From a2511e3dc88a35f940c24b119800d2f9222edead Mon Sep 17 00:00:00 2001
From: Charles Oliver Nutter <headius@headius.com>
Date: Wed, 6 Nov 2024 18:06:15 -0600
Subject: [PATCH] Set group only if we don't do add logic

Setting the new group before the add logic causes breaks the
removal from the thread's old group. Instead, only directly set
the thread's group if we won't run the add logic.
---
 core/src/main/java/org/jruby/RubyThreadGroup.java | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/core/src/main/java/org/jruby/RubyThreadGroup.java b/core/src/main/java/org/jruby/RubyThreadGroup.java
index 652c4939b83..9518e013d41 100644
--- a/core/src/main/java/org/jruby/RubyThreadGroup.java
+++ b/core/src/main/java/org/jruby/RubyThreadGroup.java
@@ -95,12 +95,11 @@ public IRubyObject add(ThreadContext context, IRubyObject rubyThread, Block bloc
             }
         }
 
-        // always set group when added explicitly
-        thread.setThreadGroup(this);
-
         // we only add live threads
         if (thread.alive_p(context).isTrue()) {
             addDirectly(thread);
+        } else {
+            thread.setThreadGroup(this);
         }
         
         return this;