| // |
| // ======================================================================== |
| // Copyright (c) 1995-2015 Mort Bay Consulting Pty. Ltd. |
| // ------------------------------------------------------------------------ |
| // All rights reserved. This program and the accompanying materials |
| // are made available under the terms of the Eclipse Public License v1.0 |
| // and Apache License v2.0 which accompanies this distribution. |
| // |
| // The Eclipse Public License is available at |
| // http://www.eclipse.org/legal/epl-v10.html |
| // |
| // The Apache License v2.0 is available at |
| // http://www.opensource.org/licenses/apache2.0.php |
| // |
| // You may elect to redistribute this code under either of these licenses. |
| // ======================================================================== |
| // |
| |
| package org.eclipse.jetty.util.thread; |
| |
| import java.util.concurrent.atomic.AtomicReference; |
| |
| /** |
| * <p>This is a lock designed to protect VERY short sections of |
| * critical code. Threads attempting to take the lock will spin |
| * forever until the lock is available, thus it is important that |
| * the code protected by this lock is extremely simple and non |
| * blocking. The reason for this lock is that it prevents a thread |
| * from giving up a CPU core when contending for the lock.</p> |
| * <pre> |
| * try(SpinLock.Lock lock = spinlock.lock()) |
| * { |
| * // something very quick and non blocking |
| * } |
| * </pre> |
| */ |
| public class SpinLock |
| { |
| private final AtomicReference<Thread> _lock = new AtomicReference<>(null); |
| private final Lock _unlock = new Lock(); |
| |
| public Lock lock() |
| { |
| Thread current = Thread.currentThread(); |
| while (true) |
| { |
| // Using test-and-test-and-set for better performance. |
| Thread locker = _lock.get(); |
| if (locker != null || !_lock.compareAndSet(null, current)) |
| { |
| if (locker == current) |
| throw new IllegalStateException("SpinLock is not reentrant"); |
| continue; |
| } |
| return _unlock; |
| } |
| } |
| |
| public boolean isLocked() |
| { |
| return _lock.get() != null; |
| } |
| |
| public class Lock implements AutoCloseable |
| { |
| @Override |
| public void close() |
| { |
| _lock.set(null); |
| } |
| } |
| } |