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, 81 insertions, 0 deletions

diff --git a/patches/server/1001-Entity-load-save-limit-per-chunk.patch b/patches/server/1001-Entity-load-save-limit-per-chunk.patch
new file mode 100644
index 0000000000..9a5959e34f
--- /dev/null
+++ b/patches/server/1001-Entity-load-save-limit-per-chunk.patch
@@ -0,0 +1,81 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jason Penilla <[email protected]>
+Date: Wed, 18 Nov 2020 20:52:25 -0800
+Subject: [PATCH] Entity load/save limit per chunk
+
+Adds a config option to limit the number of entities saved and loaded
+to a chunk. The default values of -1 disable the limit. Although
+defaults are only included for certain entites, this allows setting
+limits for any entity type.
+
+diff --git a/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/ChunkEntitySlices.java b/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/ChunkEntitySlices.java
+index 997b05167c19472acb98edac32d4548cc65efa8e..5c7f2471a0b15ac2e714527296ad2aa7291999eb 100644
+--- a/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/ChunkEntitySlices.java
++++ b/src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/level/entity/ChunkEntitySlices.java
+@@ -100,7 +100,18 @@ public final class ChunkEntitySlices {
+         }
+ 
+         final ListTag entitiesTag = new ListTag();
++        final java.util.Map<net.minecraft.world.entity.EntityType<?>, Integer> savedEntityCounts = new java.util.HashMap<>(); // Paper - Entity load/save limit per chunk
+         for (final Entity entity : entities) {
++            // Paper start - Entity load/save limit per chunk
++            final EntityType<?> entityType = entity.getType();
++            final int saveLimit = world.paperConfig().chunks.entityPerChunkSaveLimit.getOrDefault(entityType, -1);
++            if (saveLimit > -1) {
++                if (savedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
++                    continue;
++                }
++                savedEntityCounts.merge(entityType, 1, Integer::sum);
++            }
++            // Paper end - Entity load/save limit per chunk
+             CompoundTag compoundTag = new CompoundTag();
+             if (entity.save(compoundTag)) {
+                 entitiesTag.add(compoundTag);
+diff --git a/src/main/java/net/minecraft/world/entity/EntityType.java b/src/main/java/net/minecraft/world/entity/EntityType.java
+index 842b0cec0397d7ae5166617627340ffac0e35db1..cb61462d4691a055a4b25f7b953609d8a154fdfe 100644
+--- a/src/main/java/net/minecraft/world/entity/EntityType.java
++++ b/src/main/java/net/minecraft/world/entity/EntityType.java
+@@ -649,9 +649,20 @@ public class EntityType<T extends Entity> implements FeatureElement, EntityTypeT
+         final Spliterator<? extends Tag> spliterator = entityNbtList.spliterator();
+ 
+         return StreamSupport.stream(new Spliterator<Entity>() {
++            final java.util.Map<EntityType<?>, Integer> loadedEntityCounts = new java.util.HashMap<>(); // Paper - Entity load/save limit per chunk
+             public boolean tryAdvance(Consumer<? super Entity> consumer) {
+                 return spliterator.tryAdvance((nbtbase) -> {
+                     EntityType.loadEntityRecursive((CompoundTag) nbtbase, world, (entity) -> {
++                        // Paper start - Entity load/save limit per chunk
++                        final EntityType<?> entityType = entity.getType();
++                        final int saveLimit = world.paperConfig().chunks.entityPerChunkSaveLimit.getOrDefault(entityType, -1);
++                        if (saveLimit > -1) {
++                            if (this.loadedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
++                                return null;
++                            }
++                            this.loadedEntityCounts.merge(entityType, 1, Integer::sum);
++                        }
++                        // Paper end - Entity load/save limit per chunk
+                         consumer.accept(entity);
+                         return entity;
+                     });
+diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/EntityStorage.java b/src/main/java/net/minecraft/world/level/chunk/storage/EntityStorage.java
+index 503ac0374e0c9f9993ad37bb8bd8cf1570d3615a..d4a505ef4af9ded02aeb1a817bcbe5b1a912a5b3 100644
+--- a/src/main/java/net/minecraft/world/level/chunk/storage/EntityStorage.java
++++ b/src/main/java/net/minecraft/world/level/chunk/storage/EntityStorage.java
+@@ -92,7 +92,18 @@ public class EntityStorage implements EntityPersistentStorage<Entity> {
+             }
+         } else {
+             ListTag listTag = new ListTag();
++            final java.util.Map<net.minecraft.world.entity.EntityType<?>, Integer> savedEntityCounts = new java.util.HashMap<>(); // Paper - Entity load/save limit per chunk
+             dataList.getEntities().forEach(entity -> {
++                // Paper start - Entity load/save limit per chunk
++                final EntityType<?> entityType = entity.getType();
++                final int saveLimit = this.level.paperConfig().chunks.entityPerChunkSaveLimit.getOrDefault(entityType, -1);
++                if (saveLimit > -1) {
++                    if (savedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
++                        return;
++                    }
++                    savedEntityCounts.merge(entityType, 1, Integer::sum);
++                }
++                // Paper end - Entity load/save limit per chunk
+                 CompoundTag compoundTagx = new CompoundTag();
+                 if (entity.save(compoundTagx)) {
+                     listTag.add(compoundTagx);