Use a queue rather than a set in TickScheduler

We now track whether a tile is enqueued or not via an atomic boolean on
the block entity itself, rather than using a hash set. This is
significantly faster (>10x).

This is mostly intended for monitors, as they're the only peripheral
likely to call TickScheduler.schedule lots of times (rather than modems,
which just invoke it when opening/closing a channel[^1])[^2]. This
change is enough to allow me to update 120 monitors each tick without
any major tearing.

[^1]: GPS does do this on each gps.locate call, so it will help there,
but modems are typically limited by other computers sending messages,
not peripheral calls themselves.

[^2]: Note that montitors implement their own change tracking, so still
only call this once per tick. But it's enough to introduce some latency!

src/main/java/dan200/computercraft/shared/common/TileGeneric.java

@@ -19,9 +19,17 @@ import net.minecraft.util.math.BlockRayTraceResult;
 import net.minecraftforge.common.util.Constants;
 
 import javax.annotation.Nonnull;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 public abstract class TileGeneric extends TileEntity
 {
+    /**
+     * Is this block enqueued to be updated next tick? This should only be read/written by the tick scheduler.
+     *
+     * @see dan200.computercraft.shared.util.TickScheduler
+     */
+    public final AtomicBoolean scheduled = new AtomicBoolean();
+
     public TileGeneric( TileEntityType<? extends TileGeneric> type )
     {
         super( type );

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

@@ -5,10 +5,8 @@
  */
 package dan200.computercraft.shared.util;
 
-import com.google.common.collect.MapMaker;
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.shared.common.TileGeneric;
-import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.ITickList;
 import net.minecraft.world.World;
@@ -16,9 +14,8 @@ import net.minecraftforge.event.TickEvent;
 import net.minecraftforge.eventbus.api.SubscribeEvent;
 import net.minecraftforge.fml.common.Mod;
 
-import java.util.Collections;
+import java.util.Queue;
-import java.util.Iterator;
+import java.util.concurrent.ConcurrentLinkedDeque;
-import java.util.Set;
 
 /**
  * A thread-safe version of {@link ITickList#scheduleTick(BlockPos, Object, int)}.
@@ -32,16 +29,12 @@ public final class TickScheduler
     {
     }
 
-    private static final Set<TileEntity> toTick = Collections.newSetFromMap(
+    private static final Queue<TileGeneric> toTick = new ConcurrentLinkedDeque<>();
-        new MapMaker()
-            .weakKeys()
-            .makeMap()
-    );
 
     public static void schedule( TileGeneric tile )
     {
         World world = tile.getLevel();
-        if( world != null && !world.isClientSide ) toTick.add( tile );
+        if( world != null && !world.isClientSide && !tile.scheduled.getAndSet( true ) ) toTick.add( tile );
     }
 
     @SubscribeEvent
@@ -49,11 +42,11 @@ public final class TickScheduler
     {
         if( event.phase != TickEvent.Phase.START ) return;
 
-        Iterator<TileEntity> iterator = toTick.iterator();
+        TileGeneric tile;
-        while( iterator.hasNext() )
+        while( (tile = toTick.poll()) != null )
         {
-            TileEntity tile = iterator.next();
+            tile.scheduled.set( false );
-            iterator.remove();
+            if( tile.isRemoved() ) continue;
 
             World world = tile.getLevel();
             BlockPos pos = tile.getBlockPos();