Begin investigations into reducing ticking of TEs

- Move IDirectionalTile constraint from IPeripheralTile to
   TilePeripheralBase.
 - Make *WiredModemFull no longer inherit from *PeripheralBase. While
   there is still some shared logic (namely in the syncing of "anim"),
   it's largely fine as we don't store label or direction in NBT.
 - Add a TickScheduler. This is a thread-safe version of
   World.scheduleUpdate. We simply build a set of all TEs, and schedule
   them to be updated the next tick.
 - Make ModemState receive an "onChanged" listener, which is fired
   whenever the modem changes.
 - Make WiredModemFull no longer tick, instead scheduling updates when
   it is first loaded and whenever the modem changes.

src/main/java/dan200/computercraft/shared/computer/blocks/BlockCommandComputer.java

@@ -8,19 +8,15 @@ package dan200.computercraft.shared.computer.blocks;
 
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
-import dan200.computercraft.shared.util.DirectionUtil;
 import net.minecraft.block.material.Material;
 import net.minecraft.block.properties.PropertyDirection;
 import net.minecraft.block.properties.PropertyEnum;
 import net.minecraft.block.state.BlockStateContainer;
 import net.minecraft.block.state.IBlockState;
-import net.minecraft.entity.EntityLivingBase;
-import net.minecraft.item.ItemStack;
 import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.EnumFacing;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockAccess;
-import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 

src/main/java/dan200/computercraft/shared/peripheral/common/IPeripheralTile.java

@@ -7,15 +7,17 @@
 package dan200.computercraft.shared.peripheral.common;
 
 import dan200.computercraft.api.peripheral.IPeripheral;
-import dan200.computercraft.shared.common.IDirectionalTile;
 import dan200.computercraft.shared.peripheral.PeripheralType;
 import net.minecraft.util.EnumFacing;
 
-public interface IPeripheralTile extends IDirectionalTile
+public interface IPeripheralTile
 {
     PeripheralType getPeripheralType();
 
     IPeripheral getPeripheral( EnumFacing side );
 
-    String getLabel();
+    default String getLabel()
+    {
+        return null;
+    }
 }

src/main/java/dan200/computercraft/shared/peripheral/common/TilePeripheralBase.java

@@ -7,6 +7,7 @@
 package dan200.computercraft.shared.peripheral.common;
 
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.shared.common.IDirectionalTile;
 import dan200.computercraft.shared.common.TileGeneric;
 import dan200.computercraft.shared.peripheral.PeripheralType;
 import net.minecraft.item.ItemStack;
@@ -17,8 +18,7 @@ import net.minecraft.util.NonNullList;
 
 import javax.annotation.Nonnull;
 
-public abstract class TilePeripheralBase extends TileGeneric
-    implements IPeripheralTile, ITickable
+public abstract class TilePeripheralBase extends TileGeneric implements IPeripheralTile, ITickable, IDirectionalTile
 {
     // Statics
 

src/main/java/dan200/computercraft/shared/peripheral/modem/ModemState.java

@@ -14,16 +14,27 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
 public class ModemState
 {
-    private boolean open = false;
-    private AtomicBoolean changed = new AtomicBoolean( true );
+    private final Runnable onChanged;
+    private final AtomicBoolean changed = new AtomicBoolean( true );
 
+    private boolean open = false;
     private final IntSet channels = new IntOpenHashSet();
 
+    public ModemState()
+    {
+        this.onChanged = null;
+    }
+
+    public ModemState( Runnable onChanged )
+    {
+        this.onChanged = onChanged;
+    }
+
     private void setOpen( boolean open )
     {
         if( this.open == open ) return;
         this.open = open;
-        this.changed.set( true );
+        if( !changed.getAndSet( true ) && onChanged != null ) onChanged.run();
     }
 
     public boolean pollChanged()

src/main/java/dan200/computercraft/shared/peripheral/modem/wired/BlockWiredModemFull.java

@@ -7,20 +7,21 @@
 package dan200.computercraft.shared.peripheral.modem.wired;
 
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.shared.peripheral.PeripheralType;
-import dan200.computercraft.shared.peripheral.common.BlockPeripheralBase;
-import dan200.computercraft.shared.peripheral.common.TilePeripheralBase;
+import dan200.computercraft.shared.common.BlockGeneric;
+import dan200.computercraft.shared.common.TileGeneric;
+import net.minecraft.block.material.Material;
 import net.minecraft.block.properties.PropertyBool;
 import net.minecraft.block.state.BlockStateContainer;
 import net.minecraft.block.state.IBlockState;
 import net.minecraft.tileentity.TileEntity;
-import net.minecraft.util.EnumFacing;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockAccess;
+import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
+import java.util.Random;
 
-public class BlockWiredModemFull extends BlockPeripheralBase
+public class BlockWiredModemFull extends BlockGeneric
 {
     // Statics
 
