modules: significantly improve require performance

benchmark/module/load-native.js

@@ -0,0 +1,19 @@
+'use strict';
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  path: ['vm', 'util'],
+  n: [1000],
+  useCache: ['true', 'false']
+});
+
+function main({ n, path, useCache }) {
+  if (useCache)
+    require(path);
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    require(path);
+  }
+  bench.end(n);
+}

benchmark/module/module-loader-deep.js

@@ -0,0 +1,51 @@
+'use strict';
+const fs = require('fs');
+const path = require('path');
+const common = require('../common.js');
+
+const tmpdir = require('../../test/common/tmpdir');
+const benchmarkDirectory = path.join(tmpdir.path, 'nodejs-benchmark-module');
+
+const bench = common.createBenchmark(main, {
+  ext: ['', '.js'],
+  files: [1e3],
+  cache: ['true', 'false']
+});
+
+function main({ ext, cache, files }) {
+  tmpdir.refresh();
+  fs.mkdirSync(benchmarkDirectory);
+  fs.writeFileSync(
+    `${benchmarkDirectory}/a.js`,
+    'module.exports = {};'
+  );
+  for (var i = 0; i <= files; i++) {
+    fs.mkdirSync(`${benchmarkDirectory}/${i}`);
+    fs.writeFileSync(
+      `${benchmarkDirectory}/${i}/package.json`,
+      '{"main": "index.js"}'
+    );
+    fs.writeFileSync(
+      `${benchmarkDirectory}/${i}/index.js`,
+      `require('../a${ext}');`
+    );
+  }
+
+  measureDir(cache === 'true', files);
+
+  tmpdir.refresh();
+}
+
+function measureDir(cache, files) {
+  var i;
+  if (cache) {
+    for (i = 0; i <= files; i++) {
+      require(`${benchmarkDirectory}/${i}`);
+    }
+  }
+  bench.start();
+  for (i = 0; i <= files; i++) {
+    require(`${benchmarkDirectory}/${i}`);
+  }
+  bench.end(files);
+}

benchmark/module/module-loader.js

@@ -4,18 +4,20 @@ const path = require('path');
 const common = require('../common.js');
 
 const tmpdir = require('../../test/common/tmpdir');
-const benchmarkDirectory = path.join(tmpdir.path, 'nodejs-benchmark-module');
+let benchmarkDirectory = path.join(tmpdir.path, 'nodejs-benchmark-module');
 
 const bench = common.createBenchmark(main, {
-  n: [5e4],
-  fullPath: ['true', 'false'],
-  useCache: ['true', 'false']
+  name: ['', '/', '/index.js'],
+  dir: ['rel', 'abs'],
+  files: [5e2],
+  n: [1, 1e3],
+  cache: ['true', 'false']
 });
 
-function main({ n, fullPath, useCache }) {
+function main({ n, name, cache, files, dir }) {
   tmpdir.refresh();
-  try { fs.mkdirSync(benchmarkDirectory); } catch {}
-  for (var i = 0; i <= n; i++) {
+  fs.mkdirSync(benchmarkDirectory);
+  for (var i = 0; i <= files; i++) {
     fs.mkdirSync(`${benchmarkDirectory}${i}`);
     fs.writeFileSync(
       `${benchmarkDirectory}${i}/package.json`,
@@ -27,38 +29,25 @@ function main({ n, fullPath, useCache }) {
     );
   }
 
-  if (fullPath === 'true')
-    measureFull(n, useCache === 'true');
-  else
-    measureDir(n, useCache === 'true');
+  if (dir === 'rel')
+    benchmarkDirectory = path.relative(__dirname, benchmarkDirectory);
 
-  tmpdir.refresh();
-}
+  measureDir(n, cache === 'true', files, name);
 
-function measureFull(n, useCache) {
-  var i;
-  if (useCache) {
-    for (i = 0; i <= n; i++) {
-      require(`${benchmarkDirectory}${i}/index.js`);
-    }
-  }
-  bench.start();
-  for (i = 0; i <= n; i++) {
-    require(`${benchmarkDirectory}${i}/index.js`);
-  }
-  bench.end(n);
+  tmpdir.refresh();
 }
 
