com.redhat.lightblue.metadata.mongo.MetadataCache.java Source code

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Here is the source code for com.redhat.lightblue.metadata.mongo.MetadataCache.java

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/*
 Copyright 2013 Red Hat, Inc. and/or its affiliates.
    
 This file is part of lightblue.
    
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.
    
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
    
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.redhat.lightblue.metadata.mongo;

import java.util.Map;
import java.util.HashMap;

import java.lang.ref.WeakReference;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.mongodb.DBCollection;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import com.mongodb.WriteResult;

import com.redhat.lightblue.EntityVersion;

import com.redhat.lightblue.metadata.EntityMetadata;

public class MetadataCache {

    private static Logger LOGGER = LoggerFactory.getLogger(MetadataCache.class);

    private static final String LITERAL_COLL_VER = "collectionVersion";

    /**
     * This is the collection version number we expect to see in the
     * database. If this doesn't match the value in db, someone
     * updated metadata, we refresh
     */
    private long expectedCollectionVersion;

    /**
     * Last time we retrieved collection version
     */
    private volatile long lastVersionLookupTime = 0l;

    /**
     * The collection version lookup period
     */
    private long versionLookupPeriodMsecs = 10l * 1000l;

    /**
     * Cache clear period
     */
    private long cacheTTLMsecs = 10l * 60l * 1000l;

    /**
     * Last time we refreshed cache
     */
    private volatile long lastCacheRefreshTime = 0l;

    private final Map<EntityVersion, WeakReference<EntityMetadata>> cache = new HashMap<>();

    /**
     * Sets cache parameters. If null is passed, that parameter is not changed.
     */
    public void setCacheParams(Long versionLookupPeriodMsecs, Long cacheTTLMsecs) {
        if (versionLookupPeriodMsecs != null)
            this.versionLookupPeriodMsecs = versionLookupPeriodMsecs;
        if (cacheTTLMsecs != null)
            this.cacheTTLMsecs = cacheTTLMsecs;
    }

    public EntityMetadata lookup(DBCollection collection, String entityName, String version) {
        long now = System.currentTimeMillis();
        if (lastCacheRefreshTime + cacheTTLMsecs < now)
            fullRefresh(collection, now);
        else if (lastVersionLookupTime + versionLookupPeriodMsecs < now)
            refreshCollectionVersion(collection, now, false);

        EntityMetadata md;
        EntityVersion v = new EntityVersion(entityName, version);
        WeakReference<EntityMetadata> ref = cache.get(v);
        if (ref != null)
            md = ref.get();
        else
            md = null;

        return md;
    }

    public synchronized void put(EntityMetadata md) {
        cache.put(new EntityVersion(md.getName(), md.getVersion().getValue()), new WeakReference(md));
    }

    /**
     * Update the collection version in db, and invalidate cache
     */
    public synchronized void updateCollectionVersion(DBCollection collection) {
        BasicDBObject query = new BasicDBObject(MongoMetadata.LITERAL_ID, LITERAL_COLL_VER);
        BasicDBObject update = new BasicDBObject("$inc", new BasicDBObject(LITERAL_COLL_VER, 1));
        int nUpdated;
        try {
            WriteResult r = collection.update(query, update);
            nUpdated = r.getN();
        } catch (Exception e) {
            nUpdated = 0;
        }
        if (nUpdated == 0) {
            // Try to ins
            BasicDBObject doc = new BasicDBObject(MongoMetadata.LITERAL_ID, LITERAL_COLL_VER);
            doc.put(LITERAL_COLL_VER, 0l);
            try {
                collection.insert(doc);
            } catch (Exception e) {
            }
        }
        cache.clear();
    }

    /**
     * Load the cache version from the db.
     */
    private synchronized Long loadCacheVersion(DBCollection collection) {
        BasicDBObject query = new BasicDBObject("_id", "collectionVersion");
        DBObject obj = collection.findOne(query);
        if (obj == null) {
            updateCollectionVersion(collection);
            obj = collection.findOne(query);
            if (obj == null) {
                // Leave it uninitialized
                LOGGER.error("Cannot initialize metadata cache");
            }
        }
        if (obj != null) {
            return (Long) obj.get("collectionVersion");
        } else {
            return null;
        }
    }

    private synchronized void fullRefresh(DBCollection collection, long now) {
        if (lastCacheRefreshTime + cacheTTLMsecs < now) {
            if (!refreshCollectionVersion(collection, now, true))
                cache.clear();
            lastCacheRefreshTime = now;
        }
    }

    /**
     * Refreshes the collection version. Returns true if the cache is invalidated
     */
    private synchronized boolean refreshCollectionVersion(DBCollection collection, long now,
            boolean bypassRecheck) {
        // Re-check if one of the timers really expired. One of the
        // other threads might have already initialized it
        boolean ret = false;
        if (bypassRecheck || lastVersionLookupTime + versionLookupPeriodMsecs < now) {
            Long v = loadCacheVersion(collection);
            if (v != null) {
                if (v != expectedCollectionVersion) {
                    cache.clear();
                    expectedCollectionVersion = v;
                    ret = true;
                }
                lastVersionLookupTime = now;
            }
        }
        return ret;
    }
}