From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: stonar96 Date: Sun, 17 Jan 2021 01:11:36 +0100 Subject: [PATCH] Optimize HashMapPalette HashMapPalette uses an instance of CrudeIncrementalIntIdentityHashBiMap internally. A Palette has a preset maximum size = 1 << bits. CrudeIncrementalIntIdentityHashBiMap has an initial size but is automatically resized. The CrudeIncrementalIntIdentityHashBiMap is created with the maximum size in the constructor of HashMapPalette, with the aim that it doesn't need to be resized anymore. However, there are two things that I think Mojang hasn't considered here: 1) The CrudeIncrementalIntIdentityHashBiMap is resized, when its initial size is reached and not the next time, when a further object is added. 2) HashMapPalette adds objects (unnecessarily) before checking if the initial size of CrudeIncrementalIntIdentityHashBiMap is reached. This means to actually avoid resize operations in CrudeIncrementalIntIdentityHashBiMap, one has to add 2 to the initial size or add 1 and check the size before adding objects. This commit implements the second approach. Note that this isn't only an optimization but also makes async reads of Palettes fail-safe. An async read while the CrudeIncrementalIntIdentityHashBiMap is resized is fatal and can even lead to corrupted data. This is also something that Anti-Xray is currently relying on. diff --git a/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java b/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java index 26e093243c70313b777483d9555fb1557443c9b8..7b7b614e5c3a30be89eeea2d25112fc9bcb3052c 100644 --- a/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java +++ b/src/main/java/net/minecraft/world/level/chunk/HashMapPalette.java @@ -20,7 +20,7 @@ public class HashMapPalette implements Palette { } public HashMapPalette(IdMap idList, int indexBits, PaletteResize listener) { - this(idList, indexBits, listener, CrudeIncrementalIntIdentityHashBiMap.create(1 << indexBits)); + this(idList, indexBits, listener, CrudeIncrementalIntIdentityHashBiMap.create((1 << indexBits) + 1)); // Paper - Avoid unnecessary resize operation in CrudeIncrementalIntIdentityHashBiMap } private HashMapPalette(IdMap idList, int indexBits, PaletteResize listener, CrudeIncrementalIntIdentityHashBiMap map) { @@ -38,10 +38,16 @@ public class HashMapPalette implements Palette { public int idFor(T object) { int i = this.values.getId(object); if (i == -1) { - i = this.values.add(object); - if (i >= 1 << this.bits) { + // Paper start - Avoid unnecessary resize operation in CrudeIncrementalIntIdentityHashBiMap and optimize + // We use size() instead of the result from add(K) + // This avoids adding another object unnecessarily + // Without this change, + 2 would be required in the constructor + if (this.values.size() >= 1 << this.bits) { i = this.resizeHandler.onResize(this.bits + 1, object); + } else { + i = this.values.add(object); } + // Paper end } return i;