-function measureDir(n, useCache) {
+function measureDir(n, cache, files, name) {
   var i;
-  if (useCache) {
-    for (i = 0; i <= n; i++) {
-      require(`${benchmarkDirectory}${i}`);
+  if (cache) {
+    for (i = 0; i <= files; i++) {
+      require(`${benchmarkDirectory}${i}${name}`);
     }
   }
   bench.start();
-  for (i = 0; i <= n; i++) {
-    require(`${benchmarkDirectory}${i}`);
+  for (i = 0; i <= files; i++) {
+    for (var j = 0; j < n; j++)
+      require(`${benchmarkDirectory}${i}${name}`);
   }
-  bench.end(n);
+  bench.end(n * files);
 }

doc/api/deprecations.md

@@ -442,6 +442,9 @@ code.
 ### DEP0019: require('.') resolved outside directory
 <!-- YAML
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/REPLACEME
+    description: Removed functionality.
   - version:
     - v4.8.6
     - v6.12.0
@@ -452,11 +455,10 @@ changes:
     description: Runtime deprecation.
 -->
 
-Type: Runtime
+Type: End-of-Life
 
-In certain cases, `require('.')` may resolve outside the package directory.
-This behavior is deprecated and will be removed in a future major Node.js
-release.
+In certain cases, `require('.')` could resolve outside the package directory.
+This behavior has been removed.
 
 <a id="DEP0020"></a>
 ### DEP0020: Server.connections

doc/api/modules.md

@@ -196,28 +196,26 @@ NODE_MODULES_PATHS(START)
 
 <!--type=misc-->
 
-Modules are cached after the first time they are loaded. This means
-(among other things) that every call to `require('foo')` will get
-exactly the same object returned, if it would resolve to the same file.
+Modules are cached after the first time they are loaded. This means (among other
+things) that every call to `require('foo')` will get exactly the same object
+returned, if it would resolve to the same file.
 
-Provided `require.cache` is not modified, multiple calls to
-`require('foo')` will not cause the module code to be executed multiple times.
-This is an important feature. With it, "partially done" objects can be returned,
-thus allowing transitive dependencies to be loaded even when they would cause
-cycles.
+Provided `require.cache` is not modified, multiple calls to `require('foo')`
+will not cause the module code to be executed multiple times. This is an
+important feature. With it, "partially done" objects can be returned, thus
+allowing transitive dependencies to be loaded even when they would cause cycles.
 
-To have a module execute code multiple times, export a function, and call
-that function.
+To have a module execute code multiple times, export a function, and call that
+function.
 
 ### Module Caching Caveats
 
 <!--type=misc-->
 
-Modules are cached based on their resolved filename. Since modules may
-resolve to a different filename based on the location of the calling
-module (loading from `node_modules` folders), it is not a *guarantee*
-that `require('foo')` will always return the exact same object, if it
-would resolve to different files.
+Modules are cached based on their resolved filename. Since modules may resolve
+to a different filename based on the location of the calling module (loading
+from `node_modules` folders), it is not a *guarantee* that `require('foo')` will
+always return the exact same object, if it would resolve to different files.
 
 Additionally, on case-insensitive file systems or operating systems, different
 resolved filenames can point to the same file, but the cache will still treat
@@ -412,7 +410,7 @@ are not found elsewhere.
 On Windows, `NODE_PATH` is delimited by semicolons (`;`) instead of colons.
 
 `NODE_PATH` was originally created to support loading modules from
-varying paths before the current [module resolution][] algorithm was frozen.
+varying paths before the current [module resolution][] algorithm was defined.
 
 `NODE_PATH` is still supported, but is less necessary now that the Node.js
 ecosystem has settled on a convention for locating dependent modules.
@@ -582,6 +580,10 @@ value from this object, the next `require` will reload the module. Note that
 this does not apply to [native addons][], for which reloading will result in an
 error.
 
