PM2: process.on('message') prevent process to be stopped.

What's going wrong?

process.on('message') prevent process to be stopped even when no more operations are pending.

How could we reproduce this issue?

// index.js
console.log('Log 1');
process.on('message', () => {});
console.log('Log 2');

PM2 Start

pm2 start index.js --no-autorestart

Output

[PM2] Starting C:\Users\<USERNAME>\Desktop\exp-pm2\index.js in fork_mode (1 instance)
[PM2] Done.
┌────┬────────────────────┬──────────┬──────┬───────────┬──────────┬──────────┐
│ id │ name               │ mode     │ ↺    │ status    │ cpu      │ memory   │                         
├────┼────────────────────┼──────────┼──────┼───────────┼──────────┼──────────┤
│ 0  │ index              │ fork     │ 0    │ online    │ 10.8%    │ 25.6mb   │                         
└────┴────────────────────┴──────────┴──────┴───────────┴──────────┴──────────┘

PM2 Logs

pm2 logs

Output

[TAILING] Tailing last 15 lines for [all] processes (change the value with --lines option)
PM2      | App [index:0] starting in -fork mode-
PM2      | App [index:0] online
0|index  | Log 1
0|index  | Log 2

No Exit in HERE.

PM2 List

pm2 list

Output

┌────┬────────────────────┬──────────┬──────┬───────────┬──────────┬──────────┐
│ id │ name               │ mode     │ ↺    │ status    │ cpu      │ memory   │
├────┼────────────────────┼──────────┼──────┼───────────┼──────────┼──────────┤
│ 0  │ index              │ fork     │ 0    │ online    │ 0%       │ 22.7mb   │
└────┴────────────────────┴──────────┴──────┴───────────┴──────────┴──────────┘

Still Online.

Supporting information

$ pm2 report

Output

--- PM2 report ----------------------------------------------------------------
Date                 : Tue Sep 08 2020 09:20:51 GMT+0200 (Eastern European Standard Time)
===============================================================================
--- Daemon -------------------------------------------------
pm2d version         : 4.4.1
node version         : 12.14.0
node path            : not found
argv                 : C:\Program Files\nodejs\node.exe,C:\Users\<USERNAME>\AppData\Roaming\npm\node_modules\pm2\lib\Daemon.js
argv0                : node
user                 : undefined
uid                  : N/A
gid                  : N/A
uptime               : 1403min
===============================================================================
--- CLI ----------------------------------------------------
local pm2            : 4.4.1
node version         : 12.14.0
node path            : not found
argv                 : C:\Program Files\nodejs\node.exe,C:\Users\<USERNAME>\AppData\Roaming\npm\node_modules\pm2\bin\pm2,report
argv0                : C:\Program Files\nodejs\node.exe
user                 : <USERNAME>
===============================================================================
--- System info --------------------------------------------
arch                 : x64
platform             : win32
type                 : Windows_NT
cpus                 : Intel(R) Xeon(R) CPU           X5680  @ 3.33GHz
cpus nb              : 6
freemem              : 8952524800
totalmem             : 17177333760
home                 : C:\Users\<USERNAME>
===============================================================================
--- PM2 list -----------------------------------------------
┌────┬────────────────────┬──────────┬──────┬───────────┬──────────┬──────────┐
│ id │ name               │ mode     │ ↺    │ status    │ cpu      │ memory   │
├────┼────────────────────┼──────────┼──────┼───────────┼──────────┼──────────┤
│ 0  │ index              │ fork     │ 0    │ online    │ 0%       │ 22.2mb   │
└────┴────────────────────┴──────────┴──────┴───────────┴──────────┴──────────┘
===============================================================================

Of course we can us removeListener to stop listening to message event, but I guess it's not a good solution.

Start with the provided index.js reproduction and run it through pm2 start index.js --no-autorestart, then inspect the PM2 process-management entry points involved in stopping forked applications. Done means a process that only registers process.on('message') exits naturally and PM2 no longer reports it as online.