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, 41 insertions, 0 deletions

diff --git a/patches/server/0627-Prevent-excessive-velocity-through-repeated-crits.patch b/patches/server/0627-Prevent-excessive-velocity-through-repeated-crits.patch
new file mode 100644
index 0000000000..10ce91923a
--- /dev/null
+++ b/patches/server/0627-Prevent-excessive-velocity-through-repeated-crits.patch
@@ -0,0 +1,41 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Nassim Jahnke <[email protected]>
+Date: Thu, 25 Nov 2021 10:25:09 +0100
+Subject: [PATCH] Prevent excessive velocity through repeated crits
+
+
+diff --git a/src/main/java/net/minecraft/world/entity/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+index 4132b5dfbc6a7693f0bb923a8b14ded571560030..ee7bb1a01bf027eb7b28e3795950a17e5f686815 100644
+--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
++++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
+@@ -2773,17 +2773,29 @@ public abstract class LivingEntity extends Entity implements Attackable {
+         return this.hasEffect(MobEffects.JUMP) ? 0.1F * ((float) this.getEffect(MobEffects.JUMP).getAmplifier() + 1.0F) : 0.0F;
+     }
+ 
++    protected long lastJumpTime = 0L; // Paper - Prevent excessive velocity through repeated crits
+     @VisibleForTesting
+     public void jumpFromGround() {
+         float f = this.getJumpPower();
+ 
+         if (f > 1.0E-5F) {
+             Vec3 vec3d = this.getDeltaMovement();
++            // Paper start - Prevent excessive velocity through repeated crits
++            long time = System.nanoTime();
++            boolean canCrit = true;
++            if (this instanceof net.minecraft.world.entity.player.Player) {
++                canCrit = false;
++                if (time - this.lastJumpTime > (long)(0.250e9)) {
++                    this.lastJumpTime = time;
++                    canCrit = true;
++                }
++            }
++            // Paper end - Prevent excessive velocity through repeated crits
+ 
+             this.setDeltaMovement(vec3d.x, (double) f, vec3d.z);
+             if (this.isSprinting()) {
+                 float f1 = this.getYRot() * 0.017453292F;
+-
++                if (canCrit) // Paper - Prevent excessive velocity through repeated crits
+                 this.addDeltaMovement(new Vec3((double) (-Mth.sin(f1)) * 0.2D, 0.0D, (double) Mth.cos(f1) * 0.2D));
+             }
+