/****************************************************************
* 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.james.util;
import java.util.Hashtable;
/**
* Provides Lock functionality
*
*/
public class Lock {
/**
* An internal hash table of keys to locks
*/
private Hashtable locks = new Hashtable();
/**
* Check to see if the object is locked
*
* @param key the Object on which to check the lock
* @return true if the object is locked, false otherwise
*/
public boolean isLocked(final Object key) {
return (locks.get(key) != null);
}
/**
* Check to see if we can lock on a given object.
*
* @param key the Object on which to lock
* @return true if the calling thread can lock, false otherwise
*/
public boolean canI(final Object key) {
Object o = locks.get( key );
if (null == o || o == this.getCallerId()) {
return true;
}
return false;
}
/**
* Lock on a given object.
*
* @param key the Object on which to lock
* @return true if the locking was successful, false otherwise
*/
public boolean lock(final Object key) {
Object theLock;
synchronized(this) {
theLock = locks.get(key);
if (null == theLock) {
locks.put(key, getCallerId());
return true;
} else if (getCallerId() == theLock) {
return true;
} else {
return false;
}
}
}
/**
* Release the lock on a given object.
*
* @param key the Object on which the lock is held
* @return true if the unlocking was successful, false otherwise
*/
public boolean unlock(final Object key) {
Object theLock;
synchronized (this) {
theLock = locks.get(key);
if (null == theLock) {
return true;
} else if (getCallerId() == theLock) {
locks.remove(key);
return true;
} else {
return false;
}
}
}
/**
* Private helper method to abstract away caller ID.
*
* @return the id of the caller (i.e. the Thread reference)
*/
private Object getCallerId() {
return Thread.currentThread();
}
}
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