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KeyedLock.java
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KeyedLock.java
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/*
* Licensed to ElasticSearch and Shay Banon under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. ElasticSearch 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.elasticsearch.common.util.concurrent;
import org.elasticsearch.ElasticSearchIllegalStateException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
/**
* This class manages locks. Locks can be accessed with an identifier and are
* created the first time they are acquired and removed if no thread hold the
* lock. The latter is important to assure that the list of locks does not grow
* infinitely.
*
* A Thread can acquire a lock only once.
*
* */
public class KeyedLock<T> {
private final ConcurrentMap<T, KeyLock> map = new ConcurrentHashMap<T, KeyLock>();
private final ThreadLocal<KeyLock> threadLocal = new ThreadLocal<KeyedLock.KeyLock>();
public void acquire(T key) {
while (true) {
if (threadLocal.get() != null) {
// if we are here, the thread already has the lock
throw new ElasticSearchIllegalStateException("Lock already accquired in Thread" + Thread.currentThread().getId()
+ " for key " + key);
}
KeyLock perNodeLock = map.get(key);
if (perNodeLock == null) {
KeyLock newLock = new KeyLock();
perNodeLock = map.putIfAbsent(key, newLock);
if (perNodeLock == null) {
newLock.lock();
threadLocal.set(newLock);
return;
}
}
assert perNodeLock != null;
int i = perNodeLock.count.get();
if (i > 0 && perNodeLock.count.compareAndSet(i, i + 1)) {
perNodeLock.lock();
threadLocal.set(perNodeLock);
return;
}
}
}
public void release(T key) {
KeyLock lock = threadLocal.get();
if (lock == null) {
throw new ElasticSearchIllegalStateException("Lock not accquired");
}
assert lock.isHeldByCurrentThread();
assert lock == map.get(key);
lock.unlock();
threadLocal.set(null);
int decrementAndGet = lock.count.decrementAndGet();
if (decrementAndGet == 0) {
map.remove(key, lock);
}
}
@SuppressWarnings("serial")
private final static class KeyLock extends ReentrantLock {
private final AtomicInteger count = new AtomicInteger(1);
}
public boolean hasLockedKeys() {
return !map.isEmpty();
}
}