t.join(Duration.ofSeconds(1))) {
111 terminated++;
112 }
113 }
114 threadsRemaining = threads.size() - terminated;
115 }
116 System.out.printf("%s done%n", Instant.now());
117 }
118
119 /**
120 * Spin for the given number of milliseconds.
121 */
122 static void spin(long millis) {
123 long nanos = TimeUnit.MILLISECONDS.toNanos(millis);
124 long start = System.nanoTime();
125 while ((System.nanoTime() - start) < nanos) {
126 Thread.onSpinWait();
127 }
128 }
129
130 /**
131 * Wait for a thread to reach the expected state.
132 */
133 static void await(Thread thread, Thread.State expectedState) throws InterruptedException {
134 Thread.State state = thread.getState();
135 while (state != expectedState) {
136 assert state != Thread.State.TERMINATED : "Thread has terminated";
137 Thread.sleep(10);
138 state = thread.getState();
139 }
140 }
141 }