From 0b4cb29386d34195d3030ce2cfb423866f39a775 Mon Sep 17 00:00:00 2001
From: Aaron O'Mullan <aaron.omullan@gmail.com>
Date: Fri, 9 Apr 2021 19:49:11 +0200
Subject: [PATCH] perf(core): use BTreeMap for GothamState (#10073)

This commit replaces GothamState's internal HashMap
with a BTreeMap to improve performance.

OpState/GothamState keys by TypeId which is essentially
an opaque u64. For small sets of integer keys BTreeMap
outperforms HashMap mainly since it removes the hashing
overhead and Eq/Comp on integer-like types is very cheap,
it should also have a smaller memory footprint.

We only use ~30 unique types and thus ~30 unique keys to
access OpState, so the keyset is small and immutable
throughout the life of a JsRuntime, there's no meaningful
churn in keys added/removed.
---
 core/gotham_state.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/gotham_state.rs b/core/gotham_state.rs
index fa22878bba..b8f42137f5 100644
--- a/core/gotham_state.rs
+++ b/core/gotham_state.rs
@@ -6,11 +6,11 @@
 use log::trace;
 use std::any::Any;
 use std::any::TypeId;
-use std::collections::HashMap;
+use std::collections::BTreeMap;
 
 #[derive(Default)]
 pub struct GothamState {
-  data: HashMap<TypeId, Box<dyn Any>>,
+  data: BTreeMap<TypeId, Box<dyn Any>>,
 }
 
 impl GothamState {