From fbbca59453fcbc91ff63256b617523b5962b28f8 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Fri, 31 May 2024 19:18:38 +0200
Subject: [PATCH] Make RegexCache thread-safe

---
 src/libexpr/primops.cc | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 22d7f188f..9177b0a2f 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -4062,17 +4062,23 @@ static RegisterPrimOp primop_convertHash({
 
 struct RegexCache
 {
-    // TODO use C++20 transparent comparison when available
-    std::unordered_map<std::string_view, std::regex> cache;
-    std::list<std::string> keys;
+    struct State
+    {
+        // TODO use C++20 transparent comparison when available
+        std::unordered_map<std::string_view, std::regex> cache;
+        std::list<std::string> keys;
+    };
+
+    Sync<State> state_;
 
     std::regex get(std::string_view re)
     {
-        auto it = cache.find(re);
-        if (it != cache.end())
+        auto state(state_.lock());
+        auto it = state->cache.find(re);
+        if (it != state->cache.end())
             return it->second;
-        keys.emplace_back(re);
-        return cache.emplace(keys.back(), std::regex(keys.back(), std::regex::extended)).first->second;
+        state->keys.emplace_back(re);
+        return state->cache.emplace(state->keys.back(), std::regex(state->keys.back(), std::regex::extended)).first->second;
     }
 };