Add worker-based sharding to the ShardingManager (#2908)

* Add worker-based sharding mode to ShardingManager

* Fix ClientShardUtil mode

* Fix worker not being cleared on shard death

* Update docs and typings

* Clean up Client sharding logic a bit

* Add info about requirements for worker mode

src/client/Client.js

@@ -31,12 +31,30 @@ class Client extends BaseClient {
   constructor(options = {}) {
     super(Object.assign({ _tokenType: 'Bot' }, options));
 
-    // Obtain shard details from environment
-    if (!browser && !this.options.shardId && 'SHARD_ID' in process.env) {
-      this.options.shardId = Number(process.env.SHARD_ID);
-    }
-    if (!browser && !this.options.shardCount && 'SHARD_COUNT' in process.env) {
-      this.options.shardCount = Number(process.env.SHARD_COUNT);
+    // Figure out the shard details
+    if (!browser && process.env.SHARDING_MANAGER) {
+      // Try loading workerData if it's present
+      let workerData;
+      try {
+        workerData = require('worker_threads').workerData;
+      } catch (err) {
+        // Do nothing
+      }
+
+      if (!this.options.shardId) {
+        if (workerData && 'SHARD_ID' in workerData) {
+          this.options.shardId = workerData.SHARD_ID;
+        } else if ('SHARD_ID' in process.env) {
+          this.options.shardId = Number(process.env.SHARD_ID);
+        }
+      }
+      if (!this.options.shardCount) {
+        if (workerData && 'SHARD_COUNT' in workerData) {
+          this.options.shardCount = workerData.SHARD_COUNT;
+        } else if ('SHARD_COUNT' in process.env) {
+          this.options.shardCount = Number(process.env.SHARD_COUNT);
+        }
+      }
     }
 
     this._validateOptions();
@@ -73,7 +91,9 @@ class Client extends BaseClient {
      * Shard helpers for the client (only if the process was spawned from a {@link ShardingManager})
      * @type {?ShardClientUtil}
      */
-    this.shard = !browser && process.env.SHARDING_MANAGER ? ShardClientUtil.singleton(this) : null;
+    this.shard = !browser && process.env.SHARDING_MANAGER ?
+      ShardClientUtil.singleton(this, process.env.SHARDING_MANAGER_MODE) :
+      null;
 
     /**
      * All of the {@link User} objects that have been cached at any point, mapped by their IDs

src/sharding/Shard.js

@@ -1,13 +1,14 @@
-const childProcess = require('child_process');
 const EventEmitter = require('events');
 const path = require('path');
 const Util = require('../util/Util');
 const { Error } = require('../errors');
+let childProcess = null;
+let Worker = null;
 
 /**
  * A self-contained shard created by the {@link ShardingManager}. Each one has a {@link ChildProcess} that contains
- * an instance of the bot and its {@link Client}. When its child process exits for any reason, the shard will spawn a
- * new one to replace it as necessary.
+ * an instance of the bot and its {@link Client}. When its child process/worker exits for any reason, the shard will
+ * spawn a new one to replace it as necessary.
  * @extends EventEmitter
  */
 class Shard extends EventEmitter {
@@ -18,6 +19,9 @@ class Shard extends EventEmitter {
   constructor(manager, id) {
     super();
 
+    if (manager.mode === 'process') childProcess = require('child_process');
+    else if (manager.mode === 'worker') Worker = require('worker_threads').Worker;
+
     /**
      * Manager that created the shard
      * @type {ShardingManager}
@@ -31,26 +35,24 @@ class Shard extends EventEmitter {
     this.id = id;
 
     /**
-     * Arguments for the shard's process
+     * Arguments for the shard's process (only when {@link ShardingManager#mode} is `process`)
      * @type {string[]}
      */
     this.args = manager.shardArgs || [];
 
     /**
-     * Arguments for the shard's process executable
+     * Arguments for the shard's process executable (only when {@link ShardingManager#mode} is `process`)
      * @type {?string[]}
      */
     this.execArgv = manager.execArgv;
 
