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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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package org.apache.solr.util;
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import java.util.concurrent.atomic.AtomicInteger;
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/** Keep track of a reference count on a resource and close it when
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* the count hits zero.
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* By itself, this class could have some race conditions
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* since there is no synchronization between the refcount
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* check and the close. Solr's use in reference counting searchers
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* is safe since the count can only hit zero if it's unregistered (and
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* hence incref() will not be called again on it).
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* @version $Id: RefCounted.java 779125 2009-05-27 11:58:18Z noble $
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public abstract class RefCounted<Type> {
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protected final Type resource;
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protected final AtomicInteger refcount = new AtomicInteger();
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public RefCounted(Type resource) {
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this.resource = resource;
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public int getRefcount() {
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return refcount.get();
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public final RefCounted<Type> incref() {
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refcount.incrementAndGet();
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public final Type get() {
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public void decref() {
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if (refcount.decrementAndGet() == 0) {
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protected abstract void close();