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 id=default 26 * @summary Test virtual thread entering (and reentering) a lot of monitors with no contention 27 * @library /test/lib 28 * @run main/othervm LotsOfUncontendedMonitorEnter 29 */ 30 31 /* 32 * @test id=LM_LEGACY 33 * @library /test/lib 34 * @run main/othervm -XX:LockingMode=1 LotsOfUncontendedMonitorEnter 35 */ 36 37 /* 38 * @test id=LM_LIGHTWEIGHT 39 * @library /test/lib 40 * @run main/othervm -XX:LockingMode=2 LotsOfUncontendedMonitorEnter 41 */ 42 43 import java.util.ArrayList; 44 import java.util.List; 45 import java.util.concurrent.ThreadLocalRandom; 46 import jdk.test.lib.thread.VThreadRunner; 47 48 public class LotsOfUncontendedMonitorEnter { 49 50 public static void main(String[] args) throws Exception { 51 int depth; 52 if (args.length > 0) { 53 depth = Integer.parseInt(args[0]); 54 } else { 55 depth = 24; // 33554430 enters 56 } 57 VThreadRunner.run(() -> { 58 testEnter(List.of(), depth); 59 }); 60 } 61 62 /** 63 * Enter the monitor for a new object, reenter a monitor that is already held, and 64 * repeat to the given depth. 65 */ 66 private static void testEnter(List<Object> ownedMonitors, int depthRemaining) { 67 if (depthRemaining > 0) { 68 var lock = new Object(); 69 synchronized (lock) { 70 // new list of owned monitors 71 var monitors = concat(ownedMonitors, lock); 72 testEnter(monitors, depthRemaining - 1); 73 74 // reenter a monitor that is already owned 75 int index = ThreadLocalRandom.current().nextInt(monitors.size()); 76 var otherLock = monitors.get(index); 77 78 synchronized (otherLock) { 79 testEnter(monitors, depthRemaining - 1); 80 } 81 } 82 } 83 } 84 85 /** 86 * Adds an element to a list, returning a new list. 87 */ 88 private static <T> List<T> concat(List<T> list, T object) { 89 var newList = new ArrayList<>(list); 90 newList.add(object); 91 return newList; 92 } 93 }