Process and Workers

const port = Number(process.env.PORT ?? 3000);
Number.isFinite(port)  // true
const args = process.argv.slice(2);
Array.isArray(args)    // true

import { spawn } from "node:child_process";
const child = spawn(process.execPath, ["-e", "console.log(1)"], {
  encoding: "utf8" as any,
});
let out = "";
child.stdout?.on("data", (c) => { out += c; });
const code = await new Promise<number | null>((res) => child.on("close", res));
code  // 0
out.trim()  // "1"

import { execFile } from "node:child_process";
import { promisify } from "node:util";
const execFileAsync = promisify(execFile);
const { stdout } = await execFileAsync(process.execPath, ["-e", "console.log(1)"]);
stdout.trim()  // "1"

import { Worker } from "node:worker_threads";
// const worker = new Worker(new URL("./cpu-job.js", import.meta.url));
// worker.postMessage({ n: 40 });
typeof Worker  // "function"

import { parentPort, isMainThread } from "node:worker_threads";
isMainThread  // true in this file
// in worker: parentPort?.postMessage({ ok: true });

import { workerData } from "node:worker_threads";
// new Worker(file, { workerData: { jobId: "x" } });
// inside worker: workerData.jobId === "x"
typeof workerData  // "object" | may be empty on main

import path from "node:path";
path.isAbsolute(process.cwd())  // true
// process.chdir("/tmp");

process.exitCode = 0;
process.exitCode  // 0
// on failure: process.exitCode = 1;

import { Readable } from "node:stream";
const lines: string[] = [];
for await (const line of Readable.from(["a\n", "b\n"])) {
  lines.push(String(line).trim());
}
lines  // ["a", "b"]

const sab = new SharedArrayBuffer(4);
const view = new Int32Array(sab);
Atomics.store(view, 0, 7);
Atomics.load(view, 0)  // 7

import { fork } from "node:child_process";
typeof fork  // "function"
// const child = fork("./worker-entry.js");
// child.send({ type: "start" });

const m = process.memoryUsage();
m.rss > 0        // true
m.heapUsed > 0   // true

// UV_THREADPOOL_SIZE=16 node app.js
// default pool size is 4
process.env.UV_THREADPOOL_SIZE ?? "4"  // "4" unless set

// process.on("unhandledRejection", (reason) => {
//   console.error(reason);
//   process.exit(1);
// });
typeof process.on  // "function"

import { MessageChannel } from "node:worker_threads";
const { port1, port2 } = new MessageChannel();
const seen: unknown[] = [];
port1.on("message", (m) => seen.push(m));
port2.postMessage({ hi: true });
await new Promise((r) => setImmediate(r));
seen
// [{ hi: true }]