Fixed huge memory leak (gigabytes/hour!) by placing a bukkit under the ceiling.

pom.xml

@@ -79,6 +79,11 @@
       <type>jar</type>
       <scope>provided</scope>
     </dependency>
+    <dependency>
+      <groupId>com.google.guava</groupId>
+      <artifactId>guava-collections</artifactId>
+      <version>r03</version>
+    </dependency>
   </dependencies>
   <!-- This builds a completely 'ready to start' jar with all dependencies inside -->
   <build>

src/main/java/org/bukkit/craftbukkit/CraftChunk.java

@@ -1,6 +1,8 @@
 package org.bukkit.craftbukkit;
 
+import com.google.common.collect.MapMaker;
 import java.lang.ref.WeakReference;
+import java.util.concurrent.ConcurrentMap;
 import net.minecraft.server.ChunkPosition;
 
 import net.minecraft.server.WorldServer;
@@ -11,14 +13,13 @@ import org.bukkit.block.Block;
 import org.bukkit.block.BlockState;
 import org.bukkit.craftbukkit.block.CraftBlock;
 import org.bukkit.entity.Entity;
-import org.bukkit.craftbukkit.util.ConcurrentSoftMap;
 import org.bukkit.ChunkSnapshot;
 import net.minecraft.server.BiomeBase;
 import net.minecraft.server.WorldChunkManager;
 
 public class CraftChunk implements Chunk {
     private WeakReference<net.minecraft.server.Chunk> weakChunk;
-    private final ConcurrentSoftMap<Integer, Block> cache = new ConcurrentSoftMap<Integer, Block>();
+    private final ConcurrentMap<Integer, Block> cache = new MapMaker().softKeys().softValues().makeMap();
     private WorldServer worldServer;
     private int x;
     private int z;

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -1,11 +1,12 @@
 package org.bukkit.craftbukkit;
 
+import com.google.common.collect.MapMaker;
 import org.bukkit.craftbukkit.entity.*;
 import org.bukkit.entity.*;
 import org.bukkit.entity.Entity;
 
 import java.util.ArrayList;
-import java.util.HashMap;
+import java.util.concurrent.ConcurrentMap;
 import java.util.List;
 import java.util.Random;
 import java.util.UUID;
@@ -37,7 +38,7 @@ public class CraftWorld implements World {
     private final WorldServer world;
     private Environment environment;
     private final CraftServer server = (CraftServer)Bukkit.getServer();
-    private HashMap<Integer, CraftChunk> unloadedChunks = new HashMap<Integer, CraftChunk>();
+    private ConcurrentMap<Integer, CraftChunk> unloadedChunks = new MapMaker().weakKeys().weakValues().makeMap();
     private final ChunkGenerator generator;
     private final List<BlockPopulator> populators = new ArrayList<BlockPopulator>();
 

