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, 26 insertions, 0 deletions

diff --git a/patches/server/0485-added-option-to-disable-pathfinding-updates-on-block.patch b/patches/server/0485-added-option-to-disable-pathfinding-updates-on-block.patch
new file mode 100644
index 0000000000..e40ef31e16
--- /dev/null
+++ b/patches/server/0485-added-option-to-disable-pathfinding-updates-on-block.patch
@@ -0,0 +1,26 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: lukas81298 <[email protected]>
+Date: Mon, 25 Jan 2021 14:37:57 +0100
+Subject: [PATCH] added option to disable pathfinding updates on block changes
+
+
+diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
+index 644341b8bc3079c6f092226acd11667f64bd55a1..1fe013b94cf1b5332f1e4645dd35df01e11fe0d9 100644
+--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
++++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
+@@ -1374,6 +1374,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
+ 
+         this.getChunkSource().blockChanged(pos);
+         this.pathTypesByPosCache.invalidate(pos);
++        if (this.paperConfig().misc.updatePathfindingOnBlockUpdate) { // Paper - option to disable pathfinding updates
+         VoxelShape voxelshape = oldState.getCollisionShape(this, pos);
+         VoxelShape voxelshape1 = newState.getCollisionShape(this, pos);
+ 
+@@ -1415,6 +1416,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
+             }
+ 
+         }
++        } // Paper - option to disable pathfinding updates
+     }
+ 
+     @Override