     /**
-     * Environment variables for the shard's process
+     * Environment variables for the shard's process, or workerData for the shard's worker
      * @type {Object}
      */
     this.env = Object.assign({}, process.env, {
-      SHARDING_MANAGER: true,
       SHARD_ID: this.id,
       SHARD_COUNT: this.manager.totalShards,
-      DISCORD_TOKEN: this.manager.token,
     });
 
     /**
@@ -60,11 +62,17 @@ class Shard extends EventEmitter {
     this.ready = false;
 
     /**
-     * Process of the shard
+     * Process of the shard (if {@link ShardingManager#mode} is `process`)
      * @type {?ChildProcess}
      */
     this.process = null;
 
+    /**
+     * Worker of the shard (if {@link ShardingManager#mode} is `worker`)
+     * @type {?Worker}
+     */
+    this.worker = null;
+
     /**
      * Ongoing promises for calls to {@link Shard#eval}, mapped by the `script` they were called with
      * @type {Map<string, Promise>}
@@ -88,49 +96,62 @@ class Shard extends EventEmitter {
   }
 
   /**
-   * Forks a child process for the shard.
+   * Forks a child process or creates a worker thread for the shard.
    * <warn>You should not need to call this manually.</warn>
    * @param {boolean} [waitForReady=true] Whether to wait until the {@link Client} has become ready before resolving
    * @returns {Promise<ChildProcess>}
    */
   async spawn(waitForReady = true) {
     if (this.process) throw new Error('SHARDING_PROCESS_EXISTS', this.id);
-
-    this.process = childProcess.fork(path.resolve(this.manager.file), this.args, {
-      env: this.env, execArgv: this.execArgv,
-    })
-      .on('message', this._handleMessage.bind(this))
-      .on('exit', this._exitListener);
+    if (this.worker) throw new Error('SHARDING_WORKER_EXISTS', this.id);
+
+    if (this.manager.mode === 'process') {
+      this.process = childProcess.fork(path.resolve(this.manager.file), this.args, {
+        env: this.env, execArgv: this.execArgv,
+      })
+        .on('message', this._handleMessage.bind(this))
+        .on('exit', this._exitListener);
+    } else if (this.manager.mode === 'worker') {
+      this.worker = new Worker(path.resolve(this.manager.file), { workerData: this.env })
+        .on('message', this._handleMessage.bind(this))
+        .on('exit', this._exitListener);
+    }
 
     /**
-     * Emitted upon the creation of the shard's child process.
+     * Emitted upon the creation of the shard's child process/worker.
      * @event Shard#spawn
-     * @param {ChildProcess} process Child process that was created
+     * @param {ChildProcess|Worker} process Child process/worker that was created
      */
-    this.emit('spawn', this.process);
+    this.emit('spawn', this.process || this.worker);
 
-    if (!waitForReady) return this.process;
+    if (!waitForReady) return this.process || this.worker;
     await new Promise((resolve, reject) => {
       this.once('ready', resolve);
       this.once('disconnect', () => reject(new Error('SHARDING_READY_DISCONNECTED', this.id)));
       this.once('death', () => reject(new Error('SHARDING_READY_DIED', this.id)));
       setTimeout(() => reject(new Error('SHARDING_READY_TIMEOUT', this.id)), 30000);
     });
-    return this.process;
+    return this.process || this.worker;
   }
 
   /**
-   * Immediately kills the shard's process and does not restart it.
+   * Immediately kills the shard's process/worker and does not restart it.
    */
   kill() {
-    this.process.removeListener('exit', this._exitListener);
-    this.process.kill();
+    if (this.process) {
+      this.process.removeListener('exit', this._exitListener);
+      this.process.kill();
+    } else {
+      this.worker.removeListener('exit', this._exitListener);
+      this.worker.terminate();
+    }
+
     this._handleExit(false);
   }
 
