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, 12 insertions, 2 deletions

diff --git a/test/parallel/test-fs-opendir.js b/test/parallel/test-fs-opendir.js
index c9a6d657ed..f2c5d03345 100644
--- a/test/parallel/test-fs-opendir.js
+++ b/test/parallel/test-fs-opendir.js
@@ -58,17 +58,27 @@ const dirclosedError = {
 // Check the opendir async version
 fs.opendir(testDir, common.mustCall(function(err, dir) {
   assert.ifError(err);
-  dir.read(common.mustCall(function(err, dirent) {
+  let sync = true;
+  dir.read(common.mustCall((err, dirent) => {
+    assert(!sync);
     assert.ifError(err);
 
     // Order is operating / file system dependent
     assert(files.includes(dirent.name), `'files' should include ${dirent}`);
     assertDirent(dirent);
 
-    dir.close(common.mustCall(function(err) {
+    let syncInner = true;
+    dir.read(common.mustCall((err, dirent) => {
+      assert(!syncInner);
       assert.ifError(err);
+
+      dir.close(common.mustCall(function(err) {
+        assert.ifError(err);
+      }));
     }));
+    syncInner = false;
   }));
+  sync = false;
 }));
 
 // opendir() on file should throw ENOTDIR