worker: enable stdio

Provide `stdin`, `stdout` and `stderr` options for the `Worker`
constructor, and make these available to the worker thread
under their usual names.

The default for `stdin` is an empty stream, the default for
`stdout` and `stderr` is redirecting to the parent thread’s
corresponding stdio streams.

PR-URL: #20876
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

Author: addaleax

doc/api/worker.md

@@ -240,7 +240,7 @@ Most Node.js APIs are available inside of it.
 Notable differences inside a Worker environment are:
 
 - The [`process.stdin`][], [`process.stdout`][] and [`process.stderr`][]
-  properties are set to `null`.
+  may be redirected by the parent thread.
 - The [`require('worker').isMainThread`][] property is set to `false`.
 - The [`require('worker').parentPort`][] message port is available,
 - [`process.exit()`][] does not stop the whole program, just the single thread,
@@ -313,6 +313,13 @@ if (isMainThread) {
     described in the [HTML structured clone algorithm][], and an error will be
     thrown if the object cannot be cloned (e.g. because it contains
     `function`s).
+  * stdin {boolean} If this is set to `true`, then `worker.stdin` will
+    provide a writable stream whose contents will appear as `process.stdin`
+    inside the Worker. By default, no data is provided.
+  * stdout {boolean} If this is set to `true`, then `worker.stdout` will
+    not automatically be piped through to `process.stdout` in the parent.
+  * stderr {boolean} If this is set to `true`, then `worker.stderr` will
+    not automatically be piped through to `process.stderr` in the parent.
 
 ### Event: 'error'
 <!-- YAML
@@ -377,6 +384,41 @@ Opposite of `unref()`, calling `ref()` on a previously `unref()`ed worker will
 behavior). If the worker is `ref()`ed, calling `ref()` again will have
 no effect.
 
+### worker.stderr
+<!-- YAML
+added: REPLACEME
+-->
+
+* {stream.Readable}
+
+This is a readable stream which contains data written to [`process.stderr`][]
+inside the worker thread. If `stderr: true` was not passed to the
+[`Worker`][] constructor, then data will be piped to the parent thread's
+[`process.stderr`][] stream.
+
+### worker.stdin
+<!-- YAML
+added: REPLACEME
+-->
+
+* {null|stream.Writable}
+
+If `stdin: true` was passed to the [`Worker`][] constructor, this is a
+writable stream. The data written to this stream will be made available in
+the worker thread as [`process.stdin`][].
+
+### worker.stdout
+<!-- YAML
+added: REPLACEME
+-->
+
+* {stream.Readable}
+
+This is a readable stream which contains data written to [`process.stdout`][]
+inside the worker thread. If `stdout: true` was not passed to the
+[`Worker`][] constructor, then data will be piped to the parent thread's
+[`process.stdout`][] stream.
+
 ### worker.terminate([callback])
 <!-- YAML
 added: REPLACEME

lib/internal/process/stdio.js

@@ -6,7 +6,10 @@ const {
   ERR_UNKNOWN_STDIN_TYPE,
   ERR_UNKNOWN_STREAM_TYPE
 } = require('internal/errors').codes;
-const { isMainThread } = require('internal/worker');
+const {
+  isMainThread,
+  workerStdio
+} = require('internal/worker');
 
 exports.setup = setupStdio;
 
@@ -17,8 +20,7 @@ function setupStdio() {
 
   function getStdout() {
     if (stdout) return stdout;
-    if (!isMainThread)
-      return new (require('stream').Writable)({ write(b, e, cb) { cb(); } });
+    if (!isMainThread) return workerStdio.stdout;
     stdout = createWritableStdioStream(1);
     stdout.destroySoon = stdout.destroy;
     stdout._destroy = function(er, cb) {
@@ -34,8 +36,7 @@ function setupStdio() {
 
   function getStderr() {
     if (stderr) return stderr;
-    if (!isMainThread)
-      return new (require('stream').Writable)({ write(b, e, cb) { cb(); } });
+    if (!isMainThread) return workerStdio.stderr;
     stderr = createWritableStdioStream(2);
     stderr.destroySoon = stderr.destroy;
     stderr._destroy = function(er, cb) {
@@ -51,8 +52,7 @@ function setupStdio() {
 
   function getStdin() {
     if (stdin) return stdin;
-    if (!isMainThread)
-      return new (require('stream').Readable)({ read() { this.push(null); } });
+    if (!isMainThread) return workerStdio.stdin;
 
     const tty_wrap = process.binding('tty_wrap');
     const fd = 0;

