From 1179c8ee7c55d4831a0607401376b0d5de7262c1 Mon Sep 17 00:00:00 2001
From: d-netto <diogonetto.dcn@gmail.com>
Date: Thu, 16 Nov 2023 13:51:53 -0300
Subject: [PATCH] cap the number of GC threads to number of cpu cores

---
 src/threading.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/threading.c b/src/threading.c
index 18c502cf94387..962274401d57b 100644
--- a/src/threading.c
+++ b/src/threading.c
@@ -709,6 +709,13 @@ void jl_init_threading(void)
             else {
                 jl_n_markthreads = (nthreads / 2) - 1;
             }
+            // if `--gcthreads` or ENV[NUM_GCTHREADS_NAME] was not specified,
+            // cap the number of threads that may run the mark phase to
+            // the number of CPU cores
+            int cpu = jl_cpu_threads();
+            if (jl_n_markthreads + 1 >= cpu) {
+                jl_n_markthreads = cpu - 1;
+            }
         }
     }
     int16_t ngcthreads = jl_n_markthreads + jl_n_sweepthreads;