fs: buffer dir entries in opendir()

Read up to 32 directory entries in one batch when `dir.readSync()`
or `dir.read()` are called.

This increases performance significantly, although it introduces
quite a bit of edge case complexity.

                                                                 confidence improvement accuracy (*)    (**)    (***)
     fs/bench-opendir.js mode='async' dir='lib' n=100                  ***    155.93 %      ±30.05% ±40.34%  ±53.21%
     fs/bench-opendir.js mode='async' dir='test/parallel' n=100        ***    479.65 %      ±56.81% ±76.47% ±101.32%
     fs/bench-opendir.js mode='sync' dir='lib' n=100                           10.38 %      ±14.39% ±19.16%  ±24.96%
     fs/bench-opendir.js mode='sync' dir='test/parallel' n=100         ***     63.13 %      ±12.84% ±17.18%  ±22.58%

PR-URL: https://github.com/nodejs/node/pull/29893
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/benchmark/fs/bench-opendir.js b/benchmark/fs/bench-opendir.js
new file mode 100644
index 0000000000..419c3a231a
--- /dev/null
+++ b/benchmark/fs/bench-opendir.js
@@ -0,0 +1,51 @@
+'use strict';
+
+const common = require('../common');
+const fs = require('fs');
+const path = require('path');
+
+const bench = common.createBenchmark(main, {
+  n: [100],
+  dir: [ 'lib', 'test/parallel'],
+  mode: [ 'async', 'sync', 'callback' ]
+});
+
+async function main({ n, dir, mode }) {
+  const fullPath = path.resolve(__dirname, '../../', dir);
+
+  bench.start();
+
+  let counter = 0;
+  for (let i = 0; i < n; i++) {
+    if (mode === 'async') {
+      // eslint-disable-next-line no-unused-vars
+      for await (const entry of await fs.promises.opendir(fullPath))
+        counter++;
+    } else if (mode === 'callback') {
+      const dir = await fs.promises.opendir(fullPath);
+      await new Promise((resolve, reject) => {
+        function read() {
+          dir.read((err, entry) => {
+            if (err) {
+              reject(err);
+            } else if (entry === null) {
+              resolve(dir.close());
+            } else {
+              counter++;
+              read();
+            }
+          });
+        }
+
+        read();
+      });
+    } else {
+      const dir = fs.opendirSync(fullPath);
+      while (dir.readSync() !== null)
+        counter++;
+      dir.closeSync();
+    }
+  }
+
+  bench.end(counter);
+}