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* Cache the result of file evaluation (i.e, memoize evalFile()). This

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prevents files from being evaluated and stored as values multiple
  times.  For instance, evaluation of the ‘system’ attribute in NixOS
  causes ‘nixpkgs/pkgs/lib/lists.nix’ to be evaluated 2019 times.

  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).
This commit is contained in:
Eelco Dolstra 2011-08-06 19:45:43 +00:00
parent 510033e783
commit 2d663b502d
2 changed files with 22 additions and 11 deletions
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24
src/libexpr/eval.cc
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@ -431,17 +431,19 @@ Value * EvalState::maybeThunk(Env & env, Expr * expr)
void EvalState::evalFile(const Path & path, Value & v)
{
startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
Expr * e = parseExprFromFile(path);
try {
/* !!! Maybe we should cache the evaluation result. */
eval(e, v);
} catch (Error & e) {
addErrorPrefix(e, "while evaluating the file `%1%':\n", path);
throw;
}
FileEvalCache::iterator i = fileEvalCache.find(path);
if (i == fileEvalCache.end()) {
startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
Expr * e = parseExprFromFile(path);
try {
eval(e, v);
} catch (Error & e) {
addErrorPrefix(e, "while evaluating the file `%1%':\n", path);
throw;
}
fileEvalCache[path] = v;
} else
v = i->second;
}

9
src/libexpr/eval.hh
View file

@ -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;