Merge pull request #414 from GTNewHorizons/maybe_fix_cme_in_machine_update_thread

Do some locking around getTileEntity to avoid CMEs on the main thread

1 files changed, 31 insertions, 3 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..6564cf316a 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 +47,16 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
         
     }
 
+    @SubscribeEvent
+    public void onServerTick(TickEvent.ServerTickEvent aEvent) {
+        // Using onServerTick because there's race conditions in updateTrackedEntities() which is called AFTER the END phase of onWorldTick 
+        if (aEvent.phase == TickEvent.Phase.START) {
+            lock.lock();
+        } else {
+            lock.unlock();
+        }
+    }
+
     public static boolean isEnabled() {
         return isEnabled;
     }
@@ -101,8 +118,19 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
         try {
             while (!tQueue.isEmpty()) {
                 final ChunkCoordinates aCoords = tQueue.poll();
-                TileEntity tTileEntity = world.getTileEntity(aCoords.posX, aCoords.posY, aCoords.posZ);
-
+                final TileEntity tTileEntity;
+                final boolean isMachineBlock;
+                
+                // 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();
+                try {
+                    tTileEntity = world.getTileEntity(aCoords.posX, aCoords.posY, aCoords.posZ);
+                    isMachineBlock = GregTech_API.isMachineBlock(world.getBlock(aCoords.posX, aCoords.posY, aCoords.posZ), world.getBlockMetadata(aCoords.posX, aCoords.posY, aCoords.posZ));
+                } finally {
+                    lock.unlock();
+                }
+                
                 // See if the block itself needs an update
                 if (tTileEntity instanceof IMachineBlockUpdateable)
                     ((IMachineBlockUpdateable) tTileEntity).onMachineBlockUpdate();
@@ -113,7 +141,7 @@ public class GT_Runnable_MachineBlockUpdate implements Runnable {
                 // 3) If the block at the coordinates is marked as a machine block
                 if (visited.size() < 5 
                     || (tTileEntity instanceof IMachineBlockUpdateable && ((IMachineBlockUpdateable) tTileEntity).isMachineBlockUpdateRecursive()) 
-                    || GregTech_API.isMachineBlock(world.getBlock(aCoords.posX, aCoords.posY, aCoords.posZ), world.getBlockMetadata(aCoords.posX, aCoords.posY, aCoords.posZ))) 
+                    || isMachineBlock) 
                 {
                     ChunkCoordinates tCoords;