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     */
018    package org.apache.hadoop.util;
019    
020    import java.util.concurrent.locks.Condition;
021    
022    /**
023     * Represents an object that you can wait for.
024     */
025    public 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    }