1 files changed, 22 insertions, 1 deletions
diff --git a/src/main/java/gregtech/api/threads/GT_Runnable_MachineBlockUpdate.java b/src/main/java/gregtech/api/threads/GT_Runnable_MachineBlockUpdate.java
index 8f7a84e2cb..494b21de1f 100644
--- a/src/main/java/gregtech/api/threads/GT_Runnable_MachineBlockUpdate.java
+++ b/src/main/java/gregtech/api/threads/GT_Runnable_MachineBlockUpdate.java
@@ -1,5 +1,8 @@
 package gregtech.api.threads;
 
+
+import cpw.mods.fml.common.eventhandler.SubscribeEvent;
+import cpw.mods.fml.common.gameevent.TickEvent;
 import gregtech.GT_Mod;
 import gregtech.api.GregTech_API;
 import gregtech.api.interfaces.tileentity.IMachineBlockUpdateable;
@@ -15,6 +18,7 @@ import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
 
 public class GT_Runnable_MachineBlockUpdate implements Runnable {
     // used by runner thread
@@ -23,6 +27,9 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
     private final Set<ChunkCoordinates> visited = new HashSet<>(80);
     private final Queue<ChunkCoordinates> tQueue = new LinkedList<>();
     
+    // Locking
+    private static ReentrantLock lock = new ReentrantLock();
+    
     // Threading
     private static final ThreadFactory THREAD_FACTORY = r -> {
         Thread thread = new Thread(r);
@@ -40,6 +47,15 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
         
     }
 
+    @SubscribeEvent
+    public void onServerTick(TickEvent.ServerTickEvent aEvent) {
+        if (aEvent.phase == TickEvent.Phase.START) {
+            lock.lock();
+        } else {
+            lock.unlock();
+        }
+    }
+
     public static boolean isEnabled() {
         return isEnabled;
     }
@@ -101,8 +117,13 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
         try {
             while (!tQueue.isEmpty()) {
                 final ChunkCoordinates aCoords = tQueue.poll();
+                
+                // This might load a chunk... which might load a TileEntity... which might get added to `loadedTileEntityList`... which might be in the process
+                // of being iterated over during `UpdateEntities()`... which might cause a ConcurrentModificationException.  So, lock that shit.
+                lock.lock();
                 TileEntity tTileEntity = world.getTileEntity(aCoords.posX, aCoords.posY, aCoords.posZ);
-
+                lock.unlock();
+                
                 // See if the block itself needs an update
                 if (tTileEntity instanceof IMachineBlockUpdateable)
                     ((IMachineBlockUpdateable) tTileEntity).onMachineBlockUpdate();