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BaseWorkerPool.ts
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/**
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
import mergeStream = require('merge-stream');
import {
CHILD_MESSAGE_CALL_SETUP,
CHILD_MESSAGE_END,
type PoolExitResult,
type WorkerInterface,
type WorkerOptions,
type WorkerPoolOptions,
WorkerStates,
} from '../types';
// How long to wait for the child process to terminate
// after CHILD_MESSAGE_END before sending force exiting.
const FORCE_EXIT_DELAY = 500;
/* istanbul ignore next */
// eslint-disable-next-line @typescript-eslint/no-empty-function
const emptyMethod = () => {};
export default class BaseWorkerPool {
private readonly _stderr: NodeJS.ReadableStream;
private readonly _stdout: NodeJS.ReadableStream;
protected readonly _options: WorkerPoolOptions;
private readonly _workers: Array<WorkerInterface>;
private readonly _workerPath: string;
constructor(workerPath: string, options: WorkerPoolOptions) {
this._options = options;
this._workerPath = workerPath;
this._workers = Array.from({length: options.numWorkers});
const stdout = mergeStream();
const stderr = mergeStream();
const {forkOptions, maxRetries, resourceLimits, setupArgs} = options;
for (let i = 0; i < options.numWorkers; i++) {
const workerOptions: WorkerOptions = {
forkOptions,
idleMemoryLimit: this._options.idleMemoryLimit,
maxRetries,
resourceLimits,
setupArgs,
workerId: i,
workerPath,
};
const worker = this.createWorker(workerOptions);
const workerStdout = worker.getStdout();
const workerStderr = worker.getStderr();
if (workerStdout) {
stdout.add(workerStdout);
}
if (workerStderr) {
stderr.add(workerStderr);
}
this._workers[i] = worker;
}
this._stdout = stdout;
this._stderr = stderr;
}
getStderr(): NodeJS.ReadableStream {
return this._stderr;
}
getStdout(): NodeJS.ReadableStream {
return this._stdout;
}
getWorkers(): Array<WorkerInterface> {
return this._workers;
}
getWorkerById(workerId: number): WorkerInterface {
return this._workers[workerId];
}
restartWorkerIfShutDown(workerId: number): void {
if (this._workers[workerId].state === WorkerStates.SHUT_DOWN) {
const {forkOptions, maxRetries, resourceLimits, setupArgs} =
this._options;
const workerOptions: WorkerOptions = {
forkOptions,
idleMemoryLimit: this._options.idleMemoryLimit,
maxRetries,
resourceLimits,
setupArgs,
workerId,
workerPath: this._workerPath,
};
const worker = this.createWorker(workerOptions);
this._workers[workerId] = worker;
}
}
createWorker(_workerOptions: WorkerOptions): WorkerInterface {
throw new Error('Missing method createWorker in WorkerPool');
}
async start(): Promise<void> {
await Promise.all(
this._workers.map(async worker => {
await worker.waitForWorkerReady();
await new Promise<void>((resolve, reject) => {
worker.send(
[CHILD_MESSAGE_CALL_SETUP],
emptyMethod,
error => {
if (error) {
reject(error);
} else {
resolve();
}
},
emptyMethod,
);
});
}),
);
}
async end(): Promise<PoolExitResult> {
// We do not cache the request object here. If so, it would only be only
// processed by one of the workers, and we want them all to close.
const workerExitPromises = this._workers.map(async worker => {
worker.send(
[CHILD_MESSAGE_END, false],
emptyMethod,
emptyMethod,
emptyMethod,
);
// Schedule a force exit in case worker fails to exit gracefully so
// await worker.waitForExit() never takes longer than FORCE_EXIT_DELAY
let forceExited = false;
const forceExitTimeout = setTimeout(() => {
worker.forceExit();
forceExited = true;
}, FORCE_EXIT_DELAY);
await worker.waitForExit();
// Worker ideally exited gracefully, don't send force exit then
clearTimeout(forceExitTimeout);
return forceExited;
});
const workerExits = await Promise.all(workerExitPromises);
return workerExits.reduce<PoolExitResult>(
(result, forceExited) => ({
forceExited: result.forceExited || forceExited,
}),
{forceExited: false},
);
}
}