Updated SoftMap to be concurrent.

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

@@ -13,11 +13,11 @@ 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.SoftMap;
+import org.bukkit.craftbukkit.util.ConcurrentSoftMap;
 
 public class CraftChunk implements Chunk {
     private WeakReference<net.minecraft.server.Chunk> weakChunk;
-    private final SoftMap<Integer, Block> cache = new SoftMap<Integer, Block>();
+    private final ConcurrentSoftMap<Integer, Block> cache = new ConcurrentSoftMap<Integer, Block>();
     private WorldServer worldServer;
     private int x;
     private int z;
@@ -63,8 +63,13 @@ public class CraftChunk implements Chunk {
         int pos = (x & 0xF) << 11 | (z & 0xF) << 7 | (y & 0x7F);
         Block block = this.cache.get( pos );
         if (block == null) {
-            block = new CraftBlock( this, (getX() << 4) | (x & 0xF), y & 0x7F, (getZ() << 4) | (z & 0xF) );
-            this.cache.put( pos, block );
+            Block newBlock = new CraftBlock( this, (getX() << 4) | (x & 0xF), y & 0x7F, (getZ() << 4) | (z & 0xF) );
+            Block oldBlock = this.cache.put( pos, newBlock );
+            if(oldBlock == null) {
+                block = newBlock;
+            } else {
+                block = oldBlock;
+            } 
         }
         return block;
     }

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

@@ -3,7 +3,7 @@ package org.bukkit.craftbukkit.util;
 import java.util.Map;
 import java.util.AbstractMap;
 import java.util.LinkedList;
-import java.util.HashMap;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.Set;
 import java.util.Collection;
 import java.util.Iterator;
@@ -13,52 +13,54 @@ 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 
+ * that they can be removed if necessary
  *
- * A minimum number of strong references can be set.  These most recent N objects added 
+ * 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 
+ *       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 SoftMap<K,V> {
+public class ConcurrentSoftMap<K,V> {
 
-    private final HashMap<K,SoftMapReference<K,V>> map = new HashMap<K,SoftMapReference<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 SoftMap() {
+    public ConcurrentSoftMap() {
         this(20);
     }
 
-    public SoftMap(int size) {
+    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 HashMap as keys.  This method removes these keys.
-    // 
+    // 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) {
+        while ((ref=(SoftMapReference) queue.poll()) != null) {
             map.remove(ref.key);
         }
     }
 
     public void clear() {
-         strongReferenceQueue.clear();
+         synchronized(strongReferenceQueue) {
+             strongReferenceQueue.clear();
+         }
          map.clear();
          emptyQueue();
     }
@@ -105,9 +107,11 @@ public class SoftMap<K,V> {
         }
         V value = ref.get();
         if (value!=null) {
-            strongReferenceQueue.addFirst(value);
-            if (strongReferenceQueue.size() > strongReferenceSize) {
-                strongReferenceQueue.removeLast();
+            synchronized(strongReferenceQueue) {
+                strongReferenceQueue.addFirst(value);
+                if (strongReferenceQueue.size() > strongReferenceSize) {
+                    strongReferenceQueue.removeLast();
+                }
             }
         }
         return value;
@@ -125,7 +129,7 @@ public class SoftMap<K,V> {
     public boolean isEmpty() {
         emptyQueue();
         return map.isEmpty();
-    } 
+    }
 
     // Return all the keys, again could go out of date
 
@@ -138,27 +142,76 @@ public class SoftMap<K,V> {
 
     public V put(K key, V value) {
         emptyQueue();
-        V old = fastGet(key); 
+        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));
-        strongReferenceQueue.addFirst(value);
-        if (strongReferenceQueue.size() > strongReferenceSize) {
-            strongReferenceQueue.removeLast();
+        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()) {
+        while (itr.hasNext()) {
             K key = itr.next();
-            fastPut(key, (V)other.get(key));
+            fastPut(key, (V) other.get(key));
         }
     }
 
@@ -178,7 +231,7 @@ public class SoftMap<K,V> {
     public int size() {
         emptyQueue();
         return map.size();
-    } 
+    }
 
     // Shouldn't support this since it would create strong references to all the entries
 
@@ -195,6 +248,17 @@ public class SoftMap<K,V> {
             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();
+        }
+    }
 }