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, 27 insertions, 0 deletions

diff --git a/patches/server/0502-Drop-carried-item-when-player-has-disconnected.patch b/patches/server/0502-Drop-carried-item-when-player-has-disconnected.patch
new file mode 100644
index 0000000000..ababb3984c
--- /dev/null
+++ b/patches/server/0502-Drop-carried-item-when-player-has-disconnected.patch
@@ -0,0 +1,27 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Dmitry Sidorov <[email protected]>
+Date: Thu, 4 Feb 2021 20:32:01 +0300
+Subject: [PATCH] Drop carried item when player has disconnected
+
+Fixes disappearance of held items, when a player gets disconnected and PlayerDropItemEvent is cancelled.
+Closes #5036
+
+diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
+index 123fe4f5b98a7483af86695ec82987abd45eafb2..bbc6f64a3b2c0702a0a752acd48145cdcafd742e 100644
+--- a/src/main/java/net/minecraft/server/players/PlayerList.java
++++ b/src/main/java/net/minecraft/server/players/PlayerList.java
+@@ -588,6 +588,14 @@ public abstract class PlayerList {
+         }
+         // Paper end - Configurable player collision
+ 
++        // Paper - Drop carried item when player has disconnected
++        if (!entityplayer.containerMenu.getCarried().isEmpty()) {
++            net.minecraft.world.item.ItemStack carried = entityplayer.containerMenu.getCarried();
++            entityplayer.containerMenu.setCarried(net.minecraft.world.item.ItemStack.EMPTY);
++            entityplayer.drop(carried, false);
++        }
++        // Paper end - Drop carried item when player has disconnected
++
+         this.save(entityplayer);
+         if (entityplayer.isPassenger()) {
+             Entity entity = entityplayer.getRootVehicle();