pickWorker() {
        let worker = this.workersQueue.find(worker => worker.canAcceptWork() && worker.isProcessAlive);

        if (this.canStartWorker() && (!this.options.lazyStart || !worker)) {
            this.startWorker();
        }

        if (worker) {
            this.workersQueue.requeue(worker);
            return worker;
        }
    }
Gets the next available worker.

@private
@returns {Worker}