+Adding ore replacing entries is also possible. This cache is checked before
+native modules and if such a name is added to the cache, no require call is
+going to receive the native module anymore. Use with care!
+
 #### require.extensions
 <!-- YAML
 added: v0.3.0
@@ -600,22 +602,15 @@ Process files with the extension `.sjs` as `.js`:
 require.extensions['.sjs'] = require.extensions['.js'];
 ```
 
-**Deprecated** In the past, this list has been used to load
-non-JavaScript modules into Node.js by compiling them on-demand.
-However, in practice, there are much better ways to do this, such as
-loading modules via some other Node.js program, or compiling them to
-JavaScript ahead of time.
-
-Since the module system is locked, this feature will probably never go
-away. However, it may have subtle bugs and complexities that are best
-left untouched.
-
-Note that the number of file system operations that the module system
-has to perform in order to resolve a `require(...)` statement to a
-filename scales linearly with the number of registered extensions.
+**Deprecated** In the past, this list has been used to load non-JavaScript
+modules into Node.js by compiling them on-demand. However, in practice, there
+are much better ways to do this, such as loading modules via some other Node.js
+program, or compiling them to JavaScript ahead of time.
 
-In other words, adding extensions slows down the module loader and
-should be discouraged.
+Using this could cause subtle bugs and adding extensions slows down the module
+loader and is therefore discouraged (the number of file system operations that
+the module system has to perform in order to resolve a `require(...)` statement
+to a filename scales linearly with the number of registered extensions).
 
 #### require.main
 <!-- YAML

lib/internal/bootstrap/loaders.js

@@ -179,21 +179,33 @@ NativeModule._cache = {};
 
 const config = internalBinding('config');
 
+// Do not expose this to user land even with --expose-internals.
+const loaderId = 'internal/bootstrap/loaders';
+
+// Create a native module map to tell if a module is internal or not.
+const moduleState = {};
+const moduleNames = Object.keys(source);
+for (const name of moduleNames) {
+  moduleState[name] = name === loaderId ||
+    !config.exposeInternals &&
+    (name.startsWith('internal/') ||
+      (name === 'worker_threads' && !config.experimentalWorker));
+}
+
 // Think of this as module.exports in this file even though it is not
 // written in CommonJS style.
 const loaderExports = { internalBinding, NativeModule };
-const loaderId = 'internal/bootstrap/loaders';
 
 NativeModule.require = function(id) {
-  if (id === loaderId) {
-    return loaderExports;
-  }
-
   const cached = NativeModule.getCached(id);
-  if (cached && (cached.loaded || cached.loading)) {
+  if (cached !== undefined && (cached.loaded || cached.loading)) {
     return cached.exports;
   }
 
+  if (id === loaderId) {
+    return loaderExports;
+  }
+
   if (!NativeModule.exists(id)) {
     // Model the error off the internal/errors.js model, but
     // do not use that module given that it could actually be
@@ -231,32 +243,16 @@ NativeModule.getCached = function(id) {
 };
 
 NativeModule.exists = function(id) {
-  return NativeModule._source.hasOwnProperty(id);
+  return NativeModule._source[id] !== undefined;
 };
 
-if (config.exposeInternals) {
-  NativeModule.nonInternalExists = function(id) {
-    // Do not expose this to user land even with --expose-internals.
-    if (id === loaderId) {
-      return false;
-    }
-    return NativeModule.exists(id);
-  };
-
-  NativeModule.isInternal = function(id) {
-    // Do not expose this to user land even with --expose-internals.
-    return id === loaderId;
-  };
-} else {
-  NativeModule.nonInternalExists = function(id) {
-    return NativeModule.exists(id) && !NativeModule.isInternal(id);
-  };
+NativeModule.nonInternalExists = function(id) {
+  return NativeModule.exists(id) && !NativeModule.isInternal(id);
+};
 
-  NativeModule.isInternal = function(id) {
-    return id.startsWith('internal/') ||
-        (id === 'worker_threads' && !config.experimentalWorker);
-  };
-}
+NativeModule.isInternal = function(id) {
+  return moduleState[id];
+};
 
 NativeModule.getSource = function(id) {
   return NativeModule._source[id];