org.eclipse.jetty.util.thread.SpinLock Maven / Gradle / Ivy
//
// ========================================================================
// Copyright (c) 1995-2018 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.
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//
package org.eclipse.jetty.util.thread;
import java.util.concurrent.atomic.AtomicReference;
/**
* 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.
*
* try(SpinLock.Lock lock = spinlock.lock())
* {
* // something very quick and non blocking
* }
*
* 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.
* @deprecated Do not use it anymore, prefer normal locks
*/
@Deprecated
public class SpinLock
{
private final AtomicReference _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);
}
}
}