From 950a84c337f317388cf39a3820125e049c598b8d Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 18 Apr 2022 14:39:13 +0200
Subject: Optimize header cache some more by storing hash in key

---
 libbuild2/cc/module.hxx | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

(limited to 'libbuild2/cc/module.hxx')

diff --git a/libbuild2/cc/module.hxx b/libbuild2/cc/module.hxx
index ee9349a..2a8611b 100644
--- a/libbuild2/cc/module.hxx
+++ b/libbuild2/cc/module.hxx
@@ -86,8 +86,30 @@ namespace build2
       // sharing it for the entire weak amalgamation.
       //
     public:
+      // Keep the hash in the key. This way we can compute it outside of the
+      // lock.
+      //
+      struct header_key
+      {
+        path   file;
+        size_t hash;
+
+        friend bool
+        operator== (const header_key& x, const header_key& y)
+        {
+          return x.file == y.file; // Note: hash was already compared.
+        }
+      };
+
+      struct header_key_hasher
+      {
+        size_t operator() (const header_key& k) const {return k.hash;}
+      };
+
       mutable shared_mutex                          header_map_mutex;
-      mutable std::unordered_map<path, const file*> header_map;
+      mutable std::unordered_map<header_key,
+                                 const file*,
+                                 header_key_hasher> header_map;
 
     private:
       // Defined in gcc.cxx.
-- 
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