From 2d663b502da16d6dc480bff7f58297d176d04246 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Sat, 6 Aug 2011 19:45:43 +0000
Subject: =?UTF-8?q?*=20Cache=20the=20result=20of=20file=20evaluation=20(i.?=
 =?UTF-8?q?e,=20memoize=20evalFile()).=20=20This=20=20=20prevents=20files?=
 =?UTF-8?q?=20from=20being=20evaluated=20and=20stored=20as=20values=20mult?=
 =?UTF-8?q?iple=20=20=20times.=20=20For=20instance,=20evaluation=20of=20th?=
 =?UTF-8?q?e=20=E2=80=98system=E2=80=99=20attribute=20in=20NixOS=20=20=20c?=
 =?UTF-8?q?auses=20=E2=80=98nixpkgs/pkgs/lib/lists.nix=E2=80=99=20to=20be?=
 =?UTF-8?q?=20evaluated=202019=20times.?=
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  Caching gives a modest speedup and a decent memory footprint
  reduction (e.g., from 1.44s to 1.28s, and from 81 MiB to 59 MiB with
  GC_INITIAL_HEAP_SIZE=100000 on my system).
---
 src/libexpr/eval.hh | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'src/libexpr/eval.hh')

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 413234f2b..694d4407b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -211,8 +211,17 @@ private:
 
     bool allowUnsafeEquality;
 
+    /* A cache from path names to parse trees. */
     std::map<Path, Expr *> parseTrees;
 
+    /* A cache from path names to values. */
+#if HAVE_BOEHMGC
+    typedef std::map<Path, Value, std::less<Path>, gc_allocator<std::pair<const Path, Value> > > FileEvalCache;
+#else
+    typedef std::map<Path, Value> FileEvalCache;
+#endif
+    FileEvalCache fileEvalCache;
+
     typedef list<std::pair<string, Path> > SearchPath;
     SearchPath searchPath;
     SearchPath::iterator searchPathInsertionPoint;
-- 
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