From 2205f85b2caadee425a0a86bd8cc3bcb889e4bfe Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Fri, 29 Nov 2019 02:04:46 +0100
Subject: [PATCH] stream: improve performance for sync write finishes
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Improve performance and reduce memory usage when a writable stream
is written to with the same callback (which is the most common case)
and when the write operation finishes synchronously (which is also
often the case).

                                                         confidence improvement accuracy (*)    (**)   (***)
    streams/writable-manywrites.js sync='no' n=2000000                  0.99 %       ±3.20%  ±4.28%  ±5.61%
    streams/writable-manywrites.js sync='yes' n=2000000        ***    710.69 %      ±19.65% ±26.47% ±35.09%

Refs: https://github.com/nodejs/node/issues/18013
Refs: https://github.com/nodejs/node/issues/18367

PR-URL: https://github.com/nodejs/node/pull/30710
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 benchmark/streams/writable-manywrites.js      | 11 +++++--
 lib/_stream_writable.js                       | 33 ++++++++++++++++---
 .../test-stream-writable-samecb-singletick.js | 30 +++++++++++++++++
 3 files changed, 66 insertions(+), 8 deletions(-)
 create mode 100644 test/parallel/test-stream-writable-samecb-singletick.js

diff --git a/benchmark/streams/writable-manywrites.js b/benchmark/streams/writable-manywrites.js
index 6fcb07e849d..0ed38d0357a 100644
--- a/benchmark/streams/writable-manywrites.js
+++ b/benchmark/streams/writable-manywrites.js
@@ -4,14 +4,19 @@ const common = require('../common');
 const Writable = require('stream').Writable;
 
 const bench = common.createBenchmark(main, {
-  n: [2e6]
+  n: [2e6],
+  sync: ['yes', 'no']
 });
 
-function main({ n }) {
+function main({ n, sync }) {
   const b = Buffer.allocUnsafe(1024);
   const s = new Writable();
+  sync = sync === 'yes';
   s._write = function(chunk, encoding, cb) {
-    cb();
+    if (sync)
+      cb();
+    else
+      process.nextTick(cb);
   };
 
   bench.start();
diff --git a/lib/_stream_writable.js b/lib/_stream_writable.js
index cf498e7d93c..ab168fafe51 100644
--- a/lib/_stream_writable.js
+++ b/lib/_stream_writable.js
@@ -142,6 +142,10 @@ function WritableState(options, stream, isDuplex) {
   // The amount that is being written when _write is called.
   this.writelen = 0;
 
+  // Storage for data passed to the afterWrite() callback in case of
+  // synchronous _write() completion.
+  this.afterWriteTickInfo = null;
+
   this.bufferedRequest = null;
   this.lastBufferedRequest = null;
 
@@ -498,22 +502,41 @@ function onwrite(stream, er) {
     }
 
     if (sync) {
-      process.nextTick(afterWrite, stream, state, cb);
+      // It is a common case that the callback passed to .write() is always
+      // the same. In that case, we do not schedule a new nextTick(), but rather
+      // just increase a counter, to improve performance and avoid memory
+      // allocations.
+      if (state.afterWriteTickInfo !== null &&
+          state.afterWriteTickInfo.cb === cb) {
+        state.afterWriteTickInfo.count++;
+      } else {
+        state.afterWriteTickInfo = { count: 1, cb, stream, state };
+        process.nextTick(afterWriteTick, state.afterWriteTickInfo);
+      }
     } else {
-      afterWrite(stream, state, cb);
+      afterWrite(stream, state, 1, cb);
     }
   }
 }
 
-function afterWrite(stream, state, cb) {
+function afterWriteTick({ stream, state, count, cb }) {
+  state.afterWriteTickInfo = null;
+  return afterWrite(stream, state, count, cb);
+}
+
+function afterWrite(stream, state, count, cb) {
   const needDrain = !state.ending && !stream.destroyed && state.length === 0 &&
     state.needDrain;
   if (needDrain) {
     state.needDrain = false;
     stream.emit('drain');
   }
-  state.pendingcb--;
-  cb();
+
+  while (count-- > 0) {
+    state.pendingcb--;
+    cb();
+  }
+
   finishMaybe(stream, state);
 }
 
diff --git a/test/parallel/test-stream-writable-samecb-singletick.js b/test/parallel/test-stream-writable-samecb-singletick.js
new file mode 100644
index 00000000000..e7dfa648797
--- /dev/null
+++ b/test/parallel/test-stream-writable-samecb-singletick.js
@@ -0,0 +1,30 @@
+'use strict';
+const common = require('../common');
+const { Console } = require('console');
+const { Writable } = require('stream');
+const async_hooks = require('async_hooks');
+
+// Make sure that repeated calls to console.log(), and by extension
+// stream.write() for the underlying stream, allocate exactly 1 tick object.
+// At the time of writing, that is enough to ensure a flat memory profile
+// from repeated console.log() calls, rather than having callbacks pile up
+// over time, assuming that data can be written synchronously.
+// Refs: https://github.com/nodejs/node/issues/18013
+// Refs: https://github.com/nodejs/node/issues/18367
+
+const checkTickCreated = common.mustCall();
+
+async_hooks.createHook({
+  init(id, type, triggerId, resoure) {
+    if (type === 'TickObject') checkTickCreated();
+  }
+}).enable();
+
+const console = new Console(new Writable({
+  write: common.mustCall((chunk, encoding, cb) => {
+    cb();
+  }, 100)
+}));
+
+for (let i = 0; i < 100; i++)
+  console.log(i);