From d8dbc2dcba43ff36221f6549205d2d4cf64b760c Mon Sep 17 00:00:00 2001
From: Matt Valentine-House <matt@eightbitraptor.com>
Date: Thu, 5 Dec 2024 14:41:05 +0000
Subject: [ruby/mmtk] Support setting the mmtk thread count with MMTK_THREADS

https://github.com/ruby/mmtk/commit/e4d6b56824
---
 gc/mmtk/src/api.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gc/mmtk/src/api.rs b/gc/mmtk/src/api.rs
index b3d4c90f87..ae626a4a0f 100644
--- a/gc/mmtk/src/api.rs
+++ b/gc/mmtk/src/api.rs
@@ -44,6 +44,11 @@ pub extern "C" fn mmtk_builder_default() -> *mut MMTKBuilder {
 
     const DEFAULT_HEAP_MIN: usize = 1 << 20;
 
+    let mmtk_threads: usize = std::env::var("MMTK_THREADS")
+        .unwrap_or("0".to_string())
+        .parse::<usize>()
+        .unwrap_or(0);
+
     let mut mmtk_heap_min = match std::env::var("MMTK_HEAP_MIN") {
         Ok(min) => {
             let capa = parse_capacity(&min, DEFAULT_HEAP_MIN);
@@ -90,6 +95,10 @@ pub extern "C" fn mmtk_builder_default() -> *mut MMTKBuilder {
     // Between 1MiB and 500MiB
     builder.options.gc_trigger.set(mmtk_mode);
 
+    if mmtk_threads > 0 {
+        builder.options.threads.set(mmtk_threads);
+    }
+
     Box::into_raw(Box::new(builder))
 }
 
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