lib/internal/worker.js

@@ -5,6 +5,7 @@ const EventEmitter = require('events');
 const assert = require('assert');
 const path = require('path');
 const util = require('util');
+const { Readable, Writable } = require('stream');
 const {
   ERR_INVALID_ARG_TYPE,
   ERR_WORKER_NEED_ABSOLUTE_PATH,
@@ -29,13 +30,20 @@ const isMainThread = threadId === 0;
 
 const kOnMessageListener = Symbol('kOnMessageListener');
 const kHandle = Symbol('kHandle');
+const kName = Symbol('kName');
 const kPort = Symbol('kPort');
 const kPublicPort = Symbol('kPublicPort');
 const kDispose = Symbol('kDispose');
 const kOnExit = Symbol('kOnExit');
 const kOnMessage = Symbol('kOnMessage');
 const kOnCouldNotSerializeErr = Symbol('kOnCouldNotSerializeErr');
 const kOnErrorMessage = Symbol('kOnErrorMessage');
+const kParentSideStdio = Symbol('kParentSideStdio');
+const kWritableCallbacks = Symbol('kWritableCallbacks');
+const kStdioWantsMoreDataCallback = Symbol('kStdioWantsMoreDataCallback');
+const kStartedReading = Symbol('kStartedReading');
+const kWaitingStreams = Symbol('kWaitingStreams');
+const kIncrementsPortRef = Symbol('kIncrementsPortRef');
 
 const debug = util.debuglog('worker');
 
@@ -129,6 +137,72 @@ function setupPortReferencing(port, eventEmitter, eventName) {
 }
 
 
+class ReadableWorkerStdio extends Readable {
+  constructor(port, name) {
+    super();
+    this[kPort] = port;
+    this[kName] = name;
+    this[kIncrementsPortRef] = true;
+    this[kStartedReading] = false;
+    this.on('end', () => {
+      if (this[kIncrementsPortRef] && --this[kPort][kWaitingStreams] === 0)
+        this[kPort].unref();
+    });
+  }
+
+  _read() {
+    if (!this[kStartedReading] && this[kIncrementsPortRef]) {
+      this[kStartedReading] = true;
+      if (this[kPort][kWaitingStreams]++ === 0)
+        this[kPort].ref();
+    }
+
+    this[kPort].postMessage({
+      type: 'stdioWantsMoreData',
+      stream: this[kName]
+    });
+  }
+}
+
+class WritableWorkerStdio extends Writable {
+  constructor(port, name) {
+    super({ decodeStrings: false });
+    this[kPort] = port;
+    this[kName] = name;
+    this[kWritableCallbacks] = [];
+  }
+
+  _write(chunk, encoding, cb) {
+    this[kPort].postMessage({
+      type: 'stdioPayload',
+      stream: this[kName],
+      chunk,
+      encoding
+    });
+    this[kWritableCallbacks].push(cb);
+    if (this[kPort][kWaitingStreams]++ === 0)
+      this[kPort].ref();
+  }
+
+  _final(cb) {
+    this[kPort].postMessage({
+      type: 'stdioPayload',
+      stream: this[kName],
+      chunk: null
+    });
+    cb();
+  }
+
+  [kStdioWantsMoreDataCallback]() {
+    const cbs = this[kWritableCallbacks];
+    this[kWritableCallbacks] = [];
+    for (const cb of cbs)
+      cb();
+    if ((this[kPort][kWaitingStreams] -= cbs.length) === 0)
+      this[kPort].unref();
+  }
+}
+
 class Worker extends EventEmitter {
   constructor(filename, options = {}) {
     super();
@@ -154,8 +228,25 @@ class Worker extends EventEmitter {
     this[kPort].on('message', (data) => this[kOnMessage](data));
     this[kPort].start();
     this[kPort].unref();
+    this[kPort][kWaitingStreams] = 0;
     debug(`[${threadId}] created Worker with ID ${this.threadId}`);
 
