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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
* @summary Test that a virtual thread waiting to enter a monitor, while pinning its
* carrier, will retry until it enters the monitor. This avoids starvation when the
* monitor is exited, an unmounted thread is the chosen successor, and the successor
* can't continue because there are no carriers available.
* @modules java.base/java.lang:+open
* @library /test/lib
* @requires vm.opt.LockingMode != 1
* @run main/othervm --enable-native-access=ALL-UNNAMED RetryMonitorEnterWhenPinned
*/
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import jdk.test.lib.thread.VThreadPinner;
public class RetryMonitorEnterWhenPinned {
public static void main(String[] args) throws Exception {
int iterations = (args.length > 0) ? Integer.parseInt(args[0]) : 10;
for (int i = 1; i <= iterations; i++) {
System.out.printf("%s -- iteration %d --%n", Instant.now(), i);
run();
System.out.println();
}
}
static void run() throws Exception {
var threads = new ArrayList<Thread>();
Object lock = new Object();
synchronized (lock) {
// start virtual threads that block on monitorenter
for (int i = 0; i < 100; i++) {
var started = new CountDownLatch(1);
Thread thread = Thread.startVirtualThread(() -> {
started.countDown();
synchronized (lock) {
spin(20);
}
});
// wait for thread to start and block
started.await();
await(thread, Thread.State.BLOCKED);
threads.add(thread);
}
// start virtual threads that block on monitorenter while pinned
int carriersAvailable = Runtime.getRuntime().availableProcessors();
if (Thread.currentThread().isVirtual()) {
carriersAvailable--;
}
for (int i = 0; i < 100; i++) {
var started = new CountDownLatch(1);
Thread thread = Thread.startVirtualThread(() -> {
started.countDown();
VThreadPinner.runPinned(() -> {
synchronized (lock) {
spin(20);
}
});
});
// if there are carriers available when wait until the thread blocks.
if (carriersAvailable > 0) {
System.out.printf("%s waiting for thread #%d to block%n",
Instant.now(), thread.threadId());
started.await();
await(thread, Thread.State.BLOCKED);
carriersAvailable--;
}
threads.add(thread);
}
} // exit monitor
// wait for all threads to terminate
int threadsRemaining = threads.size();
while (threadsRemaining > 0) {
System.out.printf("%s waiting for %d threads to terminate%n",
Instant.now(), threadsRemaining);
int terminated = 0;
for (Thread t : threads) {
if (t.join(Duration.ofSeconds(1))) {
terminated++;
}
}
threadsRemaining = threads.size() - terminated;
}
System.out.printf("%s done%n", Instant.now());
}
/**
* Spin for the given number of milliseconds.
*/
static void spin(long millis) {
long nanos = TimeUnit.MILLISECONDS.toNanos(millis);
long start = System.nanoTime();
while ((System.nanoTime() - start) < nanos) {
Thread.onSpinWait();
}
}
/**
* Wait for a thread to reach the expected state.
*/
static void await(Thread thread, Thread.State expectedState) throws InterruptedException {
Thread.State state = thread.getState();
while (state != expectedState) {
assert state != Thread.State.TERMINATED : "Thread has terminated";
Thread.sleep(10);
state = thread.getState();
}
}
}
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