Paper/patches/server/0723-Don-t-use-level-random-in-entity-constructors.patch
Bjarne Koll c5a10665b8
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.
2024-09-19 16:36:07 +02:00

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2.5 KiB
Diff

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Sun, 10 Jul 2022 14:13:22 -0700
Subject: [PATCH] Don't use level random in entity constructors
Paper makes the entity random thread-safe
and constructing an entity off the main thread
should be supported. Some entities (for whatever
reason) use the level's random in some places.
diff --git a/src/main/java/net/minecraft/world/entity/item/ItemEntity.java b/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
index df90d5b934f41f5d8c232e93830d6690b6ccf401..446c319524183d6a1b4d0e6f0613a8db690677da 100644
--- a/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
+++ b/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
@@ -72,7 +72,12 @@ public class ItemEntity extends Entity implements TraceableEntity {
}
public ItemEntity(Level world, double x, double y, double z, ItemStack stack) {
- this(world, x, y, z, stack, world.random.nextDouble() * 0.2D - 0.1D, 0.2D, world.random.nextDouble() * 0.2D - 0.1D);
+ // Paper start - Don't use level random in entity constructors (to make them thread-safe)
+ this(EntityType.ITEM, world);
+ this.setPos(x, y, z);
+ this.setDeltaMovement(this.random.nextDouble() * 0.2D - 0.1D, 0.2D, this.random.nextDouble() * 0.2D - 0.1D);
+ this.setItem(stack);
+ // Paper end - Don't use level random in entity constructors
}
public ItemEntity(Level world, double x, double y, double z, ItemStack stack, double velocityX, double velocityY, double velocityZ) {
diff --git a/src/main/java/net/minecraft/world/entity/item/PrimedTnt.java b/src/main/java/net/minecraft/world/entity/item/PrimedTnt.java
index 47f2a480f6a4b15e55cedbfa8a58459d33516a97..42bd2d9a1528b6210e4dfb56233062fd97c9743b 100644
--- a/src/main/java/net/minecraft/world/entity/item/PrimedTnt.java
+++ b/src/main/java/net/minecraft/world/entity/item/PrimedTnt.java
@@ -62,7 +62,7 @@ public class PrimedTnt extends Entity implements TraceableEntity {
public PrimedTnt(Level world, double x, double y, double z, @Nullable LivingEntity igniter) {
this(EntityType.TNT, world);
this.setPos(x, y, z);
- double d3 = world.random.nextDouble() * 6.2831854820251465D;
+ double d3 = this.random.nextDouble() * 6.2831854820251465D; // Paper - Don't use level random in entity constructors
this.setDeltaMovement(-Math.sin(d3) * 0.02D, 0.20000000298023224D, -Math.cos(d3) * 0.02D);
this.setFuse(80);