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, 47 insertions, 0 deletions

diff --git a/patches/server/0335-Optimize-Pathfinding.patch b/patches/server/0335-Optimize-Pathfinding.patch
new file mode 100644
index 0000000000..281988ce37
--- /dev/null
+++ b/patches/server/0335-Optimize-Pathfinding.patch
@@ -0,0 +1,47 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <[email protected]>
+Date: Thu, 3 Mar 2016 02:02:07 -0600
+Subject: [PATCH] Optimize Pathfinding
+
+Prevents pathfinding from spamming failures for things such as
+arrow attacks.
+
+diff --git a/src/main/java/net/minecraft/world/entity/ai/navigation/PathNavigation.java b/src/main/java/net/minecraft/world/entity/ai/navigation/PathNavigation.java
+index 188904c9f0f81db1d63eec953d6746f2dc23dc81..2e9991e6b3c05584002744a2ee2579b1dba218b2 100644
+--- a/src/main/java/net/minecraft/world/entity/ai/navigation/PathNavigation.java
++++ b/src/main/java/net/minecraft/world/entity/ai/navigation/PathNavigation.java
+@@ -192,13 +192,33 @@ public abstract class PathNavigation {
+         return this.moveTo(this.createPath(x, y, z, 1), speed);
+     }
+ 
++    // Paper start - Perf: Optimise pathfinding
++    private int lastFailure = 0;
++    private int pathfindFailures = 0;
++    // Paper end - Perf: Optimise pathfinding
++
+     public boolean moveTo(double x, double y, double z, int distance, double speed) {
+         return this.moveTo(this.createPath(x, y, z, distance), speed);
+     }
+ 
+     public boolean moveTo(Entity entity, double speed) {
++        // Paper start - Perf: Optimise pathfinding
++        if (this.pathfindFailures > 10 && this.path == null && net.minecraft.server.MinecraftServer.currentTick < this.lastFailure + 40) {
++            return false;
++        }
++        // Paper end - Perf: Optimise pathfinding
+         Path path = this.createPath(entity, 1);
+-        return path != null && this.moveTo(path, speed);
++        // Paper start - Perf: Optimise pathfinding
++        if (path != null && this.moveTo(path, speed)) {
++            this.lastFailure = 0;
++            this.pathfindFailures = 0;
++            return true;
++        } else {
++            this.pathfindFailures++;
++            this.lastFailure = net.minecraft.server.MinecraftServer.currentTick;
++            return false;
++        }
++        // Paper end - Perf: Optimise pathfinding
+     }
+ 
+     public boolean moveTo(@Nullable Path path, double speed) {