src/main/java/org/bukkit/craftbukkit/util/ConcurrentSoftMap.java

@@ -1,268 +0,0 @@
-package org.bukkit.craftbukkit.util;
-
-import java.util.Map;
-import java.util.LinkedList;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.Set;
-import java.util.Collection;
-import java.util.Iterator;
-
-import java.lang.ref.ReferenceQueue;
-import java.lang.ref.SoftReference;
-
-/**
- * Creates a map that uses soft reference.  This indicates to the garbage collector
- * that they can be removed if necessary
- *
- * A minimum number of strong references can be set.  These most recent N objects added
- * to the map will not be removed by the garbage collector.
- *
- * Objects will never be removed if they are referenced strongly from somewhere else
-
- * Note: While data corruption won't happen, the garbage collector is potentially async
- *       This could lead to the return values from containsKey() and similar methods being
- *       out of date by the time they are used.  The class could return null when the object
- *       is retrieved by a .get() call directly after a .containsKey() call returned true
- *
- * @author raphfrk
- */
-
-public class ConcurrentSoftMap<K, V> {
-
-    private final ConcurrentHashMap<K, SoftMapReference<K, V>> map = new ConcurrentHashMap<K, SoftMapReference<K, V>>();
-    private final ReferenceQueue<SoftMapReference> queue = new ReferenceQueue<SoftMapReference>();
-    private final LinkedList<V> strongReferenceQueue = new LinkedList<V>();
-    private final int strongReferenceSize;
-
-    public ConcurrentSoftMap() {
-        this(20);
-    }
-
-    public ConcurrentSoftMap(int size) {
-        strongReferenceSize = size;
-    }
-
-    // When a soft reference is deleted by the garbage collector, it is set to reference null
-    // and added to the queue
-    //
-    // However, these null references still exist in the ConcurrentHashMap as keys.  This method removes these keys.
-    //
-    // It is called whenever there is a method call of the map.
-
-    private void emptyQueue() {
-        SoftMapReference ref;
-
-        while ((ref = (SoftMapReference) queue.poll()) != null) {
-            map.remove(ref.key);
-        }
-    }
-
-    public void clear() {
-        synchronized (strongReferenceQueue) {
-            strongReferenceQueue.clear();
-        }
-        map.clear();
-        emptyQueue();
-    }
-
-    // Shouldn't support this, since the garbage collection is async
-
-    public boolean containsKey(K key) {
-        emptyQueue();
-        return map.containsKey(key);
-    }
-
-    // Shouldn't support this, since the garbage collection is async
-
-    public boolean containsValue(V value) {
-        emptyQueue();
-        return map.containsValue(value);
-    }
-
-    // Shouldn't support this since it would create strong references to all the entries
-
-    public Set entrySet() {
-        emptyQueue();
-        throw new UnsupportedOperationException("SoftMap does not support this operation, since it creates potentially stong references");
-    }
-
-    // Doesn't support these either
-
-    public boolean equals(Object o) {
-        emptyQueue();
-        throw new UnsupportedOperationException("SoftMap doesn't support equals checks");
-    }
-
-    // This operation returns null if the entry is not in the map
-
-    public V get(K key) {
-        emptyQueue();
-        return fastGet(key);
-    }
-
-    private V fastGet(K key) {
-        SoftMapReference<K, V> ref = map.get(key);
-
-        if (ref == null) {
-            return null;
-        }
-        V value = ref.get();
-
-        if (value != null) {
-            synchronized (strongReferenceQueue) {
-                strongReferenceQueue.addFirst(value);
-                if (strongReferenceQueue.size() > strongReferenceSize) {
-                    strongReferenceQueue.removeLast();
-                }
-            }
-        }
-        return value;
-    }
-
-    // Doesn't support this either
-
-    public int hashCode() {
-        emptyQueue();
-        throw new UnsupportedOperationException("SoftMap doesn't support hashCode");
-    }
-
-    // This is another risky method, since again, garbage collection is async
-
-    public boolean isEmpty() {
-        emptyQueue();
-        return map.isEmpty();
-    }
-
-    // Return all the keys, again could go out of date
-
-    public Set keySet() {
-        emptyQueue();
-        return map.keySet();
-    }
-
-    // Adds the mapping to the map
-
-    public V put(K key, V value) {
-        emptyQueue();
-        V old = fastGet(key);
-        fastPut(key, value);
-        return old;
-    }
-
-    private void fastPut(K key, V value) {
-        map.put(key, new SoftMapReference<K, V>(key, value, queue));
-        synchronized (strongReferenceQueue) {
-            strongReferenceQueue.addFirst(value);
-            if (strongReferenceQueue.size() > strongReferenceSize) {
-                strongReferenceQueue.removeLast();
-            }
-        }
-    }
-
-    public V putIfAbsent(K key, V value) {
-        emptyQueue();
-        return fastPutIfAbsent(key, value);
-    }
-
-    private V fastPutIfAbsent(K key, V value) {
-        V ret = null;
-
-        if (map.containsKey(key)) {
-            SoftMapReference<K, V> current = map.get(key);
-
-            if (current != null) {
-                ret = current.get();
-            }
-        }
-
-        if (ret == null) {
-            SoftMapReference<K, V> newValue = new SoftMapReference<K, V>(key, value, queue);
-            boolean success = false;
-
-            while (!success) {
-                SoftMapReference<K, V> oldValue = map.putIfAbsent(key, newValue);
-
-                if (oldValue == null) { // put was successful (key didn't exist)
-                    ret = null;
-                    success = true;
-                } else {
-                    ret = oldValue.get();
-                    if (ret == null) { // key existed, but referenced null
-                        success = map.replace(key, oldValue, newValue); // try to swap old for new
-                    } else { // key existed, and referenced a valid object
-                        success = true;
-                    }
-                }
-            }
-        }
-
-        if (ret == null) {
-            synchronized (strongReferenceQueue) {
-                strongReferenceQueue.addFirst(value);
-                if (strongReferenceQueue.size() > strongReferenceSize) {
-                    strongReferenceQueue.removeLast();
-                }
-            }
-        }
-
-        return ret;
-    }
-
-    // Adds the mappings to the map
-
-    public void putAll(Map other) {
-        emptyQueue();
-        Iterator<K> itr = other.keySet().iterator();
-        while (itr.hasNext()) {
-            K key = itr.next();
-            fastPut(key, (V) other.get(key));
-        }
-    }
-
-    // Remove object
-
-    public V remove(K key) {
-        emptyQueue();
-        SoftMapReference<K, V> ref = map.remove(key);
-
-        if (ref != null) {
-            return ref.get();
-        }
-        return null;
-    }
-
-    // Returns size, could go out of date
-
-    public int size() {
-        emptyQueue();
-        return map.size();
-    }
-
-    // Shouldn't support this since it would create strong references to all the entries
-
-    public Collection values() {
-        emptyQueue();
-        throw new UnsupportedOperationException("SoftMap does not support this operation, since it creates potentially stong references");
-    }
-
-    private static class SoftMapReference<K, V> extends SoftReference<V> {
-        K key;
-
-        SoftMapReference(K key, V value, ReferenceQueue queue) {
-            super(value, queue);
-            this.key = key;
-        }
-
-        @Override
-        public boolean equals(Object o) {
-            if (o == null) {
-                return false;
-            }
-            if (!(o instanceof SoftMapReference)) {
-                return false;
-            }
-            SoftMapReference other = (SoftMapReference) o;
-            return other.get() == get();
-        }
-    }
-}