From 7f9b5226af81607fac499807140632b4a59e598e Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Sun, 7 Sep 2025 16:54:39 +0200
Subject: [PATCH] Add getConcurrent helper function

---
 src/libutil/include/nix/util/util.hh | 11 +++++++++++
 src/libutil/posix-source-accessor.cc |  4 +---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/libutil/include/nix/util/util.hh b/src/libutil/include/nix/util/util.hh
index 561550c41..a20305a6f 100644
--- a/src/libutil/include/nix/util/util.hh
+++ b/src/libutil/include/nix/util/util.hh
@@ -218,6 +218,17 @@ typename T::mapped_type * get(T & map, K & key)
 template<class T>
 typename T::mapped_type * get(T && map, const typename T::key_type & key) = delete;
 
+/**
+ * Look up a value in a `boost::concurrent_flat_map`.
+ */
+template<class T>
+std::optional<typename T::mapped_type> getConcurrent(const T & map, const typename T::key_type & key)
+{
+    std::optional<typename T::mapped_type> res;
+    map.cvisit(key, [&](auto & x) { res = x.second; });
+    return res;
+}
+
 /**
  * Get a value for the specified key from an associate container, or a default value if the key isn't present.
  */
diff --git a/src/libutil/posix-source-accessor.cc b/src/libutil/posix-source-accessor.cc
index 877c63331..c524f3e4f 100644
--- a/src/libutil/posix-source-accessor.cc
+++ b/src/libutil/posix-source-accessor.cc
@@ -95,9 +95,7 @@ std::optional<struct stat> PosixSourceAccessor::cachedLstat(const CanonPath & pa
     // former is not hashable on libc++.
     Path absPath = makeAbsPath(path).string();
 
-    std::optional<Cache::mapped_type> res;
-    cache.cvisit(absPath, [&](auto & x) { res.emplace(x.second); });
-    if (res)
+    if (auto res = getConcurrent(cache, absPath))
         return *res;
 
     auto st = nix::maybeLstat(absPath.c_str());