+    let stdin = null;
+    if (options.stdin)
+      stdin = new WritableWorkerStdio(this[kPort], 'stdin');
+    const stdout = new ReadableWorkerStdio(this[kPort], 'stdout');
+    if (!options.stdout) {
+      stdout[kIncrementsPortRef] = false;
+      pipeWithoutWarning(stdout, process.stdout);
+    }
+    const stderr = new ReadableWorkerStdio(this[kPort], 'stderr');
+    if (!options.stderr) {
+      stderr[kIncrementsPortRef] = false;
+      pipeWithoutWarning(stderr, process.stderr);
+    }
+
+    this[kParentSideStdio] = { stdin, stdout, stderr };
+
     const { port1, port2 } = new MessageChannel();
     this[kPublicPort] = port1;
     this[kPublicPort].on('message', (message) => this.emit('message', message));
@@ -165,7 +256,8 @@ class Worker extends EventEmitter {
       filename,
       doEval: !!options.eval,
       workerData: options.workerData,
-      publicPort: port2
+      publicPort: port2,
+      hasStdin: !!options.stdin
     }, [port2]);
     // Actually start the new thread now that everything is in place.
     this[kHandle].startThread();
@@ -197,6 +289,16 @@ class Worker extends EventEmitter {
         return this[kOnCouldNotSerializeErr]();
       case 'errorMessage':
         return this[kOnErrorMessage](message.error);
+      case 'stdioPayload':
+      {
+        const { stream, chunk, encoding } = message;
+        return this[kParentSideStdio][stream].push(chunk, encoding);
+      }
+      case 'stdioWantsMoreData':
+      {
+        const { stream } = message;
+        return this[kParentSideStdio][stream][kStdioWantsMoreDataCallback]();
+      }
     }
 
     assert.fail(`Unknown worker message type ${message.type}`);
@@ -207,6 +309,18 @@ class Worker extends EventEmitter {
     this[kHandle] = null;
     this[kPort] = null;
     this[kPublicPort] = null;
+
+    const { stdout, stderr } = this[kParentSideStdio];
+    this[kParentSideStdio] = null;
+
+    if (!stdout._readableState.ended) {
+      debug(`[${threadId}] explicitly closes stdout for ${this.threadId}`);
+      stdout.push(null);
+    }
+    if (!stderr._readableState.ended) {
+      debug(`[${threadId}] explicitly closes stderr for ${this.threadId}`);
+      stderr.push(null);
+    }
   }
 
   postMessage(...args) {
@@ -243,6 +357,27 @@ class Worker extends EventEmitter {
 
     return this[kHandle].threadId;
   }
+
+  get stdin() {
+    return this[kParentSideStdio].stdin;
+  }
+
+  get stdout() {
+    return this[kParentSideStdio].stdout;
+  }
+
+  get stderr() {
+    return this[kParentSideStdio].stderr;
+  }
+}
+
+const workerStdio = {};
+if (!isMainThread) {
+  const port = getEnvMessagePort();
+  port[kWaitingStreams] = 0;
+  workerStdio.stdin = new ReadableWorkerStdio(port, 'stdin');
+  workerStdio.stdout = new WritableWorkerStdio(port, 'stdout');
+  workerStdio.stderr = new WritableWorkerStdio(port, 'stderr');
 }
 
 let originalFatalException;
@@ -256,10 +391,14 @@ function setupChild(evalScript) {
 
   port.on('message', (message) => {
     if (message.type === 'loadScript') {
-      const { filename, doEval, workerData, publicPort } = message;
+      const { filename, doEval, workerData, publicPort, hasStdin } = message;
       publicWorker.parentPort = publicPort;
       setupPortReferencing(publicPort, publicPort, 'message');
       publicWorker.workerData = workerData;
+
+      if (!hasStdin)
+        workerStdio.stdin.push(null);
+
       debug(`[${threadId}] starts worker script ${filename} ` +
             `(eval = ${eval}) at cwd = ${process.cwd()}`);
       port.unref();
@@ -271,6 +410,14 @@ function setupChild(evalScript) {
         require('module').runMain();
       }
       return;
+    } else if (message.type === 'stdioPayload') {
+      const { stream, chunk, encoding } = message;
+      workerStdio[stream].push(chunk, encoding);
+      return;
+    } else if (message.type === 'stdioWantsMoreData') {
+      const { stream } = message;
+      workerStdio[stream][kStdioWantsMoreDataCallback]();
+      return;
     }
 
     assert.fail(`Unknown worker message type ${message.type}`);
@@ -317,11 +464,24 @@ function deserializeError(error) {
                      error.byteLength).toString('utf8');
 }
 
+function pipeWithoutWarning(source, dest) {
+  const sourceMaxListeners = source._maxListeners;
+  const destMaxListeners = dest._maxListeners;
+  source.setMaxListeners(Infinity);
+  dest.setMaxListeners(Infinity);
+
+  source.pipe(dest);
+
+  source._maxListeners = sourceMaxListeners;
+  dest._maxListeners = destMaxListeners;
+}
+
 module.exports = {
   MessagePort,
   MessageChannel,
   threadId,
   Worker,
   setupChild,
-  isMainThread
+  isMainThread,
+  workerStdio
 };