Tighten logic for handling target tick times in tick scheduler (#4010)

No longer rely on world time as plugins like to screw it up.

Add a new flag -Dpaper.ticklist-max-tick-delay= that
will automatically drop any tick entries that have a delay
exceeding the specified amount. This is only useful
for cleaning up a world that has been corrupted by
certain blocks having a huge tick delay.

Aimed at resolving #3251

Also fix an issue with some rails connecting incorrectly
that I found when testing.

Co-authored-by: Spottedleaf <[email protected]>

2 files changed, 139 insertions, 8 deletions

diff --git a/Spigot-Server-Patches/0427-Optimise-TickListServer-by-rewriting-it.patch b/Spigot-Server-Patches/0427-Optimise-TickListServer-by-rewriting-it.patch
index 58b47c3276..12fce4d284 100644
--- a/Spigot-Server-Patches/0427-Optimise-TickListServer-by-rewriting-it.patch
+++ b/Spigot-Server-Patches/0427-Optimise-TickListServer-by-rewriting-it.patch
@@ -61,10 +61,10 @@ index bf86444c479f346e7d56f10a7c0ebefd62f08f59..8508b3e10e60a4ce36d471b1d3f7ffc8
          ConfigurationSection section;
 diff --git a/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a0e7a7689
+index 0000000000000000000000000000000000000000..bbb042fec32ce5a4aecf1934ab6bed77c5134a7f
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
-@@ -0,0 +1,617 @@
+@@ -0,0 +1,624 @@
 +package com.destroystokyo.paper.server.ticklist;
 +
 +import net.minecraft.server.MCUtil;
@@ -72,7 +72,6 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
 +import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
 +import it.unimi.dsi.fastutil.objects.ObjectRBTreeSet;
-+import net.minecraft.server.BaseBlockPosition;
 +import net.minecraft.server.BlockPosition;
 +import net.minecraft.server.ChunkCoordIntPair;
 +import net.minecraft.server.ChunkProviderServer;
@@ -96,7 +95,6 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +import java.util.function.Consumer;
 +import java.util.function.Function;
 +import java.util.function.Predicate;
-+import java.util.stream.Stream;
 +
 +public final class PaperTickList<T> extends TickListServer<T> { // extend to avoid breaking ABI
 +
@@ -268,7 +266,7 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +    }
 +
 +    private void prepare() {
-+        final long currentTick = this.world.getTime();
++        final long currentTick = this.nextTick;
 +
 +        final ChunkProviderServer chunkProvider = this.world.getChunkProvider();
 +
@@ -333,8 +331,18 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +        }
 +    }
 +
++    private boolean warnedAboutDesync;
++
 +    @Override
 +    public void tick() {
++        ++this.nextTick;
++        if (this.nextTick != this.world.getTime()) {
++            if (!this.warnedAboutDesync) {
++                this.warnedAboutDesync = true;
++                MinecraftServer.LOGGER.error("World tick desync detected! Expected " + this.nextTick + " ticks, but got " + this.world.getTime() + " ticks for world '" + this.world.getWorld().getName() + "'", new Throwable());
++                MinecraftServer.LOGGER.error("Preventing redstone from breaking by refusing to accept new tick time");
++            }
++        }
 +        final ChunkProviderServer chunkProvider = this.world.getChunkProvider();
 +
 +        this.world.getMethodProfiler().enter("cleaning");
@@ -345,7 +353,6 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +        // this must be done here in case something schedules in the tick code
 +        this.shortScheduled[this.shortScheduledIndex].clear();
 +        this.shortScheduledIndex = getNextIndex(this.shortScheduledIndex, SHORT_SCHEDULE_TICK_THRESHOLD);
-+        this.nextTick = this.world.getTime() + 1;
 +
 +        this.timingCleanup.stopTiming();
 +        this.world.getMethodProfiler().exitEnter("ticking");
@@ -472,7 +479,7 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +
 +    @Override
 +    public void schedule(BlockPosition blockPosition, T t, int i, TickListPriority tickListPriority) {
-+        this.schedule(blockPosition, t, i + this.world.getTime(), tickListPriority);
++        this.schedule(blockPosition, t, i + this.nextTick, tickListPriority);
