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/*
* Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* @test id=default
* @summary Test virtual threads entering a lot of monitors with contention
* @requires vm.opt.LockingMode != 1
* @library /test/lib
* @run main LotsOfContendedMonitorEnter
*/
/*
* @test id=LM_LIGHTWEIGHT
* @requires vm.opt.LockingMode != 1
* @library /test/lib
* @run main/othervm -XX:LockingMode=2 LotsOfContendedMonitorEnter
*/
import java.util.concurrent.CountDownLatch;
import jdk.test.lib.thread.VThreadRunner;
public class LotsOfContendedMonitorEnter {
public static void main(String[] args) throws Exception {
int depth;
if (args.length > 0) {
depth = Integer.parseInt(args[0]);
} else {
depth = 1024;
}
VThreadRunner.run(() -> testContendedEnter(depth));
}
/**
* Enter the monitor for a new object, racing with another virtual thread that
* attempts to enter around the same time, then repeat to the given depth.
*/
private static void testContendedEnter(int depthRemaining) throws Exception {
if (depthRemaining > 0) {
var lock = new Object();
// start thread to enter monitor for brief period, then enters again when signalled
var started = new CountDownLatch(1);
var signal = new CountDownLatch(1);
var thread = Thread.ofVirtual().start(() -> {
started.countDown();
// enter, may be contended
synchronized (lock) {
Thread.onSpinWait();
}
// wait to be signalled
try {
signal.await();
} catch (InterruptedException e) { }
// enter again, this will block until the main thread releases
synchronized (lock) {
// do nothing
}
});
try {
// wait for thread to start
started.await();
// enter, may be contended
synchronized (lock) {
// signal thread to enter monitor again, it should block
signal.countDown();
await(thread, Thread.State.BLOCKED);
testContendedEnter(depthRemaining - 1);
}
} finally {
thread.join();
}
}
}
/**
* Waits for the given thread to reach a given state.
*/
private static void await(Thread thread, Thread.State expectedState) {
Thread.State state = thread.getState();
while (state != expectedState) {
assert state != Thread.State.TERMINATED : "Thread has terminated";
Thread.yield();
state = thread.getState();
}
}
}
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