Several fixes to actual, probable and possible synchronocity issues (#691)

* Several fixes to actual, probable and possible synchronocity issues
 - Ensure that all edits are queued onto the same AsyncNotifyQueue by actually delegating to the parent player in PlayerProxy
 - Ensure that the order editsessions are being remembered on the LocalSession is being respected by using a fair ReentrentLock
 - Ensure a chunk cannot be called when an update is being called

* Don't add locks to GetBlocks

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/adapter/mc1_15_2/BukkitGetBlocks_1_15_2_Copy.java

@@ -106,7 +106,7 @@ public class BukkitGetBlocks_1_15_2_Copy extends BukkitGetBlocks_1_15_2 {
     }
 
     protected void storeSection(int layer) {
-        update(layer, blocks[layer]);
+        blocks[layer] = update(layer, null).clone();
     }
 
     @Override

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/adapter/mc1_16_1/BukkitGetBlocks_1_16_1_Copy.java

@@ -107,7 +107,7 @@ public class BukkitGetBlocks_1_16_1_Copy extends BukkitGetBlocks_1_16_1 {
     }
 
     protected void storeSection(int layer) {
-        update(layer, blocks[layer]);
+        blocks[layer] = update(layer, null).clone();
     }
 
     @Override

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/adapter/mc1_16_2/BukkitGetBlocks_1_16_2_Copy.java

@@ -107,7 +107,7 @@ public class BukkitGetBlocks_1_16_2_Copy extends BukkitGetBlocks_1_16_2 {
     }
 
     protected void storeSection(int layer) {
-        update(layer, blocks[layer]);
+        blocks[layer] = update(layer, null).clone();
     }
 
     @Override

worldedit-core/src/main/java/com/sk89q/worldedit/LocalSession.java

@@ -92,9 +92,12 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
+import java.util.Random;
 import java.util.TimeZone;
 import java.util.UUID;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Collectors;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -116,7 +119,7 @@ public class LocalSession implements TextureHolder {
     // Session related
     private transient RegionSelector selector = new CuboidRegionSelector();
     private transient boolean placeAtPos1 = false;
-    private transient List<Object> history = Collections.synchronizedList(new LinkedList<Object>() {
+    private final transient List<Object> history = Collections.synchronizedList(new LinkedList<Object>() {
         @Override
         public Object get(int index) {
             Object value = super.get(index);
@@ -135,6 +138,7 @@ public class LocalSession implements TextureHolder {
     private transient volatile Integer historyNegativeIndex;
     private transient ClipboardHolder clipboard;
     private transient final Object clipboardLock = new Object();
+    private transient final Lock historyWriteLock = new ReentrantLock(true);
     private transient boolean superPickaxe = false;
     private transient BlockTool pickaxeMode = new SinglePickaxe();
     private final transient Int2ObjectOpenHashMap<Tool> tools = new Int2ObjectOpenHashMap<>(0);
@@ -439,7 +443,9 @@ public class LocalSession implements TextureHolder {
         return null;
     }
 
-    public synchronized void remember(Identifiable player, World world, ChangeSet changeSet, FaweLimit limit) {
+    public void remember(Identifiable player, World world, ChangeSet changeSet, FaweLimit limit) {
+        historyWriteLock.lock();
+        try {
             if (Settings.IMP.HISTORY.USE_DISK) {
                 LocalSession.MAX_HISTORY_SIZE = Integer.MAX_VALUE;
             }
@@ -480,9 +486,14 @@ public class LocalSession implements TextureHolder {
                     historySize -= size;
                 }
             }
+        } finally {
+            historyWriteLock.unlock();
+        }
     }
 
-    public synchronized void remember(EditSession editSession, boolean append, int limitMb) {
+    public void remember(EditSession editSession, boolean append, int limitMb) {
+        historyWriteLock.lock();
+        try {
             if (Settings.IMP.HISTORY.USE_DISK) {
                 LocalSession.MAX_HISTORY_SIZE = Integer.MAX_VALUE;
             }
@@ -491,12 +502,6 @@ public class LocalSession implements TextureHolder {
             if (editSession.getChangeSet() == null || limitMb == 0 || historySize >> 20 > limitMb && !append) {
                 return;
             }
-        /*
-        // Don't store anything if no changes were made
-        if (editSession.size() == 0) {
-            return;
-        }
-        */
 
             ChangeSet changeSet = editSession.getChangeSet();
             if (changeSet.isEmpty()) {
@@ -543,6 +548,9 @@ public class LocalSession implements TextureHolder {
                 long size = MainUtil.getSize(item);
                 historySize -= size;
             }
+        } finally {
+            historyWriteLock.unlock();
+        }
     }
 
     /**

worldedit-core/src/main/java/com/sk89q/worldedit/extension/platform/AbstractPlayerActor.java

@@ -684,6 +684,7 @@ public abstract class AbstractPlayerActor implements Actor, Player, Cloneable {
      * @param async TODO description
      * @return false if the task was ran or queued
      */
+    @Override
     public boolean runAction(Runnable ifFree, boolean checkFree, boolean async) {
         if (checkFree) {
             if (runningCount.get() != 0) {

worldedit-core/src/main/java/com/sk89q/worldedit/extension/platform/PlayerProxy.java

@@ -83,6 +83,11 @@ public class PlayerProxy extends AbstractPlayerActor {
         return basePlayer.getBlockInHand(handSide);
     }
 
+    @Override
+    public boolean runAction(Runnable ifFree, boolean checkFree, boolean async) {
+        return basePlayer.runAction(ifFree, checkFree, async);
+    }
+
     @Override
     public UUID getUniqueId() {
         return basePlayer.getUniqueId();