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[STORE] Add simple cache for StoreStats
this commit tries to reduce the filesystem calls to fetch metadata by using a simple cache on top of the stats call. Relates to elastic#9683 Closes elastic#9709
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src/main/java/org/elasticsearch/common/util/SingleObjectCache.java
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/* | ||
* Licensed to Elasticsearch under one or more contributor | ||
* license agreements. See the NOTICE file distributed with | ||
* this work for additional information regarding copyright | ||
* ownership. Elasticsearch 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.elasticsearch.common.util; | ||
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import org.elasticsearch.common.unit.TimeValue; | ||
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import java.util.concurrent.locks.Lock; | ||
import java.util.concurrent.locks.ReentrantLock; | ||
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/** | ||
* A very simple single object cache that allows non-blocking refresh calls | ||
* triggered by expiry time. | ||
*/ | ||
public abstract class SingleObjectCache<T> { | ||
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private volatile T cached; | ||
private Lock refreshLock = new ReentrantLock(); | ||
private final TimeValue refreshInterval; | ||
protected long lastRefreshTimestamp = 0; | ||
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protected SingleObjectCache(TimeValue refreshInterval, T initialValue) { | ||
if (initialValue == null) { | ||
throw new IllegalArgumentException("initialValue must not be null"); | ||
} | ||
this.refreshInterval = refreshInterval; | ||
cached = initialValue; | ||
} | ||
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/** | ||
* Returns the currently cached object and potentially refreshes the cache before returning. | ||
*/ | ||
public T getOrRefresh() { | ||
if (needsRefresh()) { | ||
if (refreshLock.tryLock()) { | ||
try { | ||
if (needsRefresh()) { // check again! | ||
cached = refresh(); | ||
assert cached != null; | ||
lastRefreshTimestamp = System.currentTimeMillis(); | ||
} | ||
} finally { | ||
refreshLock.unlock(); | ||
} | ||
} | ||
} | ||
assert cached != null; | ||
return cached; | ||
} | ||
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/** | ||
* Returns a new instance to cache | ||
*/ | ||
protected abstract T refresh(); | ||
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/** | ||
* Returns <code>true</code> iff the cache needs to be refreshed. | ||
*/ | ||
protected boolean needsRefresh() { | ||
if (refreshInterval.millis() == 0) { | ||
return true; | ||
} | ||
final long currentTime = System.currentTimeMillis(); | ||
return (currentTime - lastRefreshTimestamp) > refreshInterval.millis(); | ||
} | ||
} |
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