cluster: worker.disconnect() goes into forever loop though worker.isConnected() === true

[viliusl]

System info:

$ node -v
v4.4.3

$ uname -a
Darwin localhost 15.2.0 Darwin Kernel Version 15.2.0: Fri Nov 13 19:56:56 PST 2015; root:xnu-3248.20.55~2/RELEASE_X86_64 x86_64

verified for node@5 and node@6.

code:

'use strict';
const http = require('http'),
  cluster = require('cluster');

if (cluster.isMaster) {
  http.createServer().listen(3000);
  cluster.fork();
} else {
  process.on('uncaughtException', e => {
    console.log('uncaught', e);
    if (cluster.worker.isConnected() && !cluster.worker.isDead()) {
      cluster.worker.disconnect();
    }
  });
  http.createServer().listen(3000);
}

output:

$ node test
uncaught { Error: bind EADDRINUSE null:3000
    at Object.exports._errnoException (util.js:896:11)
    at exports._exceptionWithHostPort (util.js:919:20)
    at cb (net.js:1311:16)
    at rr (cluster.js:620:14)
    at Worker.<anonymous> (cluster.js:590:9)
    at process.<anonymous> (cluster.js:750:8)
    at emitTwo (events.js:111:20)
    at process.emit (events.js:191:7)
    at handleMessage (internal/child_process.js:718:10)
    at Pipe.channel.onread (internal/child_process.js:444:11)
  code: 'EADDRINUSE',
  errno: 'EADDRINUSE',
  syscall: 'bind',
  address: null,
  port: 3000 }
uncaught TypeError: Cannot read property 'apply' of undefined
    at process.<anonymous> (cluster.js:750:7)
    at emitTwo (events.js:111:20)
    at process.emit (events.js:191:7)
    at handleMessage (internal/child_process.js:718:10)
    at Pipe.channel.onread (internal/child_process.js:444:11)
uncaught TypeError: Cannot read property 'apply' of undefined
    at process.<anonymous> (cluster.js:750:7)
    at emitTwo (events.js:111:20)
    at process.emit (events.js:191:7)
    at handleMessage (internal/child_process.js:718:10)
    at Pipe.channel.onread (internal/child_process.js:444:11)

and it keeps going forever.

My expectations in this case:

• given worker says it's connected, worker.disconnect() should be safe.

Or maybe I'm just doing smth wrong here.

[sam-github]

You are doing something wrong, do not make async calls in an uncaughtException handler.

You don't need to disconnect, rethrow the exception (or don't catch it at all), and let the worker exit. The disconnect will happen automatically by the system.

[viliusl]

@sam-github thanks for clarification. Still it's quite strange and non-uniform behaviour.

Say code:

'use strict';
const http = require('http'),
  cluster = require('cluster');

if (cluster.isMaster) {
  cluster.on('disconnect', worker => {
    console.log('worker disconnected');
    worker.kill();
  });
  cluster.on('exit', worker => {
    console.log('worker exited');
    worker.kill();
  });

  const worker = cluster.fork();
} else {
  process.on('uncaughtException', e => {
    console.log('uncaught', e);
    if (cluster.worker.isConnected() && !cluster.worker.isDead()) {
      cluster.worker.disconnect();
    }
  });
  http.createServer().listen(3000, () => {throw new Error('qwe')});
}

or code:

'use strict';
const http = require('http'),
  cluster = require('cluster');

if (cluster.isMaster) {
  cluster.on('disconnect', worker => {
    console.log('worker disconnected');
    worker.kill();
  });
  cluster.on('exit', worker => {
    console.log('worker exited');
    worker.kill();
  });

  const worker = cluster.fork();
} else {
  process.on('uncaughtException', e => {
    console.log('uncaught', e);
    if (cluster.worker.isConnected() && !cluster.worker.isDead()) {
      cluster.worker.disconnect();
    }
  });
  process.nextTick(() => {throw new Error('qwe')});
}

yields output:

uncaught [Error: qwe]
worker disconnected
worker exited

Seems like same case (uncaught exception), but behaviour is different. I'm not sure if EADDRINUSE is somehow special error with specific handling, but from my (user) perspective both are uncaughtException's.

If you see this behaviour as correct and considering I'm doing a no-no thing (async in uncaughtException handler) you can close this issue.

Cheers,
V

[sam-github]

Sorry, should be more clear. I do think this is a bug, we should fix it (if we can, I assume we can).

However, you should also not be doing the thing you are doing, even if we did fix it.

[viliusl]

Thanks alot!