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module: significantly improve loader performance #26970

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b5683e7
benchmark: add new module loading benchmarks
BridgeAR Jan 2, 2019
faa0518
benchmark: improve module-loader benchmark
BridgeAR Mar 28, 2019
50e2414
module: inline try catch
BridgeAR Mar 28, 2019
538f745
module: add path to the module object
BridgeAR Mar 28, 2019
9137c56
module: add extra caching layer
BridgeAR Mar 28, 2019
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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.
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@BridgeAR
BridgeAR committed Mar 31, 2019
commit 9137c56963bee921273522dc91e6c7dd90cbaafa
24 changes: 23 additions & 1 deletion lib/internal/modules/cjs/loader.js
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,8 @@ const {

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

const relativeResolveCache = Object.create(null);

let requireDepth = 0;
let statCache = new Map();
function stat(filename) {
Expand Down Expand Up @@ -598,14 +600,28 @@ 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;
}
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@jdalton jdalton Mar 29, 2019

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Could this be done at the Module._resolveFilename level?
A cache key could be something like

cacheKey =
  request + "\0" +
  dirPath + "\0" +
  (isMain ? "1" : "")

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@BridgeAR BridgeAR Mar 31, 2019

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That would not be beneficial as far as I can tell. I would also rather not move any parts around since the loader is highly monkey patched and every subtle change can cause side-effects.

isMain should not have any impact on the key as it's only about the very first require call and that is not required for the cache key.

Expand All @@ -625,6 +641,9 @@ Module._load = function(request, parent, isMain) {
}

Module._cache[filename] = module;
if (parent !== undefined) {
relativeResolveCache[relResolveCacheIdentifier] = filename;
}

let threw = true;
try {
Expand All @@ -633,6 +652,9 @@ Module._load = function(request, parent, isMain) {
} finally {
if (threw) {
delete Module._cache[filename];
if (parent !== undefined) {
delete relativeResolveCache[relResolveCacheIdentifier];
}
}
}

Expand Down