forked from sheetjs/docs.sheetjs.com
89 lines
2.6 KiB
JavaScript
89 lines
2.6 KiB
JavaScript
// This example from https://nodejs.org/dist/latest/docs/api/worker_threads.html
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// Documentation code redistributed under the MIT license.
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// Copyright Node.js contributors
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import { AsyncResource } from 'node:async_hooks';
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import { EventEmitter } from 'node:events';
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import { Worker } from 'node:worker_threads';
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const kTaskInfo = Symbol('kTaskInfo');
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const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
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class WorkerPoolTaskInfo extends AsyncResource {
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constructor(callback) {
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super('WorkerPoolTaskInfo');
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this.callback = callback;
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}
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done(err, result) {
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this.runInAsyncScope(this.callback, null, err, result);
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this.emitDestroy(); // `TaskInfo`s are used only once.
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}
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}
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export default class WorkerPool extends EventEmitter {
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constructor(numThreads) {
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super();
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this.numThreads = numThreads;
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this.workers = [];
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this.freeWorkers = [];
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this.tasks = [];
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for (let i = 0; i < numThreads; i++)
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this.addNewWorker();
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// Any time the kWorkerFreedEvent is emitted, dispatch
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// the next task pending in the queue, if any.
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this.on(kWorkerFreedEvent, () => {
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if (this.tasks.length > 0) {
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const { task, callback } = this.tasks.shift();
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this.runTask(task, callback);
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}
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});
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}
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addNewWorker() {
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const worker = new Worker(new URL('worker.js', import.meta.url));
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worker.on('message', (result) => {
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// In case of success: Call the callback that was passed to `runTask`,
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// remove the `TaskInfo` associated with the Worker, and mark it as free
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// again.
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worker[kTaskInfo].done(null, result);
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worker[kTaskInfo] = null;
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this.freeWorkers.push(worker);
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this.emit(kWorkerFreedEvent);
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});
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worker.on('error', (err) => {
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// In case of an uncaught exception: Call the callback that was passed to
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// `runTask` with the error.
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if (worker[kTaskInfo])
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worker[kTaskInfo].done(err, null);
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else
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this.emit('error', err);
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// Remove the worker from the list and start a new Worker to replace the
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// current one.
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this.workers.splice(this.workers.indexOf(worker), 1);
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this.addNewWorker();
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});
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this.workers.push(worker);
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this.freeWorkers.push(worker);
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this.emit(kWorkerFreedEvent);
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}
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runTask(task, callback) {
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if (this.freeWorkers.length === 0) {
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// No free threads, wait until a worker thread becomes free.
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this.tasks.push({ task, callback });
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return;
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}
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const worker = this.freeWorkers.pop();
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worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
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worker.postMessage(task);
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}
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close() {
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for (const worker of this.workers) worker.terminate();
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}
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}
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