Performance - Data batching

app/rpc.js

@@ -34,7 +34,11 @@ class Server extends EventEmitter {
   }
 
   emit(ch, data) {
-    this.wc.send(this.id, {ch, data});
+    // This check is needed because data-batching can cause extra data to be
+    // emitted after the window has already closed
+    if (!this.win.isDestroyed()) {
+      this.wc.send(this.id, {ch, data});
+    }
   }
 
   destroy() {

app/session.js

@@ -21,8 +21,60 @@ try {
 
 const envFromConfig = config.getConfig().env || {};
 
+// Max duration to batch session data before sending it to the renderer process.
+const BATCH_DURATION_MS = 16;
+
+// Max size of a session data batch. Note that this value can be exceeded by ~4k
+// (chunk sizes seem to be 4k at the most)
+const BATCH_MAX_SIZE = 200 * 1024;
+
+// Data coming from the pty is sent to the renderer process for further
+// vt parsing and rendering. This class batches data to minimize the number of
+// IPC calls. It also reduces GC pressure and CPU cost: each chunk is prefixed
+// with the window ID which is then stripped on the renderer process and this
+// overhead is reduced with batching.
+class DataBatcher extends EventEmitter {
+  constructor(uid) {
+    super();
+    this.uid = uid;
+    this.decoder = new StringDecoder('utf8');
+
+    this.reset();
+  }
+
+  reset() {
+    this.data = this.uid;
+    this.timeout = null;
+  }
+
+  write(chunk) {
+    if (this.data.length + chunk.length >= BATCH_MAX_SIZE) {
+      // We've reached the max batch size. Flush it and start another one
+      if (this.timeout) {
+        clearTimeout(this.timeout);
+        this.timeout = null;
+      }
+      this.flush();
+    }
+
+    this.data += this.decoder.write(chunk);
+
+    if (!this.timeout) {
+      this.timeout = setTimeout(() => this.flush(), BATCH_DURATION_MS);
+    }
+  }
+
+  flush() {
+    // Reset before emitting to allow for potential reentrancy
+    const data = this.data;
+    this.reset();
+
+    this.emit('flush', data);
+  }
+}
+
 module.exports = class Session extends EventEmitter {
-  constructor({rows, cols: columns, cwd, shell, shellArgs}) {
+  constructor({uid, rows, cols: columns, cwd, shell, shellArgs}) {
     const osLocale = require('os-locale');
     super();
     const baseEnv = Object.assign(
@@ -45,8 +97,6 @@ module.exports = class Session extends EventEmitter {
       delete baseEnv.GOOGLE_API_KEY;
     }
 
-    const decoder = new StringDecoder('utf8');
-
     const defaultShellArgs = ['--login'];
 
     try {
@@ -64,11 +114,16 @@ module.exports = class Session extends EventEmitter {
       }
     }
 
-    this.pty.on('data', data => {
+    this.batcher = new DataBatcher(uid);
+    this.pty.on('data', chunk => {
       if (this.ended) {
         return;
       }
-      this.emit('data', decoder.write(data));
+      this.batcher.write(chunk);
+    });
+
+    this.batcher.on('flush', data => {
+      this.emit('data', data);
     });
 
     this.pty.on('exit', () => {

app/ui/window.js

@@ -111,7 +111,7 @@ module.exports = class Window {
     function createInitialSession() {
       let {session, options} = createSession();
       const initialEvents = [];
-      const handleData = data => initialEvents.push(['session data', options.uid + data]);
+      const handleData = data => initialEvents.push(['session data', data]);
       const handleExit = () => initialEvents.push(['session exit']);
       session.on('data', handleData);
       session.on('exit', handleExit);
@@ -148,7 +148,7 @@ module.exports = class Window {
       }
 
       session.on('data', data => {
-        rpc.emit('session data', options.uid + data);
+        rpc.emit('session data', data);
       });
 
       session.on('exit', () => {