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module: optimize platform lookup and initPath #3582

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module: optimize platform lookup and initPath #3582

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31 changes: 13 additions & 18 deletions lib/module.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ const path = require('path');
const internalModuleReadFile = process.binding('fs').internalModuleReadFile;
const internalModuleStat = process.binding('fs').internalModuleStat;

const isWindows = process.platform === 'win32';

// If obj.hasOwnProperty has been overridden, then calling
// obj.hasOwnProperty(prop) will break.
Expand Down Expand Up @@ -191,7 +192,7 @@ Module._nodeModulePaths = function(from) {
// note: this approach *only* works when the path is guaranteed
// to be absolute. Doing a fully-edge-case-correct path.split
// that works on both Windows and Posix is non-trivial.
var splitRe = process.platform === 'win32' ? /[\/\\]/ : /\//;
var splitRe = isWindows ? /[\/\\]/ : /\//;
var paths = [];
var parts = from.split(splitRe);

Expand Down Expand Up @@ -460,29 +461,23 @@ Module.runMain = function() {
};

Module._initPaths = function() {
const isWindows = process.platform === 'win32';
modulePaths = [];
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Is this necessary?

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Yes. modulePaths is global to this module, and calling _initPaths, resets its value.

node/lib/module.js

Line 485 in 810cc05

modulePaths = paths;

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I'd use modulePaths.length = 0.
That doesn't create a new object which has to be garbage collected

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@meinklaus _initPaths is called only once and modulePaths is undefined at the beginning.

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Looking at https://github.com/zertosh/node/blob/module-improv/lib/module.js#L41 I don't think it is undefined.
If _initPaths is only called once there is no need to assign modulePaths again.

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arr.length = 0 is magical and AFIAK it's not a convention that's used here


if (isWindows) {
var homeDir = process.env.USERPROFILE;
} else {
var homeDir = process.env.HOME;
var nodePath = process.env['NODE_PATH'];
if (nodePath) {
var nodePaths = nodePath.split(path.delimiter);
for (var i = 0; i < nodePaths.length; i++) {
if (nodePaths[i]) modulePaths.push(nodePaths[i]);
}
}

var paths = [path.resolve(process.execPath, '..', '..', 'lib', 'node')];

var homeDir = isWindows ? process.env.USERPROFILE : process.env.HOME;
if (homeDir) {
paths.unshift(path.resolve(homeDir, '.node_libraries'));
paths.unshift(path.resolve(homeDir, '.node_modules'));
}

var nodePath = process.env['NODE_PATH'];
if (nodePath) {
paths = nodePath.split(path.delimiter).filter(function(path) {
return !!path;
}).concat(paths);
modulePaths.push(path.resolve(homeDir, '.node_modules'));
modulePaths.push(path.resolve(homeDir, '.node_libraries'));
}

modulePaths = paths;
modulePaths.push(path.resolve(process.execPath, '..', '..', 'lib', 'node'));

// clone as a read-only copy, for introspection.
Module.globalPaths = modulePaths.slice(0);
Expand Down