   /**
-   * Kills and restarts the shard's process.
-   * @param {number} [delay=500] How long to wait between killing the process and restarting it (in milliseconds)
+   * Kills and restarts the shard's process/worker.
+   * @param {number} [delay=500] How long to wait between killing the process/worker and restarting it (in milliseconds)
    * @param {boolean} [waitForReady=true] Whether to wait until the {@link Client} has become ready before resolving
    * @returns {Promise<ChildProcess>}
    */
@@ -141,15 +162,20 @@ class Shard extends EventEmitter {
   }
 
   /**
-   * Sends a message to the shard's process.
+   * Sends a message to the shard's process/worker.
    * @param {*} message Message to send to the shard
    * @returns {Promise<Shard>}
    */
   send(message) {
     return new Promise((resolve, reject) => {
-      this.process.send(message, err => {
-        if (err) reject(err); else resolve(this);
-      });
+      if (this.process) {
+        this.process.send(message, err => {
+          if (err) reject(err); else resolve(this);
+        });
+      } else {
+        this.worker.postMessage(message);
+        resolve(this);
+      }
     });
   }
 
@@ -166,16 +192,18 @@ class Shard extends EventEmitter {
     if (this._fetches.has(prop)) return this._fetches.get(prop);
 
     const promise = new Promise((resolve, reject) => {
+      const child = this.process || this.worker;
+
       const listener = message => {
         if (!message || message._fetchProp !== prop) return;
-        this.process.removeListener('message', listener);
+        child.removeListener('message', listener);
         this._fetches.delete(prop);
         resolve(message._result);
       };
-      this.process.on('message', listener);
+      child.on('message', listener);
 
       this.send({ _fetchProp: prop }).catch(err => {
-        this.process.removeListener('message', listener);
+        child.removeListener('message', listener);
         this._fetches.delete(prop);
         reject(err);
       });
@@ -194,17 +222,19 @@ class Shard extends EventEmitter {
     if (this._evals.has(script)) return this._evals.get(script);
 
     const promise = new Promise((resolve, reject) => {
+      const child = this.process || this.worker;
+
       const listener = message => {
         if (!message || message._eval !== script) return;
-        this.process.removeListener('message', listener);
+        child.removeListener('message', listener);
         this._evals.delete(script);
         if (!message._error) resolve(message._result); else reject(Util.makeError(message._error));
       };
-      this.process.on('message', listener);
+      child.on('message', listener);
 
       const _eval = typeof script === 'function' ? `(${script})(this)` : script;
       this.send({ _eval }).catch(err => {
-        this.process.removeListener('message', listener);
+        child.removeListener('message', listener);
         this._evals.delete(script);
         reject(err);
       });
@@ -215,7 +245,7 @@ class Shard extends EventEmitter {
   }
 
   /**
-   * Handles an IPC message.
+   * Handles a message received from the child process/worker.
    * @param {*} message Message received
    * @private
    */
@@ -283,28 +313,29 @@ class Shard extends EventEmitter {
     }
 
     /**
-     * Emitted upon recieving a message from the child process.
+     * Emitted upon recieving a message from the child process/worker.
      * @event Shard#message
      * @param {*} message Message that was received
      */
     this.emit('message', message);
   }
 
   /**
-   * Handles the shard's process exiting.
+   * Handles the shard's process/worker exiting.
    * @param {boolean} [respawn=this.manager.respawn] Whether to spawn the shard again
    * @private
    */
   _handleExit(respawn = this.manager.respawn) {
     /**
-     * Emitted upon the shard's child process exiting.
+     * Emitted upon the shard's child process/worker exiting.
      * @event Shard#death
-     * @param {ChildProcess} process Child process that exited
+     * @param {ChildProcess|Worker} process Child process/worker that exited
      */
-    this.emit('death', this.process);
+    this.emit('death', this.process || this.worker);
 
     this.ready = false;
     this.process = null;
+    this.worker = null;
     this._evals.clear();
     this._fetches.clear();