fix(worker): allow retrieving concurrency value

[fgozdz]

No description provided.

[manast]

LGTM

[roggervalf]

I think this is a bug where this.opts.concurrency should not be set, instead it should be this.concurrency = concurrency at line 395. opts should be immutable as we threat other options like priority or delay. If you change that line, this getter may not be needed

[fgozdz]

This is resulting in unending recursion: "RangeError: Maximum call stack size exceeded"

[manast]

@fgozdz what @roggervalf means is that we should not replace this.opts.concurrency as this is mutating the opts object which was passed in the constructor. Instead you can define a private property like _concurrency, and use this instead of this.opts.concurrency. In the constructor you set _concurrency to a default value if this.opts.concurrency is not defined.

[manast]

Honestly speaking It would be far mote elegant to have a explicit setter like "setConcurrency" instead of an implicit setter, but this would imply a breaking change, so we cannot do that now.

[roggervalf]

@fgozdz you can try doing:

set concurrency(concurrency: number) {
    if (
      typeof concurrency !== 'number' ||
      concurrency < 1 ||
      !isFinite(concurrency)
    ) {
      throw new Error('concurrency must be a finite number greater than 0');
    }
    this._concurrency = concurrency;
  }

  get concurrency(): number {
    return this._concurrency;
  }

on worker constructor you may need to replace https://github.com/taskforcesh/bullmq/blob/master/src/classes/worker.ts#L241 as:
this._concurrency = this.opts.concurrency;
and add a private attribute type after this one https://github.com/taskforcesh/bullmq/blob/master/src/classes/worker.ts#L182 like:
private _concurrency:number;
also in order to use this new attribute you should replace this.opts.concurrency to use this._concurrency at worker level

[fgozdz]

This issue fixes #2880

[roggervalf]

Lgtm, thank you