 +    }
 +
 +    public void schedule(final NextTickListEntry<T> entry) {
@@ -644,7 +651,7 @@ index 0000000000000000000000000000000000000000..0692fe33bb7c4a7bb666920b10f5dd3a
 +        // start copy from TickListServer  // TODO check on update
 +        List<NextTickListEntry<T>> list = this.getEntriesInChunk(chunkcoordintpair, false, true);
 +
-+        return TickListServer.serialize(this.getMinecraftKeyFrom, list, this.world.getTime());
++        return TickListServer.serialize(this.getMinecraftKeyFrom, list, this.nextTick);
 +        // end copy from TickListServer
 +    }
 +
@@ -1032,6 +1039,35 @@ index 7873db26b336c97f909e5391e58ee53feaf59b9a..447eb2ba84789edf9bac2e2ffb2dec7c
      public boolean b(BaseBlockPosition baseblockposition) {
          return baseblockposition.getX() >= this.a && baseblockposition.getX() <= this.d && baseblockposition.getZ() >= this.c && baseblockposition.getZ() <= this.f && baseblockposition.getY() >= this.b && baseblockposition.getY() <= this.e;
      }
+diff --git a/src/main/java/net/minecraft/server/TickListChunk.java b/src/main/java/net/minecraft/server/TickListChunk.java
+index f94234b0a247e378ff9056d6c418464d619a356b..8af1229c3da63a838b0bec1cafde1e41cf5cf551 100644
+--- a/src/main/java/net/minecraft/server/TickListChunk.java
++++ b/src/main/java/net/minecraft/server/TickListChunk.java
+@@ -57,6 +57,8 @@ public class TickListChunk<T> implements TickList<T> {
+         return nbttaglist;
+     }
+ 
++    private static final int MAX_TICK_DELAY = Integer.getInteger("paper.ticklist-max-tick-delay", -1).intValue(); // Paper - clean up broken entries
++
+     public static <T> TickListChunk<T> a(NBTTagList nbttaglist, Function<T, MinecraftKey> function, Function<MinecraftKey, T> function1) {
+         List<TickListChunk.a<T>> list = Lists.newArrayList();
+ 
+@@ -67,7 +69,14 @@ public class TickListChunk<T> implements TickList<T> {
+             if (t0 != null) {
+                 BlockPosition blockposition = new BlockPosition(nbttagcompound.getInt("x"), nbttagcompound.getInt("y"), nbttagcompound.getInt("z"));
+ 
+-                list.add(new TickListChunk.a<>(t0, blockposition, nbttagcompound.getInt("t"), TickListPriority.a(nbttagcompound.getInt("p"))));
++                // Paper start - clean up broken entries
++                int delay = nbttagcompound.getInt("t");
++                if (MAX_TICK_DELAY > 0 && delay > MAX_TICK_DELAY) {
++                    MinecraftServer.LOGGER.warn("Dropping tick for pos " + blockposition + ", tick delay " + delay);
++                    continue;
++                }
++                list.add(new TickListChunk.a<>(t0, blockposition, delay, TickListPriority.a(nbttagcompound.getInt("p"))));
++                // Paper end - clean up broken entries
+             }
+         }
+ 
 diff --git a/src/main/java/net/minecraft/server/TickListServer.java b/src/main/java/net/minecraft/server/TickListServer.java
 index 3b8f56c0f0507ebdd9ac20be70688b4c0cfe4cf8..149d2b4f929c11b8baf17163bbd6ff8220a95e86 100644
 --- a/src/main/java/net/minecraft/server/TickListServer.java
diff --git a/Spigot-Server-Patches/0550-Fix-some-rails-connecting-improperly.patch b/Spigot-Server-Patches/0550-Fix-some-rails-connecting-improperly.patch
new file mode 100644
index 0000000000..0a3ad634bc
--- /dev/null
+++ b/Spigot-Server-Patches/0550-Fix-some-rails-connecting-improperly.patch
@@ -0,0 +1,95 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <[email protected]>
+Date: Fri, 24 Jul 2020 15:56:05 -0700
+Subject: [PATCH] Fix some rails connecting improperly
+
+
+diff --git a/src/main/java/net/minecraft/server/BlockMinecartDetector.java b/src/main/java/net/minecraft/server/BlockMinecartDetector.java
+index 06926c4ae1100c5848206b2c45d51e87f273416d..b8e91fca957c8a39c9fbf4f87c089c4ce710c8e0 100644
+--- a/src/main/java/net/minecraft/server/BlockMinecartDetector.java
++++ b/src/main/java/net/minecraft/server/BlockMinecartDetector.java
+@@ -50,6 +50,7 @@ public class BlockMinecartDetector extends BlockMinecartTrackAbstract {
+     }
+ 
+     private void a(World world, BlockPosition blockposition, IBlockData iblockdata) {
