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, 26 insertions, 1 deletions

diff --git a/lib/internal/fs/dir.js b/lib/internal/fs/dir.js
index 175c632fc7..fedd7ff8ed 100644
--- a/lib/internal/fs/dir.js
+++ b/lib/internal/fs/dir.js
@@ -24,8 +24,10 @@ const {
 
 const kDirHandle = Symbol('kDirHandle');
 const kDirPath = Symbol('kDirPath');
+const kDirBufferedEntries = Symbol('kDirBufferedEntries');
 const kDirClosed = Symbol('kDirClosed');
 const kDirOptions = Symbol('kDirOptions');
+const kDirReadImpl = Symbol('kDirReadImpl');
 const kDirReadPromisified = Symbol('kDirReadPromisified');
 const kDirClosePromisified = Symbol('kDirClosePromisified');
 
@@ -33,6 +35,7 @@ class Dir {
   constructor(handle, path, options) {
     if (handle == null) throw new ERR_MISSING_ARGS('handle');
     this[kDirHandle] = handle;
+    this[kDirBufferedEntries] = [];
     this[kDirPath] = path;
     this[kDirClosed] = false;
 
@@ -40,7 +43,8 @@ class Dir {
       encoding: 'utf8'
     });
 
-    this[kDirReadPromisified] = internalUtil.promisify(this.read).bind(this);
+    this[kDirReadPromisified] =
+        internalUtil.promisify(this[kDirReadImpl]).bind(this, false);
     this[kDirClosePromisified] = internalUtil.promisify(this.close).bind(this);
   }
 
@@ -49,6 +53,10 @@ class Dir {
   }
 
   read(callback) {
+    return this[kDirReadImpl](true, callback);
+  }
+
+  [kDirReadImpl](maybeSync, callback) {
     if (this[kDirClosed] === true) {
       throw new ERR_DIR_CLOSED();
     }
@@ -59,11 +67,22 @@ class Dir {
       throw new ERR_INVALID_CALLBACK(callback);
     }
 
+    if (this[kDirBufferedEntries].length > 0) {
+      const [ name, type ] = this[kDirBufferedEntries].splice(0, 2);
+      if (maybeSync)
+        process.nextTick(getDirent, this[kDirPath], name, type, callback);
+      else
+        getDirent(this[kDirPath], name, type, callback);
+      return;
+    }
+
     const req = new FSReqCallback();
     req.oncomplete = (err, result) => {
       if (err || result === null) {
         return callback(err, result);
       }
+
+      this[kDirBufferedEntries] = result.slice(2);
       getDirent(this[kDirPath], result[0], result[1], callback);
     };
 
@@ -78,6 +97,11 @@ class Dir {
       throw new ERR_DIR_CLOSED();
     }
 
+    if (this[kDirBufferedEntries].length > 0) {
+      const [ name, type ] = this[kDirBufferedEntries].splice(0, 2);
+      return getDirent(this[kDirPath], name, type);
+    }
+
     const ctx = { path: this[kDirPath] };
     const result = this[kDirHandle].read(
       this[kDirOptions].encoding,
@@ -90,6 +114,7 @@ class Dir {
       return result;
     }
 
+    this[kDirBufferedEntries] = result.slice(2);
     return getDirent(this[kDirPath], result[0], result[1]);
   }