@@ -34,6 +35,7 @@ public class BlockWiredModemFull extends BlockPeripheralBase
 
     public BlockWiredModemFull()
     {
+        super( Material.ROCK );
         setHardness( 1.5f );
         setTranslationKey( "computercraft:wired_modem_full" );
         setCreativeTab( ComputerCraft.mainCreativeTab );
@@ -43,12 +45,6 @@ public class BlockWiredModemFull extends BlockPeripheralBase
         );
     }
 
-    @Override
-    protected IBlockState getDefaultBlockState( PeripheralType type, EnumFacing placedSide )
-    {
-        return getDefaultState();
-    }
-
     @Nonnull
     @Override
     protected BlockStateContainer createBlockState()
@@ -74,7 +70,7 @@ public class BlockWiredModemFull extends BlockPeripheralBase
         if( te instanceof TileWiredModemFull )
         {
             TileWiredModemFull modem = (TileWiredModemFull) te;
-            int anim = modem.getAnim();
+            int anim = modem.getState();
             state = state
                 .withProperty( Properties.MODEM_ON, (anim & 1) != 0 )
                 .withProperty( Properties.PERIPHERAL_ON, (anim & 2) != 0 );
@@ -84,19 +80,20 @@ public class BlockWiredModemFull extends BlockPeripheralBase
     }
 
     @Override
-    public PeripheralType getPeripheralType( int damage )
+    public void updateTick( World world, BlockPos pos, IBlockState state, Random rand )
     {
-        return PeripheralType.WiredModemFull;
+        TileEntity te = world.getTileEntity( pos );
+        if( te instanceof TileWiredModemFull ) ((TileWiredModemFull) te).updateTick();
     }
 
     @Override
-    public PeripheralType getPeripheralType( IBlockState state )
+    protected TileGeneric createTile( IBlockState state )
     {
-        return PeripheralType.WiredModemFull;
+        return new TileWiredModemFull();
     }
 
     @Override
-    public TilePeripheralBase createTile( PeripheralType type )
+    protected TileGeneric createTile( int damage )
     {
         return new TileWiredModemFull();
     }

src/main/java/dan200/computercraft/shared/peripheral/modem/wired/TileWiredModemFull.java

@@ -12,8 +12,11 @@ import dan200.computercraft.api.network.wired.IWiredElement;
 import dan200.computercraft.api.network.wired.IWiredNode;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.shared.command.CommandCopy;
-import dan200.computercraft.shared.peripheral.common.TilePeripheralBase;
+import dan200.computercraft.shared.common.TileGeneric;
+import dan200.computercraft.shared.peripheral.PeripheralType;
+import dan200.computercraft.shared.peripheral.common.IPeripheralTile;
 import dan200.computercraft.shared.peripheral.modem.ModemState;
+import dan200.computercraft.shared.util.TickScheduler;
 import dan200.computercraft.shared.wired.CapabilityWiredElement;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.nbt.NBTTagCompound;
@@ -30,7 +33,7 @@ import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.*;
 
-public class TileWiredModemFull extends TilePeripheralBase
+public class TileWiredModemFull extends TileGeneric implements IPeripheralTile
 {
     private static class FullElement extends WiredModemElement
     {
@@ -85,10 +88,12 @@ public class TileWiredModemFull extends TilePeripheralBase
     private boolean m_destroyed = false;
     private boolean m_connectionsFormed = false;
 
-    private final ModemState m_modemState = new ModemState();
+    private final ModemState m_modemState = new ModemState( () -> TickScheduler.schedule( this ) );
     private final WiredModemElement m_element = new FullElement( this );
     private final IWiredNode m_node = m_element.getNode();
 
+    private int m_state = 0;
+
     public TileWiredModemFull()
     {
         for( int i = 0; i < m_peripherals.length; i++ ) m_peripherals[i] = new WiredModemLocalPeripheral();
@@ -128,17 +133,6 @@ public class TileWiredModemFull extends TilePeripheralBase
         remove();
     }
 
-    @Override
-    public EnumFacing getDirection()
-    {
-        return EnumFacing.NORTH;
-    }
-
-    @Override
-    public void setDirection( EnumFacing dir )
-    {
-    }
-
     @Override
     public void onNeighbourChange()
     {
@@ -231,27 +225,50 @@ public class TileWiredModemFull extends TilePeripheralBase
         return nbt;
     }
 
-    protected void updateAnim()
+    public int getState()
     {
-        int anim = 0;
-        if( m_modemState.isOpen() ) anim |= 1;
-        if( m_peripheralAccessAllowed ) anim |= 2;
-        setAnim( anim );
+        return m_state;
+    }
+
+    private void updateState()
+    {
+        int state = 0;
+        if( m_modemState.isOpen() ) state |= 1;
+        if( m_peripheralAccessAllowed ) state |= 2;
+        if( state != m_state )
+        {
+            m_state = state;
+            updateBlock();
+        }
+    }
+
+    @Override
+    protected void writeDescription( @Nonnull NBTTagCompound nbt )
+    {
+        super.writeDescription( nbt );
+        nbt.setInteger( "state", m_state );
     }
 
