stream: improve Transform performance

PR-URL: https://github.com/nodejs/node/pull/13322
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

benchmark/streams/transform-creation.js

@@ -0,0 +1,23 @@
+'use strict';
+var common = require('../common.js');
+var Transform = require('stream').Transform;
+var inherits = require('util').inherits;
+
+var bench = common.createBenchmark(main, {
+  n: [1e6]
+});
+
+function MyTransform() {
+  Transform.call(this);
+}
+inherits(MyTransform, Transform);
+MyTransform.prototype._transform = function() {};
+
+function main(conf) {
+  var n = +conf.n;
+
+  bench.start();
+  for (var i = 0; i < n; ++i)
+    new MyTransform();
+  bench.end(n);
+}

lib/_stream_transform.js

@@ -70,41 +70,29 @@ const util = require('util');
 util.inherits(Transform, Duplex);
 
 
-function TransformState(stream) {
-  this.afterTransform = function(er, data) {
-    return afterTransform(stream, er, data);
-  };
-
-  this.needTransform = false;
-  this.transforming = false;
-  this.writecb = null;
-  this.writechunk = null;
-  this.writeencoding = null;
-}
-
-function afterTransform(stream, er, data) {
-  var ts = stream._transformState;
+function afterTransform(er, data) {
+  var ts = this._transformState;
   ts.transforming = false;
 
   var cb = ts.writecb;
 
   if (!cb) {
-    return stream.emit('error',
-                       new Error('write callback called multiple times'));
+    return this.emit('error',
+                     new Error('write callback called multiple times'));
   }
 
   ts.writechunk = null;
   ts.writecb = null;
 
-  if (data !== null && data !== undefined)
-    stream.push(data);
+  if (data != null) // single equals check for both `null` and `undefined`
+    this.push(data);
 
   cb(er);
 
-  var rs = stream._readableState;
+  var rs = this._readableState;
   rs.reading = false;
   if (rs.needReadable || rs.length < rs.highWaterMark) {
-    stream._read(rs.highWaterMark);
+    this._read(rs.highWaterMark);
   }
 }
 
@@ -115,9 +103,14 @@ function Transform(options) {
 
   Duplex.call(this, options);
 
-  this._transformState = new TransformState(this);
-
-  var stream = this;
+  this._transformState = {
+    afterTransform: afterTransform.bind(this),
+    needTransform: false,
+    transforming: false,
+    writecb: null,
+    writechunk: null,
+    writeencoding: null
+  };
 
   // start out asking for a readable event once data is transformed.
   this._readableState.needReadable = true;
@@ -136,14 +129,17 @@ function Transform(options) {
   }
 
   // When the writable side finishes, then flush out anything remaining.
-  this.once('prefinish', function() {
-    if (typeof this._flush === 'function')
-      this._flush(function(er, data) {
-        done(stream, er, data);
-      });
-    else
-      done(stream);
-  });
+  this.on('prefinish', prefinish);
+}
+
+function prefinish() {
+  if (typeof this._flush === 'function') {
+    this._flush((er, data) => {
+      done(this, er, data);
+    });
+  } else {
+    done(this, null, null);
+  }
 }
 
 Transform.prototype.push = function(chunk, encoding) {
@@ -208,18 +204,15 @@ function done(stream, er, data) {
   if (er)
     return stream.emit('error', er);
 
-  if (data !== null && data !== undefined)
+  if (data != null) // single equals check for both `null` and `undefined`
     stream.push(data);
 
   // if there's nothing in the write buffer, then that means
   // that nothing more will ever be provided
-  var ws = stream._writableState;
-  var ts = stream._transformState;
-
-  if (ws.length)
+  if (stream._writableState.length)
     throw new Error('Calling transform done when ws.length != 0');
 
-  if (ts.transforming)
+  if (stream._transformState.transforming)
     throw new Error('Calling transform done when still transforming');
 
   return stream.push(null);