/*
* 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.cocoon.pipeline;
import java.io.ByteArrayOutputStream;
import org.apache.cocoon.pipeline.caching.CacheKey;
import org.apache.cocoon.pipeline.caching.CacheRefreshJob;
import org.apache.cocoon.pipeline.caching.CacheRefreshManager;
import org.apache.cocoon.pipeline.caching.CacheValue;
import org.apache.cocoon.pipeline.caching.CompleteCacheValue;
import org.apache.cocoon.pipeline.component.PipelineComponent;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* <p>
* This {@link Pipeline} basically works like the {@link CachingPipeline}. The only difference is that when the cached
* result isn't valid anymore, the refresh is done in a separate thread. This means that the re-production of the result
* doesn't block the initial request. The disadvantage of this approach is that until the result is being reproduced, an
* out-dated result is returned. If this is out of question for a use case, the {@link CachingPipeline} has to be used.
* </p>
*/
public class AsyncCachePipeline<T extends PipelineComponent> extends CachingPipeline<T> implements CacheRefreshJob {
private final Log logger = LogFactory.getLog(this.getClass());
/**
* The component that does the refresh in a separate thread.
*/
private CacheRefreshManager cacheRefreshManager;
/**
* {@inheritDoc}
*
* @see org.apache.cocoon.pipeline.CachingPipeline#execute()
*/
@Override
public void execute() throws Exception {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Used cache: " + this.cache);
}
// construct the current cache key
this.cacheKey = this.constructCacheKey();
// check for a cached value first
CacheValue cachedValue = this.getCachedValue(this.cacheKey);
if (cachedValue != null) {
// cached value found -> write it
if (this.logger.isDebugEnabled()) {
this.logger.debug("Write cache value to output stream: " + cachedValue);
}
cachedValue.writeTo(this.cachingOutputStream.getOutputStream());
if (!this.isCacheKeyValid(cachedValue)) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Cached value is not up to date. Delegating to " + this.cacheRefreshManager);
}
// the cached value is not valid -> refresh the value
this.cacheRefreshManager.refreshCacheValue(this.cacheKey, this);
}
// stop here
return;
}
// no cached value (not even an invalid one) was present -> execute the pipeline
this.invokeStarter();
// cache the result
CompleteCacheValue cacheValue = new CompleteCacheValue(this.cachingOutputStream.getContent(), this.cacheKey);
this.setCachedValue(this.cacheKey, cacheValue);
}
public CacheRefreshManager getCacheRefreshManager() {
return this.cacheRefreshManager;
}
/**
* {@inheritDoc}
*
* @see org.apache.cocoon.pipeline.caching.CacheRefreshJob#refresh(org.apache.cocoon.pipeline.caching.CacheKey)
*/
public void refresh(CacheKey cacheKey) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
this.getFinisher().setOutputStream(baos);
// execute the pipeline
this.invokeStarter();
this.setCachedValue(cacheKey, new CompleteCacheValue(baos.toByteArray(), cacheKey));
}
public void setCacheRefreshManager(CacheRefreshManager cacheRefreshManager) {
this.cacheRefreshManager = cacheRefreshManager;
}
}