     @Override
     public final void readDescription( @Nonnull NBTTagCompound nbt )
     {
         super.readDescription( nbt );
+        m_state = nbt.getInteger( "state" );
         updateBlock();
     }
 
     @Override
-    public void update()
+    public void onLoad()
+    {
+        super.onLoad();
+        if( !world.isRemote ) world.scheduleUpdate( pos, getBlockType(), 0 );
+    }
+
+    protected void updateTick()
     {
         if( !getWorld().isRemote )
         {
-            if( m_modemState.pollChanged() ) updateAnim();
+            if( m_modemState.pollChanged() ) updateState();
 
             if( !m_connectionsFormed )
             {
@@ -268,8 +285,6 @@ public class TileWiredModemFull extends TilePeripheralBase
                 }
             }
         }
-
-        super.update();
     }
 
     private void connectionsChanged()
@@ -291,7 +306,6 @@ public class TileWiredModemFull extends TilePeripheralBase
         }
     }
 
-    // private stuff
     private void togglePeripheralAccess()
     {
         if( !m_peripheralAccessAllowed )
@@ -317,7 +331,7 @@ public class TileWiredModemFull extends TilePeripheralBase
             m_node.updatePeripherals( Collections.emptyMap() );
         }
 
-        updateAnim();
+        updateState();
     }
 
     private Set<String> getConnectedPeripheralNames()
@@ -349,7 +363,7 @@ public class TileWiredModemFull extends TilePeripheralBase
         {
             // If there are no peripherals then disable access and update the display state.
             m_peripheralAccessAllowed = false;
-            updateAnim();
+            updateState();
         }
 
         m_node.updatePeripherals( peripherals );
@@ -360,7 +374,8 @@ public class TileWiredModemFull extends TilePeripheralBase
     @Override
     public boolean hasCapability( @Nonnull Capability<?> capability, @Nullable EnumFacing facing )
     {
-        return capability == CapabilityWiredElement.CAPABILITY || super.hasCapability( capability, facing );
+        if( capability == CapabilityWiredElement.CAPABILITY ) return !m_destroyed;
+        return super.hasCapability( capability, facing );
     }
 
     @Nullable
@@ -369,6 +384,7 @@ public class TileWiredModemFull extends TilePeripheralBase
     {
         if( capability == CapabilityWiredElement.CAPABILITY )
         {
+            if( m_destroyed ) return null;
             return CapabilityWiredElement.CAPABILITY.cast( m_element );
         }
 
@@ -377,9 +393,17 @@ public class TileWiredModemFull extends TilePeripheralBase
 
     // IPeripheralTile
 
+    @Override
+    public PeripheralType getPeripheralType()
+    {
+        return PeripheralType.WiredModemFull;
+    }
+
     @Override
     public IPeripheral getPeripheral( EnumFacing side )
     {
+        if( m_destroyed ) return null;
+
         WiredModemPeripheral peripheral = m_modems[side.ordinal()];
         if( peripheral == null )
         {

src/main/java/dan200/computercraft/shared/util/TickScheduler.java

@@ -0,0 +1,68 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.shared.util;
+
+import com.google.common.collect.MapMaker;
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.shared.common.TileGeneric;
+import net.minecraft.block.Block;
+import net.minecraft.tileentity.TileEntity;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
+import net.minecraftforge.fml.common.gameevent.TickEvent;
+
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.Set;
+
+/**
+ * A thread-safe version of {@link World#scheduleUpdate(BlockPos, Block, int)}.
+ *
+ * We use this when modems and other peripherals change a block in a different thread.
+ */
+@Mod.EventBusSubscriber( modid = ComputerCraft.MOD_ID )
+public final class TickScheduler
+{
+    private TickScheduler()
+    {
+    }
+
+    private static final Set<TileEntity> toTick = Collections.newSetFromMap(
+        new MapMaker()
+            .weakKeys()
+            .makeMap()
+    );
+
+    public static void schedule( TileGeneric tile )
+    {
+        World world = tile.getWorld();
+        if( world != null && !world.isRemote ) toTick.add( tile );
+    }
+
+    @SubscribeEvent
+    public static void tick( TickEvent.ServerTickEvent event )
+    {
+        if( event.phase != TickEvent.Phase.START ) return;
+
+        Iterator<TileEntity> iterator = toTick.iterator();
+        while( iterator.hasNext() )
+        {
+            TileEntity tile = iterator.next();
+            iterator.remove();
+
+            World world = tile.getWorld();
+            BlockPos pos = tile.getPos();
+
+            if( world != null && pos != null && world.isBlockLoaded( pos ) && world.getTileEntity( pos ) == tile )
+            {
+                world.scheduleUpdate( pos, tile.getBlockType(), 0 );
+            }
+        }
+    }
+}