--- /dev/null
+//
+// ========================================================================
+// Copyright (c) 1995-2016 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 spin lock 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>
+ * <p>Further analysis however, shows that spin locks behave really
+ * bad under heavy contention and where the number of threads
+ * exceeds the number of cores, which are common scenarios for a
+ * server, so this class was removed from usage, preferring
+ * standard locks instead.</p>
+ * @deprecated Do not use it anymore, prefer normal locks
+ */
+@Deprecated
+public class SpinLock
+{
+ private final AtomicReference<Thread> _lock = new AtomicReference<>(null);
+ private final Lock _unlock = new Lock();
+
+ public Lock lock()
+ {
+ Thread thread = Thread.currentThread();
+ while(true)
+ {
+ if (!_lock.compareAndSet(null,thread))
+ {
+ if (_lock.get()==thread)
+ throw new IllegalStateException("SpinLock is not reentrant");
+ continue;
+ }
+ return _unlock;
+ }
+ }
+
+ public boolean isLocked()
+ {
+ return _lock.get()!=null;
+ }
+
+ public boolean isLockedThread()
+ {
+ return _lock.get()==Thread.currentThread();
+ }
+
+ public class Lock implements AutoCloseable
+ {
+ @Override
+ public void close()
+ {
+ _lock.set(null);
+ }
+ }
+}