module: cache stat() results more aggressively

lib/fs.js

@@ -1550,7 +1550,7 @@ fs.realpathSync = function realpathSync(p, cache) {
         }
       }
       if (linkTarget === null) {
-        fs.statSync(base);
+        fs.accessSync(base, fs.F_OK);  // Throws ELOOP on cyclic links.
         linkTarget = fs.readlinkSync(base);
       }
       resolvedLink = pathModule.resolve(previous, linkTarget);

lib/internal/module.js

@@ -1,6 +1,8 @@
 'use strict';
 
-module.exports = { makeRequireFunction, stripBOM };
+exports = module.exports = { makeRequireFunction, stripBOM };
+
+exports.requireDepth = 0;
 
 // Invoke with makeRequireFunction.call(module) where |module| is the
 // Module object to use as the context for the require() function.
@@ -9,7 +11,12 @@ function makeRequireFunction() {
   const self = this;
 
   function require(path) {
-    return self.require(path);
+    try {
+      exports.requireDepth += 1;
+      return self.require(path);
+    } finally {
+      exports.requireDepth -= 1;
+    }
   }
 
   require.resolve = function(request) {

lib/module.js

@@ -33,6 +33,20 @@ function tryWrapper(wrapper, opts) {
 }
 
 
+function stat(filename) {
+  filename = path._makeLong(filename);
+  const cache = stat.cache;
+  if (cache !== null) {
+    const result = cache.get(filename);
+    if (result !== undefined) return result;
+  }
+  const result = internalModuleStat(filename);
+  if (cache !== null) cache.set(filename, result);
+  return result;
+}
+stat.cache = null;
+
+
 function Module(id, parent) {
   this.id = id;
   this.exports = {};
@@ -114,7 +128,7 @@ Module._realpathCache = {};
 
 // check if the file exists and is not a directory
 function tryFile(requestPath) {
-  const rc = internalModuleStat(path._makeLong(requestPath));
+  const rc = stat(requestPath);
   return rc === 0 && toRealPath(requestPath);
 }
 
@@ -152,12 +166,12 @@ Module._findPath = function(request, paths) {
   // For each path
   for (var i = 0, PL = paths.length; i < PL; i++) {
     // Don't search further if path doesn't exist
-    if (paths[i] && internalModuleStat(path._makeLong(paths[i])) < 1) continue;
+    if (paths[i] && stat(paths[i]) < 1) continue;
     var basePath = path.resolve(paths[i], request);
     var filename;
 
     if (!trailingSlash) {
-      const rc = internalModuleStat(path._makeLong(basePath));
+      const rc = stat(basePath);
       if (rc === 0) {  // File.
         filename = toRealPath(basePath);
       } else if (rc === 1) {  // Directory.
@@ -361,7 +375,7 @@ Module.prototype.load = function(filename) {
 Module.prototype.require = function(path) {
   assert(path, 'missing path');
   assert(typeof path === 'string', 'path must be a string');
-  return Module._load(path, this);
+  return Module._load(path, this, /* isMain */ false);
 };
 
 
@@ -405,20 +419,24 @@ Module.prototype._compile = function(content, filename) {
   const dirname = path.dirname(filename);
   const require = internalModule.makeRequireFunction.call(this);
   const args = [this.exports, require, this, filename, dirname];
-  return compiledWrapper.apply(this.exports, args);
+  const depth = internalModule.requireDepth;
+  if (depth === 0) stat.cache = new Map();
+  const result = compiledWrapper.apply(this.exports, args);
+  if (depth === 0) stat.cache = null;
+  return result;
 };
 
 
 // Native extension for .js
 Module._extensions['.js'] = function(module, filename) {
-  var content = fs.readFileSync(filename, 'utf8');
+  var content = internalModuleReadFile(filename);
   module._compile(internalModule.stripBOM(content), filename);
 };
 
 
 // Native extension for .json
 Module._extensions['.json'] = function(module, filename) {
-  var content = fs.readFileSync(filename, 'utf8');
+  var content = internalModuleReadFile(filename);
   try {
     module.exports = JSON.parse(internalModule.stripBOM(content));
   } catch (err) {

test/fixtures/module-require-depth/one.js

@@ -0,0 +1,9 @@
+// Flags: --expose_internals
+'use strict';
+const assert = require('assert');
+const internalModule = require('internal/module');
+
+exports.requireDepth = internalModule.requireDepth;
+assert.strictEqual(internalModule.requireDepth, 1);
+assert.deepStrictEqual(require('./two'), { requireDepth: 2 });
+assert.strictEqual(internalModule.requireDepth, 1);

test/fixtures/module-require-depth/two.js

@@ -0,0 +1,9 @@
+// Flags: --expose_internals
+'use strict';
+const assert = require('assert');
+const internalModule = require('internal/module');
+
+exports.requireDepth = internalModule.requireDepth;
+assert.strictEqual(internalModule.requireDepth, 2);
+assert.deepStrictEqual(require('./one'), { requireDepth: 1 });
+assert.strictEqual(internalModule.requireDepth, 2);

test/parallel/test-module-require-depth.js

@@ -0,0 +1,13 @@
+// Flags: --expose_internals
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const internalModule = require('internal/module');
+
+// Module one loads two too so the expected depth for two is, well, two.
+assert.strictEqual(internalModule.requireDepth, 0);
+const one = require(common.fixturesDir + '/module-require-depth/one');
+const two = require(common.fixturesDir + '/module-require-depth/two');
+assert.deepStrictEqual(one, { requireDepth: 1 });
+assert.deepStrictEqual(two, { requireDepth: 2 });
+assert.strictEqual(internalModule.requireDepth, 0);