whenCurrentJobsFinished initializes bclient unnecessarily

[gabegorelick]

Description

Bull typically does a good job of lazily connecting to Redis. But the following code causes the blocking client to be initialized unnecessarily:

bull/lib/queue.js

Lines 1140 to 1147 in c0ee6be

	Queue.prototype.whenCurrentJobsFinished = function() {
	return new Promise((resolve, reject) => {
	//
	// Force reconnection of blocking connection to abort blocking redis call immediately.
	//
	const forcedReconnection = redisClientDisconnect(this.bclient).then(() => {
	return this.bclient.connect();
	});

If bclient hasn't been initialized yet, then we're connecting for no reason.

Minimal, Working Test code to reproduce the issue.

const Queue = require('bull');
const Redis = require('ioredis');

const queue = new Queue('foo', {
  createClient (type) {
    if (type === 'bclient') {
      // enforce that we don't waste connections for read-only queues
      throw new Error('This queue is read-only');
    }

    return new Redis();
  }
});
queue.whenCurrentJobsFinished();

Bull version

develop branch

Additional information

Also reproducible when calling queue.pause(true) since that calls whenCurrentJobsFinished internally. Workaround for that is to call queue.pause(true, true) so that whenCurrentJobsFinished is not called. But that only works if you're sure there are no jobs to wait for.