001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.util;
019
020import java.util.concurrent.locks.Condition;
021
022/**
023 * Represents an object that you can wait for.
024 */
025public class Waitable<T> {
026  private T val;
027  private final Condition cond;
028
029  public Waitable(Condition cond) {
030    this.val = null;
031    this.cond = cond;
032  }
033
034  public T await() throws InterruptedException {
035    while (this.val == null) {
036      this.cond.await();
037    }
038    return this.val;
039  }
040
041  public void provide(T val) {
042    this.val = val;
043    this.cond.signalAll();
044  }
045
046  public boolean hasVal() {
047    return this.val != null;
048  }
049
050  public T getVal() {
051    return this.val;
052  }
053}