/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.ode.bpel.runtime;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import org.apache.ode.bpel.runtime.channels.ReadWriteLock;
import org.apache.ode.jacob.JacobRunnable;
import org.apache.ode.jacob.ReceiveProcess;
import org.apache.ode.jacob.Synch;
/**
* A fair READ-WRITE lock.
*
* @author Maciej Szefler <mszefler at gmail dot com>
*
*/
public class READWRITELOCK extends JacobRunnable {
private static final long serialVersionUID = -7415586067226921615L;
private static enum Status {
UNLOCKED, READLOCK, WRITELOCK,
}
private LinkedList<Waiter> _waiters = new LinkedList<Waiter>();
private HashSet<Synch> _owners = new HashSet<Synch>();
private Status _status = Status.UNLOCKED;
private ReadWriteLock _self;
public READWRITELOCK(ReadWriteLock self) {
_self = self;
}
@Override
public void run() {
object(new ReceiveProcess() {
private static final long serialVersionUID = -8644268413754259515L;
}.setChannel(_self).setReceiver(new ReadWriteLock() {
public void readLock(Synch s) {
switch (_status) {
case UNLOCKED:
_status = Status.READLOCK;
_owners.add(s);
s.ret();
break;
case READLOCK:
_owners.add(s);
s.ret();
break;
case WRITELOCK:
_waiters.add(new Waiter(s, false));
break;
}
instance(READWRITELOCK.this);
}
public void writeLock(Synch s) {
switch (_status) {
case UNLOCKED:
_status = Status.WRITELOCK;
_owners.add(s);
s.ret();
break;
case READLOCK:
_waiters.add(new Waiter(s, true));
break;
case WRITELOCK:
_waiters.add(new Waiter(s, false));
break;
}
instance(READWRITELOCK.this);
}
public void unlock(Synch s) {
_owners.remove(s);
if (_owners.isEmpty()) {
_status = Status.UNLOCKED;
if (!_waiters.isEmpty()) {
Waiter w = _waiters.removeFirst();
_owners.add(w.synch);
_status = w.write ? Status.WRITELOCK : Status.READLOCK;
w.synch.ret();
if (_status == Status.READLOCK) {
for (Iterator<Waiter> i = _waiters.iterator(); i.hasNext();) {
Waiter w1 = i.next();
if (w1.write)
break;
_owners.add(w1.synch);
w1.synch.ret();
i.remove();
}
}
}
}
instance(READWRITELOCK.this);
}
}));
}
private static class Waiter {
Synch synch;
boolean write;
Waiter(Synch s, boolean w) {
synch = s;
write = w;
}
}
}