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, 18 insertions, 0 deletions

diff --git a/patches/server/0759-Ignore-impossible-spawn-tick.patch b/patches/server/0759-Ignore-impossible-spawn-tick.patch
new file mode 100644
index 0000000000..f046102ceb
--- /dev/null
+++ b/patches/server/0759-Ignore-impossible-spawn-tick.patch
@@ -0,0 +1,18 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: dannyball710 <[email protected]>
+Date: Sat, 12 Feb 2022 23:42:48 +0800
+Subject: [PATCH] Ignore impossible spawn tick
+
+
+diff --git a/src/main/java/net/minecraft/world/level/BaseSpawner.java b/src/main/java/net/minecraft/world/level/BaseSpawner.java
+index 8efc06d29c62fa2be8515ed3359d52a6d4b807d2..f57e1b78204dff661ad5d3ee93a88a00330af2dc 100644
+--- a/src/main/java/net/minecraft/world/level/BaseSpawner.java
++++ b/src/main/java/net/minecraft/world/level/BaseSpawner.java
+@@ -84,6 +84,7 @@ public abstract class BaseSpawner {
+     }
+ 
+     public void serverTick(ServerLevel world, BlockPos pos) {
++        if (spawnCount <= 0 || maxNearbyEntities <= 0) return; // Paper - Ignore impossible spawn tick
+         // Paper start - Configurable mob spawner tick rate
+         if (spawnDelay > 0 && --tickDelay > 0) return;
+         tickDelay = world.paperConfig().tickRates.mobSpawner;