Github user denalex commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq/pull/1379#discussion_r202130797
  
    --- Diff: 
pxf/pxf-service/src/main/java/org/apache/hawq/pxf/service/UGICache.java ---
    @@ -0,0 +1,318 @@
    +package org.apache.hawq.pxf.service;
    +
    +/*
    + * 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.
    + */
    +
    +import java.io.IOException;
    +import java.util.HashMap;
    +import java.util.Map;
    +import java.util.concurrent.ConcurrentHashMap;
    +import java.util.concurrent.DelayQueue;
    +import java.util.concurrent.Delayed;
    +import java.util.concurrent.TimeUnit;
    +import java.util.concurrent.atomic.AtomicInteger;
    +
    +import com.google.common.base.Ticker;
    +import org.apache.commons.logging.Log;
    +import org.apache.commons.logging.LogFactory;
    +import org.apache.hadoop.security.UserGroupInformation;
    +
    +/**
    + * Stores UserGroupInformation instances for each active session. The UGIs 
are cleaned up if they
    + * have not been accessed for 15 minutes.
    + * <p>
    + * The motivation for caching is that destroying UGIs is slow. The 
alternative, creating and
    + * destroying a UGI per-request, is wasteful.
    + */
    +public class UGICache {
    +
    +    private static final Log LOG = LogFactory.getLog(UGICache.class);
    +    private Map<SessionId, Entry> cache = new ConcurrentHashMap<>();
    +    @SuppressWarnings("unchecked")
    +    // There is a separate DelayQueue for each segment (also being used 
for locking)
    +    private final Map<Integer, DelayQueue<Entry>> queueMap = new 
HashMap<>();
    +    private final UGIProvider ugiProvider;
    +    private Ticker ticker;
    +    private final static long UGI_CACHE_EXPIRY = 15 * 60 * 1000L; // 15 
Minutes
    +
    +    /**
    +     * Create a UGICache with the given {@link UGIProvider}. Intended for 
use by tests which need
    +     * to substitute a mock UGIProvider.
    +     */
    +    UGICache(UGIProvider provider, Ticker ticker) {
    +        this.ticker = ticker;
    +        this.ugiProvider = provider;
    +    }
    +
    +    /**
    +     * Create a UGICache. Automatically creates a {@link UGIProvider} that 
this cache will use to
    +     * create and destroy UserGroupInformation instances.
    +     */
    +    public UGICache() {
    +        this(new UGIProvider(), Ticker.systemTicker());
    +    }
    +
    +    /**
    +     * Create new proxy UGI if not found in cache and increment reference 
count
    +     */
    +    public UserGroupInformation getUserGroupInformation(SessionId session) 
throws IOException {
    +        Integer segmentId = session.getSegmentId();
    +        String user = session.getUser();
    +        DelayQueue<Entry> delayQueue = getExpirationQueue(segmentId);
    +        synchronized (delayQueue) {
    +            // Use the opportunity to cleanup any expired entries
    +            cleanup(session);
    +            Entry entry = cache.get(session);
    +            if (entry == null) {
    +                LOG.info(session.toString() + " Creating proxy user = " + 
user);
    +                entry = new Entry(ticker, 
ugiProvider.createProxyUGI(user));
    +                delayQueue.offer(entry);
    +                cache.put(session, entry);
    +            }
    +            entry.acquireReference();
    +            return entry.getUGI();
    +        }
    +    }
    +
    +    /**
    +     * Decrement reference count for the given session's UGI. Resets the 
time at which the UGI will
    +     * expire to 15 minutes in the future.
    +     *
    +     * @param session                  the session for which we want to 
release the UGI.
    +     * @param cleanImmediatelyIfNoRefs if true, destroys the UGI for the 
given session (only if it is
    +     *                                 now unreferenced).
    +     */
    +    public void release(SessionId session, boolean 
cleanImmediatelyIfNoRefs) {
    +
    +        Entry timedProxyUGI = cache.get(session);
    +
    +        if (timedProxyUGI == null) return;
    +
    +        timedProxyUGI.resetTime();
    +        timedProxyUGI.releaseReference();
    +        if (cleanImmediatelyIfNoRefs) {
    +            synchronized (getExpirationQueue(session.getSegmentId())) {
    +                timedProxyUGI.setExpired();
    +                closeUGI(session, timedProxyUGI);
    +            }
    +        }
    +    }
    +
    +    /**
    +     * Get the queue of cache entries associated with a segment, creating 
it if it doesn't
    +     * yet exist. This lets us lazily populate the queueMap.
    +     *
    +     * @param segmentId
    +     * @return the {@link DelayQueue} associated to the segment.
    +     */
    +    private DelayQueue<Entry> getExpirationQueue(Integer segmentId) {
    +        DelayQueue<Entry> queue = queueMap.get(segmentId);
    +        if (queue == null) {
    +            synchronized (queueMap) {
    +                queue = queueMap.get(segmentId);
    +                if (queue == null) {
    +                    queue = new DelayQueue<>();
    +                    queueMap.put(segmentId, queue);
    +                }
    +            }
    +        }
    +        return queue;
    +    }
    +
    +    /**
    +     * Iterate through all the entries in the queue for the given 
session's segment
    +     * and close expired {@link UserGroupInformation}, otherwise it resets
    +     * the timer for every non-expired entry.
    +     *
    +     * @param session
    +     */
    +    private void cleanup(SessionId session) {
    +
    +        Entry ugi;
    +        DelayQueue<Entry> delayQueue = 
getExpirationQueue(session.getSegmentId());
    +        while ((ugi = delayQueue.poll()) != null) {
    +            // Place it back in the queue if still in use and was not 
closed
    +            if (!closeUGI(session, ugi)) {
    +                ugi.resetTime();
    +                delayQueue.offer(ugi);
    +            }
    +            LOG.debug("Delay Queue Size for segment " +
    +                    session.getSegmentId() + " = " + delayQueue.size());
    +        }
    +    }
    +
    +    /**
    +     * This method must be called from a synchronized block for the 
delayQueue for the given
    +     * session.getSegmentId(). When the reference count is 0, the Entry is 
removed from the
    +     * cache where it will then be processed to be destroyed by the 
UGIProvider.
    +     *
    +     * @param session
    +     * @param toDelete
    +     * @return true if the UGI entry was cleaned, false when the UGI entry 
was still in use
    +     * and cleaning up was skipped
    +     */
    +    private boolean closeUGI(SessionId session, Entry toDelete) {
    +        // There is no need to synchronize this method because it should 
be called
    +        // from within a synchronized block
    +        String fsMsg = "FileSystem for proxy user = " + 
toDelete.getUGI().getUserName();
    +        try {
    +            // The UGI object is still being used by another thread
    +            if (toDelete.isInUse()) {
    +                LOG.info(session.toString() + " Skipping close of " + 
fsMsg);
    --- End diff --
    
    dial down to debug


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