From 97994c77fb5b82ca959e1188ecaee7d633d60a8e Mon Sep 17 00:00:00 2001
From: Luke Gruber <luke.gruber@shopify.com>
Date: Thu, 12 Jun 2025 11:10:29 -0400
Subject: [PATCH] Only use regex internal reg_cache when in main ractor

Using this `reg_cache` is racy across ractors, so don't use it when in a
ractor. Also, its use across ractors can cause a regular expression created
in 1 ractor to be used in another ractor (an isolation bug).
---
 common.mk |  3 +++
 re.c      | 15 ++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/common.mk b/common.mk
index 98f4baf938..f94ad33d88 100644
--- a/common.mk
+++ b/common.mk
@@ -15119,6 +15119,8 @@ re.$(OBJEXT): {$(VPATH)}missing.h
 re.$(OBJEXT): {$(VPATH)}node.h
 re.$(OBJEXT): {$(VPATH)}onigmo.h
 re.$(OBJEXT): {$(VPATH)}oniguruma.h
+re.$(OBJEXT): {$(VPATH)}ractor.h
+re.$(OBJEXT): {$(VPATH)}ractor_core.h
 re.$(OBJEXT): {$(VPATH)}re.c
 re.$(OBJEXT): {$(VPATH)}re.h
 re.$(OBJEXT): {$(VPATH)}regenc.h
@@ -15134,6 +15136,7 @@ re.$(OBJEXT): {$(VPATH)}thread_$(THREAD_MODEL).h
 re.$(OBJEXT): {$(VPATH)}thread_native.h
 re.$(OBJEXT): {$(VPATH)}util.h
 re.$(OBJEXT): {$(VPATH)}vm_core.h
+re.$(OBJEXT): {$(VPATH)}vm_debug.h
 re.$(OBJEXT): {$(VPATH)}vm_opts.h
 regcomp.$(OBJEXT): $(hdrdir)/ruby.h
 regcomp.$(OBJEXT): $(hdrdir)/ruby/ruby.h
diff --git a/re.c b/re.c
index 3cf99c1210..e666a7c3d4 100644
--- a/re.c
+++ b/re.c
@@ -28,6 +28,7 @@
 #include "ruby/encoding.h"
 #include "ruby/re.h"
 #include "ruby/util.h"
+#include "ractor_core.h"
 
 VALUE rb_eRegexpError, rb_eRegexpTimeoutError;
 
@@ -3499,12 +3500,16 @@ static VALUE reg_cache;
 VALUE
 rb_reg_regcomp(VALUE str)
 {
-    if (reg_cache && RREGEXP_SRC_LEN(reg_cache) == RSTRING_LEN(str)
-        && ENCODING_GET(reg_cache) == ENCODING_GET(str)
-        && memcmp(RREGEXP_SRC_PTR(reg_cache), RSTRING_PTR(str), RSTRING_LEN(str)) == 0)
-        return reg_cache;
+    if (rb_ractor_main_p()) {
+        if (reg_cache && RREGEXP_SRC_LEN(reg_cache) == RSTRING_LEN(str)
+            && ENCODING_GET(reg_cache) == ENCODING_GET(str)
+            && memcmp(RREGEXP_SRC_PTR(reg_cache), RSTRING_PTR(str), RSTRING_LEN(str)) == 0)
+            return reg_cache;
 
-    return reg_cache = rb_reg_new_str(str, 0);
+        return reg_cache = rb_reg_new_str(str, 0);
+    } else {
+        return rb_reg_new_str(str, 0);
+    }
 }
 
 static st_index_t reg_hash(VALUE re);