Missing queued cbs when call pool.end()

[iammapping]

The callbacks in pool._connectionQueue would never been executed, when calling pool.end(). I think it is necessary to append the under segment to function Pool.prototype.end

while (this._connectionQueue.length > 0) {
  // tell callback in queue that the pool is ended
  this._connectionQueue.shift()(new Error('Pool is ended'), null);
}

[dougwilson]

I altered your issue title because it's not a memory leak; not calling callbacks does not leak memory, that's not how JavaScript works. But I do see what you mean about the connection queue. I've scheduled the fix for 2.2.

[iammapping]

@dougwilson Sorry. I didn't explain clearly. This may cause user's program leaking memory, such as:

var mysql = require('mysql');
var pool  = null;
var count = 1;

var createPool = function() {
  // recreate pool while it is closed
  if (!pool) {
    pool = mysql.createPool({
      host: '127.0.0.1',
      user: 'root',
      password: '',
      connectionLimit: 1
    })
  }
};


setInterval(function(req, res) {
  // allocate a large array
  var size = 10 * 1024 * 1024;
  var arr = new Array(size);
  for (var i = 0; i < size; i++) {
    arr[i] = 0;
  }

  createPool();

  // make sure the other callbacks pushed into connection queue
  pool.query('SELECT SLEEP(1000)', function(err) {
    // free the large array in callback
    arr = null;
    if (err) {
      // console.log(err)
      pool = null;
    }
  });

  // call pool.end every 5 times
  if (count % 5 === 0) {
    pool && pool.end(function(err) {});
  }

  // print memory usage
  var mem = process.memoryUsage();
  var format = function(bytes) {
    return (bytes / 1024 / 1024).toFixed(2) + 'MB';
  };
  console.log('Process ' + count + ': heapTotal ' + format(mem.heapTotal) + ' heapUsed ' + format(mem.heapUsed) + ' rss ' + format(mem.rss));
  console.log('-----------------------------------------------------');

  count++
}, 10);

[dougwilson]

This is fixed now.

[iammapping]

@dougwilson Hi, I'm looking at your last commit, but the bug I posted still exists. The callbacks in pool's connection queue would never been executed. I wrote a demo to reappear, you can run the under code:

var mysql = require('mysql');
var pool  = null;
var count = 1;

pool = mysql.createPool({
  host: '127.0.0.1',
  user: 'root',
  password: '',
  connectionLimit: 1
});

var interval = setInterval(function(req, res) {
  (function(cbIndex) {
    // make sure the other callbacks pushed into connection queue
    pool.query('SELECT SLEEP(10)', function(err) {
      if (err) {
        console.log(cbIndex + ' ' + err);
      }  else {
        console.log(cbIndex + ' exec');
      }
    });
  })(count);

  // call pool.end when arrived 5 
  if (count % 5 === 0) {
    pool.end(function(err) {});
  }

  // stop
  if (count === 10) {
    clearInterval(interval);
  }

  count++;
}, 10);

The result:

The callbacks from 3 to 5 have been pushed into connection queue, but they are not executed.

[dougwilson]

Thanks :) I've identified the issue, and will have it fixed soon. I appreciate you checking that the fixes are actually working for you 👍

[dougwilson]

OK, now the the latest commit 1397f67 your example script is running on the callbacks. Let me know if you find anything else :)

[iammapping]

Great, it works.

[dougwilson]

Awesome to hear 👏 it's even in the new 2.2.0 release, so you can officially have this fix :)