From a3ff648f90c31cba2cc9e63fa93d61a310d33d95 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 4 Aug 2025 19:01:33 +0200
Subject: [PATCH] Call GC_allow_register_threads() to enable parallel marking
 in Boehm GC

---
 src/libexpr/eval-gc.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/libexpr/eval-gc.cc b/src/libexpr/eval-gc.cc
index 5a4ecf035..ce2bcae8a 100644
--- a/src/libexpr/eval-gc.cc
+++ b/src/libexpr/eval-gc.cc
@@ -53,6 +53,9 @@ static inline void initGCReal()
 
     GC_INIT();
 
+    /* Enable parallel marking. */
+    GC_allow_register_threads();
+
     /* Register valid displacements in case we are using alignment niches
        for storing the type information. This way tagged pointers are considered
        to be valid, even when they are not aligned. */