_addedScriptHashesCleanInterval is not always cleared on redis.quit()

[trentm]

Hi. I believe 3b22f8f added a bug where the new this._addedScriptHashesCleanInterval = setInterval(...) (3b22f8f#diff-d3d9763dec19cf3dd977c437e0be3e6068b13161ee5a2b9b0bf225bddd2d83f8R188) isn't cleared via clearInterval() in all cases. This results in a dangling active handle that will hang a node process.

Here is a repro:

var Redis = require('.'); // ioredis
var redis = new Redis();
redis.on('ready', function () {
    console.log('ready');
    redis.quit();
    console.log('done');
});

% node hang.js
ready
done
<hangs here>

or with ioredis debug output:

% DEBUG=ioredis:* node hang.js
  ioredis:redis status[localhost:6379]: [empty] -> connecting +0ms
  ioredis:redis status[127.0.0.1:6379]: connecting -> connect +6ms
  ioredis:redis write command[127.0.0.1:6379]: 0 -> info([]) +2ms
  ioredis:redis status[127.0.0.1:6379]: connect -> ready +4ms
ready
  ioredis:redis write command[127.0.0.1:6379]: 0 -> quit([]) +1ms
done
  ioredis:redis status[127.0.0.1:6379]: ready -> close +3ms
  ioredis:connection skip reconnecting since the connection is manually closed. +0ms
  ioredis:redis status[127.0.0.1:6379]: close -> end +1ms
<hangs here>

This does not happen if one uses redis.disconnect() instead of redis.quit().

When calling redis.quit(), the closeHandler (in event_handler.ts) is called with self.manuallyClosing == true which does not call the clearInterval added to Redis.prototype.disconnect().

Some options I see (though I am not very familiar with ioredis, so I'm definitely happy to be overriden):

1. Add this._addedScriptHashesCleanInterval.unref() (https://nodejs.org/api/timers.html#timers_timeout_unref) to the connect method. That'll prevent node from hanging, but will persist the setInterval after a program is presumably finished with the ioredis session.
2. Refactor the use of the closeHandler to explicitly call clearInterval.
3. Refactor access to this._addedScriptHashes so that it doesn't require a setInterval to clear it. E.g. perhaps something like https://github.com/isaacs/node-lru-cache using its maxAge option.

[AVVS]

@ShogunPanda could you take a stab at fixing this?

[ShogunPanda]

@AVVS Sure. Tomorrow (CET) I will take a look!

[ShogunPanda]

@AVVS Fixed in #1219 :)