| /** |
| * 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.hadoop.util; |
| |
| import java.util.concurrent.locks.Lock; |
| import java.util.concurrent.locks.Condition; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| |
| /** |
| * This is a wrap class of a ReentrantLock. Extending AutoCloseable |
| * interface such that the users can use a try-with-resource syntax. |
| */ |
| public class AutoCloseableLock implements AutoCloseable { |
| |
| private final Lock lock; |
| |
| /** |
| * Creates an instance of {@code AutoCloseableLock}, initializes |
| * the underlying lock instance with a new {@code ReentrantLock}. |
| */ |
| public AutoCloseableLock() { |
| this(new ReentrantLock()); |
| } |
| |
| /** |
| * Wrap provided Lock instance. |
| * @param lock Lock instance to wrap in AutoCloseable API. |
| */ |
| public AutoCloseableLock(Lock lock) { |
| this.lock = lock; |
| } |
| |
| /** |
| * A wrapper method that makes a call to {@code lock()} of the underlying |
| * {@code ReentrantLock} object. |
| * |
| * Acquire teh lock it is not held by another thread, then sets |
| * lock held count to one, then returns immediately. |
| * |
| * If the current thread already holds the lock, increase the lock |
| * help count by one and returns immediately. |
| * |
| * If the lock is held by another thread, the current thread is |
| * suspended until the lock has been acquired by current thread. |
| * |
| * @return The {@code ReentrantLock} object itself. This is to |
| * support try-with-resource syntax. |
| */ |
| public AutoCloseableLock acquire() { |
| lock.lock(); |
| return this; |
| } |
| |
| /** |
| * A wrapper method that makes a call to {@code unlock()} of the |
| * underlying {@code ReentrantLock} object. |
| * |
| * Attempts to release the lock. |
| * |
| * If the current thread holds the lock, decrements the hold |
| * count. If the hold count reaches zero, the lock is released. |
| * |
| * If the current thread does not hold the lock, then |
| * {@link IllegalMonitorStateException} is thrown. |
| */ |
| public void release() { |
| lock.unlock(); |
| } |
| |
| /** |
| * Attempts to release the lock by making a call to {@code release()}. |
| * |
| * This is to implement {@code close()} method from {@code AutoCloseable} |
| * interface. This allows users to user a try-with-resource syntax, where |
| * the lock can be automatically released. |
| */ |
| @Override |
| public void close() { |
| release(); |
| } |
| |
| /** |
| * A wrapper method that makes a call to {@code tryLock()} of |
| * the underlying {@code Lock} object. |
| * |
| * If the lock is not held by another thread, acquires the lock, set the |
| * hold count to one and returns {@code true}. |
| * |
| * If the current thread already holds the lock, the increment the hold |
| * count by one and returns {@code true}. |
| * |
| * If the lock is held by another thread then the method returns |
| * immediately with {@code false}. |
| * |
| * @return {@code true} if the lock was free and was acquired by the |
| * current thread, or the lock was already held by the current |
| * thread; and {@code false} otherwise. |
| */ |
| public boolean tryLock() { |
| return lock.tryLock(); |
| } |
| |
| /** |
| * A wrapper method that makes a call to {@code isLocked()} of |
| * the underlying {@code ReentrantLock} object. |
| * |
| * Queries if this lock is held by any thread. This method is |
| * designed for use in monitoring of the system state, |
| * not for synchronization control. |
| * |
| * @return {@code true} if any thread holds this lock and |
| * {@code false} otherwise |
| */ |
| @VisibleForTesting |
| boolean isLocked() { |
| if (lock instanceof ReentrantLock) { |
| return ((ReentrantLock)lock).isLocked(); |
| } |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * See {@link ReentrantLock#newCondition()}. |
| * @return the Condition object |
| */ |
| public Condition newCondition() { |
| return lock.newCondition(); |
| } |
| } |