Index: src/java/org/apache/lucene/util/cache/ConcurrentLRUCache.java
===================================================================
--- src/java/org/apache/lucene/util/cache/ConcurrentLRUCache.java	(revision 0)
+++ src/java/org/apache/lucene/util/cache/ConcurrentLRUCache.java	(revision 0)
@@ -0,0 +1,391 @@
+package org.apache.lucene.util.cache;
+/**
+ * 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 org.apache.lucene.util.PriorityQueue;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * A LRU cache implementation based upon ConcurrentHashMap and other techniques to reduce
+ * contention and synchronization overhead to utilize multiple CPU cores more effectively.
+ * <p/>
+ * Note that the implementation does not follow a true LRU (least-recently-used) eviction
+ * strategy. Instead it strives to remove least recently used items but when the initial
+ * cleanup does not remove enough items to reach the 'acceptableWaterMark' limit, it can
+ * remove more items forcefully regardless of access order.
+ * <p/>
+ */
+public class ConcurrentLRUCache<K,V> {
+  private final ConcurrentHashMap<Object, CacheEntry> map;
+  private final int upperWaterMark, lowerWaterMark;
+  private final ReentrantLock markAndSweepLock = new ReentrantLock(true);
+  private boolean isCleaning = false;  // not volatile... piggybacked on other volatile vars
+  private final int acceptableWaterMark;
+  private long oldestEntry = 0;  // not volatile, only accessed in the cleaning method
+  private final AtomicInteger size = new AtomicInteger();
+  private final AtomicLong accessCounter = new AtomicLong();
+
+  public ConcurrentLRUCache(int upperWaterMark, final int lowerWaterMark, int acceptableWatermark, int initialSize) {
+    if (upperWaterMark < 1) throw new IllegalArgumentException("upperWaterMark must be > 0");
+    if (lowerWaterMark >= upperWaterMark)
+      throw new IllegalArgumentException("lowerWaterMark must be  < upperWaterMark");
+    map = new ConcurrentHashMap<Object, CacheEntry>(initialSize);
+    this.upperWaterMark = upperWaterMark;
+    this.lowerWaterMark = lowerWaterMark;
+    this.acceptableWaterMark = acceptableWatermark;
+  }
+
+
+  public V get(K key) {
+    CacheEntry<K,V> e = map.get(key);
+    if (e == null) {
+      return null;
+    }
+    e.lastAccessed = accessCounter.incrementAndGet();
+    return e.value;
+  }
+
+  public V remove(K key) {
+    CacheEntry<K,V> cacheEntry = map.remove(key);
+    if (cacheEntry != null) {
+      size.decrementAndGet();
+      return cacheEntry.value;
+    }
+    return null;
+  }
+
+  public Object put(K key, V val) {
+    if (val == null) return null;
+    CacheEntry e = new CacheEntry(key, val, accessCounter.incrementAndGet());
+    CacheEntry oldCacheEntry = map.put(key, e);
+    int currentSize;
+    if (oldCacheEntry == null) {
+      currentSize = size.incrementAndGet();
+    } else {
+      currentSize = size.get();      
+    }
+
+    // Check if we need to clear out old entries from the cache.
+    // isCleaning variable is checked instead of markAndSweepLock.isLocked()
+    // for performance because every put invokation will check until
+    // the size is back to an acceptable level.
+    //
+    // There is a race between the check and the call to markAndSweep, but
+    // it's unimportant because markAndSweep actually aquires the lock or returns if it can't.
+    //
+    // Thread safety note: isCleaning read is piggybacked (comes after) other volatile reads
+    // in this method.
+    if (currentSize > upperWaterMark && !isCleaning) {
+      markAndSweep();
+    }
+    return oldCacheEntry == null ? null : oldCacheEntry.value;
+  }
+
+  /**
+   * Removes items from the cache to bring the size down
+   * to an acceptable value ('acceptableWaterMark').
+   * <p/>
+   * It is done in two stages. In the first stage, least recently used items are evicted.
+   * If, after the first stage, the cache size is still greater than 'acceptableSize'
+   * config parameter, the second stage takes over.
+   * <p/>
+   * The second stage is more intensive and tries to bring down the cache size
+   * to the 'lowerWaterMark' config parameter.
+   */
+  private void markAndSweep() {
+    // if we want to keep at least 1000 entries, then timestamps of
+    // current through current-1000 are guaranteed not to be the oldest (but that does
+    // not mean there are 1000 entries in that group... it's acutally anywhere between
+    // 1 and 1000).
+    // Also, if we want to remove 500 entries, then
+    // oldestEntry through oldestEntry+500 are guaranteed to be
+    // removed (however many there are there).
