Remove wall-time / unused skip tick protection (#11412)

Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.

To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.

These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.

Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.

1 files changed, 90 insertions, 0 deletions

diff --git a/patches/server/0593-Add-Raw-Byte-Entity-Serialization.patch b/patches/server/0593-Add-Raw-Byte-Entity-Serialization.patch
new file mode 100644
index 0000000000..3ad09b5cc5
--- /dev/null
+++ b/patches/server/0593-Add-Raw-Byte-Entity-Serialization.patch
@@ -0,0 +1,90 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Mariell Hoversholm <[email protected]>
+Date: Sun, 24 Oct 2021 16:20:31 -0400
+Subject: [PATCH] Add Raw Byte Entity Serialization
+
+== AT ==
+public net.minecraft.world.entity.Entity setLevel(Lnet/minecraft/world/level/Level;)V
+
+diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
+index 836356ecb3c91fd7886ac9ae83f1cc835469e198..f21bf6c8bbf30c59f1588c2105dbd7f80c07a0f1 100644
+--- a/src/main/java/net/minecraft/world/entity/Entity.java
++++ b/src/main/java/net/minecraft/world/entity/Entity.java
+@@ -2144,6 +2144,15 @@ public abstract class Entity implements SyncedDataHolder, Nameable, EntityAccess
+         }
+     }
+ 
++    // Paper start - Entity serialization api
++    public boolean serializeEntity(CompoundTag compound) {
++        List<Entity> pass = new java.util.ArrayList<>(this.getPassengers());
++        this.passengers = ImmutableList.of();
++        boolean result = save(compound);
++        this.passengers = ImmutableList.copyOf(pass);
++        return result;
++    }
++    // Paper end - Entity serialization api
+     public boolean save(CompoundTag nbt) {
+         return this.isPassenger() ? false : this.saveAsPassenger(nbt);
+     }
+diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+index 7c04eb9e7eb5ff728465b46e3739eb2598ef1204..6fab713531665298d3b03e7960a17ecb1471a6d7 100644
+--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
++++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+@@ -1087,6 +1087,18 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
+     }
+     // Paper end - tracked players API
+ 
++    // Paper start - raw entity serialization API
++    @Override
++    public boolean spawnAt(Location location, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason reason) {
++        Preconditions.checkNotNull(location, "location cannot be null");
++        Preconditions.checkNotNull(reason, "reason cannot be null");
++        this.entity.setLevel(((CraftWorld) location.getWorld()).getHandle());
++        this.entity.setPos(location.getX(), location.getY(), location.getZ());
++        this.entity.setRot(location.getYaw(), location.getPitch());
++        return !this.entity.valid && this.entity.level().addFreshEntity(this.entity, reason);
++    }
++    // Paper end - raw entity serialization API
++
+     // Paper start - missing entity api
+     @Override
+     public boolean isInvisible() {  // Paper - moved up from LivingEntity
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+index 95a6f26f75efda7db41db9091107502e8d4e0453..0e849b49329054005c20a5773de2ff15bf3f6e5d 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+@@ -488,7 +488,33 @@ public final class CraftMagicNumbers implements UnsafeValues {
+         return CraftItemStack.asCraftMirror(net.minecraft.world.item.ItemStack.parse(MinecraftServer.getServer().registryAccess(), compound).orElseThrow());
+     }
+ 
+-    private byte[] serializeNbtToBytes(CompoundTag compound) {
++    @Override
++    public byte[] serializeEntity(org.bukkit.entity.Entity entity) {
++        Preconditions.checkNotNull(entity, "null cannot be serialized");
++        Preconditions.checkArgument(entity instanceof org.bukkit.craftbukkit.entity.CraftEntity, "only CraftEntities can be serialized");
++
++        net.minecraft.nbt.CompoundTag compound = new net.minecraft.nbt.CompoundTag();
++        ((org.bukkit.craftbukkit.entity.CraftEntity) entity).getHandle().serializeEntity(compound);
++        return serializeNbtToBytes(compound);
++    }
++
++    @Override
++    public org.bukkit.entity.Entity deserializeEntity(byte[] data, org.bukkit.World world, boolean preserveUUID) {
++        Preconditions.checkNotNull(data, "null cannot be deserialized");
++        Preconditions.checkArgument(data.length > 0, "cannot deserialize nothing");
++
++        net.minecraft.nbt.CompoundTag compound = deserializeNbtFromBytes(data);
++        int dataVersion = compound.getInt("DataVersion");
++        compound = (net.minecraft.nbt.CompoundTag) MinecraftServer.getServer().fixerUpper.update(References.ENTITY, new Dynamic<>(NbtOps.INSTANCE, compound), dataVersion, this.getDataVersion()).getValue();
++        if (!preserveUUID) {
++            // Generate a new UUID so we don't have to worry about deserializing the same entity twice
++            compound.remove("UUID");
++        }
++        return net.minecraft.world.entity.EntityType.create(compound, ((org.bukkit.craftbukkit.CraftWorld) world).getHandle())
++            .orElseThrow(() -> new IllegalArgumentException("An ID was not found for the data. Did you downgrade?")).getBukkitEntity();
++    }
++
++    private byte[] serializeNbtToBytes(net.minecraft.nbt.CompoundTag compound) {
+         compound.putInt("DataVersion", getDataVersion());
+         java.io.ByteArrayOutputStream outputStream = new java.io.ByteArrayOutputStream();
+         try {