It locks promise's `resolv()` inside mocha tests.

[aurium]

Hi folks. That is a weird bug or a big mistake. I need your help to solve anyway. I'm trying to make synaptic.js to work in parallel in node.js, and @Jabher point me this project to make the job without local WebWorker re-implementation. The problem is: with webworker-threads the mocha test freezes until timeout.

I did simplify the test to point you where it happens without synaptic.js code:

describe('Weird Things', function () {
  this.timeout(5000);

  it('Listen wwthreads message', function (done) {
    var Worker = require('webworker-threads').Worker;
    w = new Worker(new Function('postMessage("t1: OK")'));
    w.onmessage = function(msg){
      console.log('t1: Mesage:',msg);
      done();
      console.log('t1: done() was called.');
    };
  });

  it("Promise resolved by timeout", function (done) {
    new Promise(function(resolve, reject) {
      try {
        setTimeout(function(){
          console.log('t2: Timeout.');
          resolve();
          console.log('t2: resolve() was called.');
        }, 100);
      } catch(e) {
        reject(e)
      }
    }).then(function(){ done(); console.log('t2: then() was called') });
  });

  it("Promise resolved by listen wwthreads message", function (done) {
    new Promise(function(resolve, reject) {
      try {
        var Worker = require('webworker-threads').Worker;
        w = new Worker(new Function('postMessage("t3: OK")'));
        w.onmessage = function(msg){
          console.log('t3: Mesage:',msg);
          resolve();
          console.log('t3: resolve() was called.');
        };
      } catch(e) {
        reject(e)
      }
    }).then(function(){ done(); console.log('t3: then() was called') });
  });

});

And it outputs:

  Weird Things
t1: Mesage: { data: 't1: OK' }
    ✓ Listen wwthreads message
t1: done() was called.
t2: Timeout.
t2: resolve() was called.
    ✓ Promise resolved by timeout (105ms)
t2: then() was called
t3: Mesage: { data: 't3: OK' }
t3: resolve() was called.
    1) Promise resolved by listen wwthreads message
t3: then() was called

  2 passing (5s)
  1 failing

  1) Weird Things Promise resolved by listen wwthreads message:
     Error: timeout of 5000ms exceeded. Ensure the done() callback is being called in this test.

As you can see, only when we mix Promise with webworker-threads the problem appear, and the then() was called, only after the timeout, doesn't matter how long it is.

You can see why it need this test to work at Trainer::trainAsync(). I believe that can be a problem to many other possible webworker-threads uses. That is not a problem if i implement the same feature with child_process module mimicking WebWorkers.

Thanks.

[EduardoRFS]

When event queue is empty, node eventloop close, webworker need to keep events in queue, like cluster module

[brodycj]

I think this needs documentation.

[aurium]

I believe it is not a open question, it is a bug. @EduardoRFS makes a god point on event queue.

[tswaters]

See the following issue: https://github.com/audreyt/node-webworker-threads/issues/93 -- basically, wrap with setImmediate

I had a similar issue first time using this module. Had something like this:

return new Promise((resolve, reject) => {
  t.eval('fibo(10)', (err, result) => {
    if (err) { return reject(err) }
    resolve(result)
  })
})

And it would hang for sometimes upwards of 30 seconds before responding. I thought it was theads being weird, building on windows, something.... changed it to wrap the resolution/rejection in setImmediate and it works much better

return new Promise((resolve, reject) => {
  t.eval('fibo(10)', (err, result) => {
    setImmediate(() => {
      if (err) { return reject(err) }
      resolve(result)
    })
  })
})

[joshjung]

Still having this issue over a year later :(

[audreyt]

Hi! This module's functionality is now part of Node core https://nodejs.org/api/worker_threads.html

If you would like, I wonder if you (or someone interested) can help create a compatibility API on top of the core Node API and thus make this extension a polyfill only for earlier Node versions?