+
+    if (!markAndSweepLock.tryLock()) return;
+    try {
+      long oldestEntry = this.oldestEntry;
+      isCleaning = true;
+      this.oldestEntry = oldestEntry;     // volatile write to make isCleaning visible
+
+      long timeCurrent = accessCounter.get();
+      int sz = size.get();
+
+      int numRemoved = 0;
+      int numKept = 0;
+      long newestEntry = timeCurrent;
+      long newNewestEntry = -1;
+      long newOldestEntry = Integer.MAX_VALUE;
+
+      int wantToKeep = lowerWaterMark;
+      int wantToRemove = sz - lowerWaterMark;
+
+      CacheEntry<K,V>[] eset = new CacheEntry[sz];
+      int eSize = 0;
+
+      // System.out.println("newestEntry="+newestEntry + " oldestEntry="+oldestEntry);
+      // System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
+
+      for (CacheEntry<K,V> ce : map.values()) {
+        // set lastAccessedCopy to avoid more volatile reads
+        ce.lastAccessedCopy = ce.lastAccessed;
+        long thisEntry = ce.lastAccessedCopy;
+
+        // since the wantToKeep group is likely to be bigger than wantToRemove, check it first
+        if (thisEntry > newestEntry - wantToKeep) {
+          // this entry is guaranteed not to be in the bottom
+          // group, so do nothing.
+          numKept++;
+          newOldestEntry = Math.min(thisEntry, newOldestEntry);
+        } else if (thisEntry < oldestEntry + wantToRemove) { // entry in bottom group?
+          // this entry is guaranteed to be in the bottom group
+          // so immediately remove it from the map.
+          evictEntry(ce.key);
+          numRemoved++;
+        } else {
+          // This entry *could* be in the bottom group.
+          // Collect these entries to avoid another full pass... this is wasted
+          // effort if enough entries are normally removed in this first pass.
+          // An alternate impl could make a full second pass.
+          if (eSize < eset.length-1) {
+            eset[eSize++] = ce;
+            newNewestEntry = Math.max(thisEntry, newNewestEntry);
+            newOldestEntry = Math.min(thisEntry, newOldestEntry);
+          }
+        }
+      }
+
+      // System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
+      // TODO: allow this to be customized in the constructor?
+      int numPasses=1; // maximum number of linear passes over the data
+
+      // if we didn't remove enough entries, then make more passes
+      // over the values we collected, with updated min and max values.
+      while (sz - numRemoved > acceptableWaterMark && --numPasses>=0) {
+
+        oldestEntry = newOldestEntry == Integer.MAX_VALUE ? oldestEntry : newOldestEntry;
+        newOldestEntry = Integer.MAX_VALUE;
+        newestEntry = newNewestEntry;
+        newNewestEntry = -1;
+        wantToKeep = lowerWaterMark - numKept;
+        wantToRemove = sz - lowerWaterMark - numRemoved;
+
+        // iterate backward to make it easy to remove items.
+        for (int i=eSize-1; i>=0; i--) {
+          CacheEntry<K,V> ce = eset[i];
+          long thisEntry = ce.lastAccessedCopy;
+
+          if (thisEntry > newestEntry - wantToKeep) {
+            // this entry is guaranteed not to be in the bottom
+            // group, so do nothing but remove it from the eset.
+            numKept++;
+            // remove the entry by moving the last element to it's position
+            eset[i] = eset[eSize-1];
+            eSize--;
+
+            newOldestEntry = Math.min(thisEntry, newOldestEntry);
+
+          } else if (thisEntry < oldestEntry + wantToRemove) { // entry in bottom group?
+
+            // this entry is guaranteed to be in the bottom group
+            // so immediately remove it from the map.
+            evictEntry(ce.key);
+            numRemoved++;
+
+            // remove the entry by moving the last element to it's position
+            eset[i] = eset[eSize-1];
+            eSize--;
+          } else {
+            // This entry *could* be in the bottom group, so keep it in the eset,
+            // and update the stats.
+            newNewestEntry = Math.max(thisEntry, newNewestEntry);
+            newOldestEntry = Math.min(thisEntry, newOldestEntry);
+          }
+        }
+        // System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " esetSz="+ eSize + " sz-numRemoved=" + (sz-numRemoved));
+      }
+
+
+
+      // if we still didn't remove enough entries, then make another pass while
+      // inserting into a priority queue
+      if (sz - numRemoved > acceptableWaterMark) {
+
+        oldestEntry = newOldestEntry == Integer.MAX_VALUE ? oldestEntry : newOldestEntry;
+        newOldestEntry = Integer.MAX_VALUE;
+        newestEntry = newNewestEntry;
+        newNewestEntry = -1;
+        wantToKeep = lowerWaterMark - numKept;
+        wantToRemove = sz - lowerWaterMark - numRemoved;
+
+        PQueue queue = new PQueue(wantToRemove);
+
+        for (int i=eSize-1; i>=0; i--) {
+          CacheEntry<K,V> ce = eset[i];
+          long thisEntry = ce.lastAccessedCopy;
+
+          if (thisEntry > newestEntry - wantToKeep) {
+            // this entry is guaranteed not to be in the bottom
+            // group, so do nothing but remove it from the eset.
+            numKept++;
+            // removal not necessary on last pass.
