hadoop ResourcePool 源码
haddop ResourcePool 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/ResourcePool.java
/*
* 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.fs.impl.prefetch;
import java.io.Closeable;
/**
* Manages a fixed pool of resources.
*
* Avoids creating a new resource if a previously created instance is already available.
*/
public abstract class ResourcePool<T> implements Closeable {
/**
* Acquires a resource blocking if necessary until one becomes available.
*
* @return the acquired resource instance.
*/
public abstract T acquire();
/**
* Acquires a resource blocking if one is immediately available. Otherwise returns null.
* @return the acquired resource instance (if immediately available) or null.
*/
public abstract T tryAcquire();
/**
* Releases a previously acquired resource.
*
* @param item the resource to release.
*/
public abstract void release(T item);
@Override
public void close() {
}
/**
* Derived classes may implement a way to cleanup each item.
*
* @param item the resource to close.
*/
protected void close(T item) {
// Do nothing in this class. Allow overriding classes to take any cleanup action.
}
/**
* Derived classes must implement a way to create an instance of a resource.
*
* @return the created instance.
*/
protected abstract T createNew();
}
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