++        if (iblockdata.getBlock() != this) { return; } // Paper - not our block, don't do anything
+         boolean flag = (Boolean) iblockdata.get(BlockMinecartDetector.POWERED);
+         boolean flag1 = false;
+         List<EntityMinecartAbstract> list = this.a(world, blockposition, EntityMinecartAbstract.class, (Predicate) null);
+diff --git a/src/main/java/net/minecraft/server/BlockMinecartTrackAbstract.java b/src/main/java/net/minecraft/server/BlockMinecartTrackAbstract.java
+index d91b1b41aa2e3d3a12ebc52d19358032124135fb..a540b3e226b985f22daf1a69bf4e8cb578ab1476 100644
+--- a/src/main/java/net/minecraft/server/BlockMinecartTrackAbstract.java
++++ b/src/main/java/net/minecraft/server/BlockMinecartTrackAbstract.java
+@@ -46,6 +46,7 @@ public abstract class BlockMinecartTrackAbstract extends Block {
+         iblockdata = this.a(world, blockposition, iblockdata, true);
+         if (this.c) {
+             iblockdata.doPhysics(world, blockposition, this, blockposition, flag);
++            iblockdata = world.getType(blockposition); // Paper - don't desync, update again
+         }
+ 
+         return iblockdata;
+diff --git a/src/main/java/net/minecraft/server/MinecartTrackLogic.java b/src/main/java/net/minecraft/server/MinecartTrackLogic.java
+index 10bc2165159514d484e73a3acd08ca5929be72f2..e0be3a425aae51e1aced8eb6d8a5e84fc9315e3a 100644
+--- a/src/main/java/net/minecraft/server/MinecartTrackLogic.java
++++ b/src/main/java/net/minecraft/server/MinecartTrackLogic.java
+@@ -7,13 +7,19 @@ import javax.annotation.Nullable;
+ 
+ public class MinecartTrackLogic {
+ 
+-    private final World a;
+-    private final BlockPosition b;
++    private final World a; public final World getWorld() { return this.a; } // Paper - OBFHELPER
++    private final BlockPosition b; public final BlockPosition getPos() { return this.b; } // Paper - OBFHELPER
+     private final BlockMinecartTrackAbstract c;
+-    private IBlockData d;
++    private IBlockData d; public final IBlockData getRailState() { return this.d; } // Paper - OBFHELPER
+     private final boolean e;
+     private final List<BlockPosition> f = Lists.newArrayList();
+ 
++    // Paper start - prevent desync
++    public boolean isValid() {
++        return this.getWorld().getType(this.getPos()).getBlock() == this.getRailState().getBlock();
++    }
++    // Paper end - prevent desync
++
+     public MinecartTrackLogic(World world, BlockPosition blockposition, IBlockData iblockdata) {
+         this.a = world;
+         this.b = blockposition;
+@@ -148,6 +154,11 @@ public class MinecartTrackLogic {
+     }
+ 
+     private void c(MinecartTrackLogic minecarttracklogic) {
++        // Paper start - prevent desync
++        if (!this.isValid() || !minecarttracklogic.isValid()) {
++            return;
++        }
++        // Paper end - prevent desync
+         this.f.add(minecarttracklogic.b);
+         BlockPosition blockposition = this.b.north();
+         BlockPosition blockposition1 = this.b.south();
+@@ -342,11 +353,16 @@ public class MinecartTrackLogic {
+         this.d = (IBlockData) this.d.set(this.c.d(), blockpropertytrackposition1);
+         if (flag1 || this.a.getType(this.b) != this.d) {
+             this.a.setTypeAndData(this.b, this.d, 3);
++            // Paper start - prevent desync
++            if (!this.isValid()) {
++                return this;
++            }
++            // Paper end - prevent desync
+ 
+             for (int i = 0; i < this.f.size(); ++i) {
+                 MinecartTrackLogic minecarttracklogic = this.b((BlockPosition) this.f.get(i));
+ 
+-                if (minecarttracklogic != null) {
++                if (minecarttracklogic != null && minecarttracklogic.isValid()) { // Paper - prevent desync
+                     minecarttracklogic.d();
+                     if (minecarttracklogic.b(this)) {
+                         minecarttracklogic.c(this);
+@@ -359,6 +375,6 @@ public class MinecartTrackLogic {
+     }
+ 
+     public IBlockData c() {
+-        return this.d;
++        return this.getWorld().getType(this.getPos()); // Paper - prevent desync
+     }
+ }