com.facebook.presto.jdbc.internal.jetty.util.thread.Locker Maven / Gradle / Ivy
//
// ========================================================================
// 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 com.facebook.presto.jdbc.internal.jetty.util.thread;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock;
/**
* This is a lock designed to protect VERY short sections of
* critical code. Threads attempting to take the lock will wait
* until the lock is available, thus it is important that
* the code protected by this lock is extremely simple and non
* blocking.
*
* try(SpinLock.Lock lock = locker.lock())
* {
* // something very quick and non blocking
* }
*
*/
public class Locker
{
private static final boolean SPIN = Boolean.getBoolean(Locker.class.getName() + ".spin");
private final boolean _spin;
private final ReentrantLock _lock = new ReentrantLock();
private final AtomicReference _spinLockState = new AtomicReference<>(null);
private final Lock _unlock = new Lock();
public Locker()
{
this(SPIN);
}
public Locker(boolean spin)
{
this._spin = spin;
}
public Lock lock()
{
if (_spin)
spinLock();
else
concLock();
return _unlock;
}
private void spinLock()
{
Thread current = Thread.currentThread();
while (true)
{
// Using test-and-test-and-set for better performance.
Thread locker = _spinLockState.get();
if (locker != null || !_spinLockState.compareAndSet(null, current))
{
if (locker == current)
throw new IllegalStateException("Locker is not reentrant");
continue;
}
return;
}
}
private void concLock()
{
if (_lock.isHeldByCurrentThread())
throw new IllegalStateException("Locker is not reentrant");
_lock.lock();
}
public boolean isLocked()
{
if (_spin)
return _spinLockState.get() != null;
else
return _lock.isLocked();
}
public class Lock implements AutoCloseable
{
@Override
public void close()
{
if (_spin)
_spinLockState.set(null);
else
_lock.unlock();
}
}
}