From 5917f4d49b8eda431208619abb20fadd371f2897 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Thu, 28 Mar 2019 23:37:07 +0100
Subject: [PATCH] module: add extra caching layer

This adds an extra modules caching layer that operates on the parent's
`path` property and the current require argument. That together can
be used as unique identifier to speed up loading the same module more
than once. It is a cache on top of the current modules cache.

It has the nice feature that this cache does not only work in the same
file but it works for the whole current directory. So if the same file
is loaded in any other file from the same directory, it will also hit
this cache instead of having to resolve the file again.

To keep it backwards compatible with the old modules cache, it detects
invalidation of that cache.

PR-URL: https://github.com/nodejs/node/pull/26970
Refs: https://github.com/nodejs/node/pull/25362
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Signed-off-by: Beth Griggs <Bethany.Griggs@uk.ibm.com>
---
 lib/internal/modules/cjs/loader.js | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index b8eed4b808a965..de97f03dd47abe 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -77,6 +77,8 @@ const {
 
 const isWindows = process.platform === 'win32';
 
+const relativeResolveCache = Object.create(null);
+
 let requireDepth = 0;
 let statCache = null;
 function stat(filename) {
@@ -568,14 +570,28 @@ Module._resolveLookupPaths = function(request, parent, newReturn) {
 //    Then have it load  the file contents before returning its exports
 //    object.
 Module._load = function(request, parent, isMain) {
+  let relResolveCacheIdentifier;
   if (parent) {
     debug('Module._load REQUEST %s parent: %s', request, parent.id);
+    // Fast path for (lazy loaded) modules in the same directory. The indirect
+    // caching is required to allow cache invalidation without changing the old
+    // cache key names.
+    relResolveCacheIdentifier = `${parent.path}\x00${request}`;
+    const filename = relativeResolveCache[relResolveCacheIdentifier];
+    if (filename !== undefined) {
+      const cachedModule = Module._cache[filename];
+      if (cachedModule !== undefined) {
+        updateChildren(parent, cachedModule, true);
+        return cachedModule.exports;
+      }
+      delete relativeResolveCache[relResolveCacheIdentifier];
+    }
   }
 
   const filename = Module._resolveFilename(request, parent, isMain);
 
   const cachedModule = Module._cache[filename];
-  if (cachedModule) {
+  if (cachedModule !== undefined) {
     updateChildren(parent, cachedModule, true);
     return cachedModule.exports;
   }
@@ -595,6 +611,9 @@ Module._load = function(request, parent, isMain) {
   }
 
   Module._cache[filename] = module;
+  if (parent !== undefined) {
+    relativeResolveCache[relResolveCacheIdentifier] = filename;
+  }
 
   let threw = true;
   try {
@@ -603,6 +622,9 @@ Module._load = function(request, parent, isMain) {
   } finally {
     if (threw) {
       delete Module._cache[filename];
+      if (parent !== undefined) {
+        delete relativeResolveCache[relResolveCacheIdentifier];
+      }
     }
   }