TypeError: process.send is not a function

[thomasstjerne]

Node version v18.12.1 with ES modules.

import { pool } from "workerpool";
import { dirname } from 'path';
import { fileURLToPath } from 'url';
const __dirname = dirname(fileURLToPath(import.meta.url));
const poolOfWorkers = pool(__dirname + '/myWorker.js');

poolOfWorkers.exec(aFunctionDefinedInMyWorker, params)

TypeError: process.send is not a function
    at worker.send (/......../node_modules/workerpool/src/worker.js:63:15)

https://github.com/josdejong/workerpool/blob/68b98633ed1a93eda4347f6761ef675a0d3beaad/src/worker.js#L63

[josdejong]

How to reproduce this issue? Can you share a minimal example that demonstrates the issue?

[NickKelly1]

Had the same issue in NodeJS using worker threads.

Solution was to stop calling workerpool.worker(...) in the main thread. workerpool.worker tries to communicate with the main thread which breaks when executed from the main thread. It tries to use parentPort but that only exists on worker threads so the package falls back to process.send which doesn't exist either because the process wasn't spawned with an IPC channel, hence the error message.

For example:

package.json

{
  "type": "module",
  "dependencies": {
    "workerpool": "^6.4.0"
  }
}

main.js

// cjs
// const wt = require('worker_threads');
// const wp = require('workerpool');
// esm
import { fileURLToPath } from 'url';
import * as wt from 'worker_threads';
import wp from 'workerpool';

const ctx = wt.isMainThread ? '[main]' : '[worker]';
console.log(ctx);

// if (!wt.isMainThread) {
  wp.worker({
    work() { console.log(ctx, 'working'); }
  });
// }

if (wt.isMainThread) {
  // const thisFilename = __filename; // cjs
  const thisFilename = fileURLToPath(import.meta.url); // esm
  const pool = wp.pool(thisFilename, { workerType: 'thread', });
  pool
    .exec('work', null, { })
    .then(function() { console.log(ctx, 'done'); })
    .catch(function(err) { console.log(ctx, 'error', err); })
    .then(function() { pool.terminate(); })
}

execution

➜  example node main.js                  
[main]
.../example/node_modules/workerpool/src/worker.js:63
      process.send(message);
              ^

TypeError: process.send is not a function
    at worker.send (.../example/node_modules/workerpool/src/worker.js:63:15)
    at worker.register [as add] (.../example/node_modules/workerpool/src/worker.js:238:10)
    at Object.worker (.../example/node_modules/workerpool/src/index.js:22:10)
    at file:///.../example/main.js:13:6
    at ModuleJob.run (node:internal/modules/esm/module_job:192:25)

Node.js v20.2.0

Fixed by uncommenting the conditional // if (!wt.isMainThread) {

[josdejong]

Thanks for sharing Nick!

The workerpool.worker method is indeed only usable on the worker side, not in the main thread.

I'll close this issue now.

[luluhoc]

Just for anybody having this problem, for me it was that I accidentally exported a function and imported it in main thread 🔢