+            // eset[i] = eset[eSize-1];
+            // eSize--;
+
+            newOldestEntry = Math.min(thisEntry, newOldestEntry);
+
+          } else if (thisEntry < oldestEntry + wantToRemove) {  // entry in bottom group?
+            // this entry is guaranteed to be in the bottom group
+            // so immediately remove it.
+            evictEntry(ce.key);
+            numRemoved++;
+
+            // removal not necessary on last pass.
+            // eset[i] = eset[eSize-1];
+            // eSize--;
+          } else {
+            // This entry *could* be in the bottom group.
+            // add it to the priority queue
+
+            // everything in the priority queue will be removed, so keep track of
+            // the lowest value that ever comes back out of the queue.
+
+            // first reduce the size of the priority queue to account for
+            // the number of items we have already removed while executing
+            // this loop so far.
+            queue.myMaxSize = sz - lowerWaterMark - numRemoved;
+            while (queue.size() > queue.myMaxSize && queue.size() > 0) {
+              CacheEntry otherEntry = (CacheEntry) queue.pop();
+              newOldestEntry = Math.min(otherEntry.lastAccessedCopy, newOldestEntry);
+            }
+            if (queue.myMaxSize <= 0) break;
+
+            Object o = queue.myInsertWithOverflow(ce);
+            if (o != null) {
+              newOldestEntry = Math.min(((CacheEntry)o).lastAccessedCopy, newOldestEntry);
+            }
+          }
+        }
+
+        // Now delete everything in the priority queue.
+        // avoid using pop() since order doesn't matter anymore
+        for (Object o : queue.getValues()) {
+          if (o==null) continue;
+          CacheEntry<K,V> ce = (CacheEntry)o;
+          evictEntry(ce.key);
+          numRemoved++;
+        }
+
+        // System.out.println("items removed:" + numRemoved + " numKept=" + numKept + " initialQueueSize="+ wantToRemove + " finalQueueSize=" + queue.size() + " sz-numRemoved=" + (sz-numRemoved));
+      }
+
+      oldestEntry = newOldestEntry == Integer.MAX_VALUE ? oldestEntry : newOldestEntry;
+      this.oldestEntry = oldestEntry;
+    } finally {
+      isCleaning = false;  // set before markAndSweep.unlock() for visibility
+      markAndSweepLock.unlock();
+    }
+  }
+
+  private static class PQueue extends PriorityQueue {
+    int myMaxSize;
+    PQueue(int maxSz) {
+      super.initialize(maxSz);
+      myMaxSize = maxSz;
+    }
+
+    Object[] getValues() { return heap; }
+
+    protected boolean lessThan(Object a, Object b) {
+      // reverse the parameter order so that the queue keeps the oldest items
+      return ((CacheEntry)b).lastAccessedCopy < ((CacheEntry)a).lastAccessedCopy;
+    }
+
+    // necessary because maxSize is private in base class
+    public Object myInsertWithOverflow(Object element) {
+      if (size() < myMaxSize) {
+        add(element);
+        return null;
+      } else if (size() > 0 && !lessThan(element, heap[1])) {
+        Object ret = heap[1];
+        heap[1] = element;
+        updateTop();
+        return ret;
+      } else {
+        return element;
+      }
+    }
+  }
+
+
+  private void evictEntry(K key) {
+    CacheEntry<K,V> o = map.remove(key);
+    if (o == null) return;
+    size.decrementAndGet();
+  }
+
+  public int size() {
+    return size.get();
+  }
+
+  public void clear() {
+    map.clear();
+  }
+
+  public Map<Object, CacheEntry> getMap() {
+    return map;
+  }
+
+  private static class CacheEntry<K,V> implements Comparable<CacheEntry> {
+    K key;
+    V value;
+    volatile long lastAccessed = 0;
+    long lastAccessedCopy = 0;
+
+
+    public CacheEntry(K key, V value, long lastAccessed) {
+      this.key = key;
+      this.value = value;
+      this.lastAccessed = lastAccessed;
+    }
+
+    public void setLastAccessed(long lastAccessed) {
+      this.lastAccessed = lastAccessed;
+    }
+
+    public int compareTo(CacheEntry that) {
+      if (this.lastAccessedCopy == that.lastAccessedCopy) return 0;
+      return this.lastAccessedCopy < that.lastAccessedCopy ? 1 : -1;
+    }
+
+    public int hashCode() {
+      return value.hashCode();
+    }
+
+    public boolean equals(Object obj) {
+      return value.equals(obj);
+    }
+
+    public String toString() {
+      return "key: " + key + " value: " + value + " lastAccessed:" + lastAccessed;
+    }
+  }
+}
\ No newline at end of file

Property changes on: src/java/org/apache/lucene/util/cache/ConcurrentLRUCache.java
___________________________________________________________________
Added: svn:executable
   + *
Added: svn:keywords
   + Date Author Id Revision HeadURL
Added: svn:eol-style
   + native