Skip to content

module: cache negative stat results in the CJS loader #64682

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
maxday wants to merge 1 commit into
base: main
Choose a base branch
from
+44 −2
Open

module: cache negative stat results in the CJS loader #64682

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
12 changes: 10 additions & 2 deletions lib/internal/modules/cjs/loader.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -279,8 +279,16 @@ function stat(filename) {
if (result !== undefined) { return result; }
}
const result = internalFsBinding.internalModuleStat(filename);
if (statCache !== null && result >= 0) {
// Only set cache when `internalModuleStat(filename)` succeeds.
if (statCache !== null) {
// Cache both successful results (0 = file, 1 = directory) and negative
// results (libuv error codes, e.g. -ENOENT). Negative results are common
// and repeated during resolution: `tryExtensions` probes several
// non-existent extensions, and bare specifiers walk the `node_modules`
// chain upward stat-ing many parent directories that do not exist. The
// cache is scoped to a single top-level `require` tree (created and torn
// down around `requireDepth === 0`), so caching a negative result carries
// the same bounded staleness window that caching a positive one already
// does.
statCache.set(filename, result);
}
return result;
Expand Down
34 changes: 34 additions & 0 deletions test/parallel/test-module-negative-stat-cache.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
'use strict';
require('../common');

// This tests that the CommonJS loader's per-require-tree stat cache also caches
// negative (not-found) results, so a path that is missing when first probed is
// not re-stat-ed for the rest of the require tree.

const assert = require('assert');
const fs = require('fs');
const tmpdir = require('../common/tmpdir');

tmpdir.refresh();

// A module path that does not exist yet.
const generated = tmpdir.resolve('generated.js');

// First probe: the file does not exist -> negative stat, cached.
assert.throws(
() => require(generated),
{ code: 'MODULE_NOT_FOUND' },
'expected the module to be missing before it is created',
);

// Create the file mid-traversal, in the same require tree.
fs.writeFileSync(generated, 'module.exports = 1;');

// Second probe, still in the same tree: the negative result is cached, so the
// loader must serve the cached miss instead of re-stat-ing and observing the
// freshly-created file.
assert.throws(
() => require(generated),
{ code: 'MODULE_NOT_FOUND' },
'a negative stat result must be cached for the rest of the require tree',
);
Loading