/*
* JBoss, Home of Professional Open Source.
* Copyright 2000 - 2008, Red Hat Middleware LLC, and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.cache.util.concurrent.locks;
import net.jcip.annotations.ThreadSafe;
import org.jboss.cache.invocation.InvocationContextContainer;
import org.jboss.cache.transaction.GlobalTransaction;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Lock;
/**
* A lock that supports reentrancy based on owner (and not on current thread). For this to work, the lock needs to be
* constructed with a reference to the {@link org.jboss.cache.invocation.InvocationContextContainer}, so it is able
* to determine whether the caller's "owner" reference is the current thread or a {@link org.jboss.cache.transaction.GlobalTransaction}
* instance.
* <p/>
* This makes this lock implementation very closely tied to JBoss Cache internals, but it provides for a very clean, efficient
* and moreover familiar interface to work with, since it implements {@link java.util.concurrent.locks.Lock}.
* <p/>
* For the sake of performance, this lock only supports nonfair queueing.
* <p/>
*
* @author Manik Surtani (<a href="mailto:manik AT jboss DOT org">manik AT jboss DOT org</a>)
* @since 3.0
*/
@ThreadSafe
public class OwnableReentrantLock extends AbstractQueuedSynchronizer implements Lock
{
/**
* Current owner
*/
transient Object owner;
/**
* Invocation context to consult when testing the current requestor
*/
transient InvocationContextContainer invocationContextContainer;
/**
* Creates a new lock instance.
*
* @param invocationContextContainer InvocationContextContainer instance to consult for the invocation context of the call.
*/
public OwnableReentrantLock(InvocationContextContainer invocationContextContainer)
{
if (invocationContextContainer == null)
throw new IllegalArgumentException("Invocation context container cannot be null!");
this.invocationContextContainer = invocationContextContainer;
}
/**
* @return a GlobalTransaction instance if the current call is participating in a transaction, or the current thread otherwise.
*/
protected final Object currentRequestor()
{
GlobalTransaction gtx;
return (gtx = invocationContextContainer.get().getGlobalTransaction()) == null ? Thread.currentThread() : gtx;
}
public void lock()
{
if (compareAndSetState(0, 1))
owner = currentRequestor();
else
acquire(1);
}
public void lockInterruptibly() throws InterruptedException
{
acquireInterruptibly(1);
}
public boolean tryLock()
{
return tryAcquire(1);
}
public boolean tryLock(long time, TimeUnit unit) throws InterruptedException
{
return tryAcquireNanos(1, unit.toNanos(time));
}
public void unlock()
{
release(1);
}
public ConditionObject newCondition()
{
throw new UnsupportedOperationException("Not supported in this implementation!");
}
@Override
protected final boolean tryAcquire(int acquires)
{
final Object current = currentRequestor();
int c = getState();
if (c == 0)
{
if (compareAndSetState(0, acquires))
{
owner = current;
return true;
}
}
else if (current.equals(owner))
{
setState(c + acquires);
return true;
}
return false;
}
@Override
protected final boolean tryRelease(int releases)
{
int c = getState() - releases;
if (!currentRequestor().equals(owner))
throw new IllegalMonitorStateException(this.toString());
boolean free = false;
if (c == 0)
{
free = true;
owner = null;
}
setState(c);
return free;
}
@Override
protected final boolean isHeldExclusively()
{
return getState() != 0 && currentRequestor().equals(owner);
}
/**
* @return the owner of the lock, or null if it is currently unlocked.
*/
public final Object getOwner()
{
int c = getState();
Object o = owner;
return (c == 0) ? null : o;
}
/**
* @return the hold count of the current lock, or 0 if it is not locked.
*/
public final int getHoldCount()
{
int c = getState();
Object o = owner;
return (currentRequestor().equals(o)) ? c : 0;
}
/**
* @return true if the lock is locked, false otherwise
*/
public final boolean isLocked()
{
return getState() != 0;
}
/**
* Reconstitute this lock instance from a stream, resetting the lock to an unlocked state.
*
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException
{
s.defaultReadObject();
setState(0); // reset to unlocked state
}
/**
* Returns a string identifying this lock, as well as its lock
* state. The state, in brackets, includes either the String
* "Unlocked" or the String "Locked by"
* followed by the String representation of the lock owner.
*
* @return a string identifying this lock, as well as its lock state.
*/
public String toString()
{
Object owner = getOwner();
return super.toString() + ((owner == null) ?
"[Unlocked]" :
"[Locked by " + owner + "]");
}
}