Method jobTick

lib/queue.js:688–748

()

    this.concurrency = concurrency;

    const jobTick = () => {
      if (this.paused) {
        this.queued -= 1;
        return;
      }

      // invariant: in this code path, this.running < this.concurrency, always
      // after spoolup, this.running + this.queued === this.concurrency
      finally_(
        this._getNextJob().then((job) => {
          // We're shutting down.
          if (this.paused) {
            // This job will get picked up later as a stalled job if we happen
            // to get here. We can't easily process this job because at this
            // point Queue#close has already captured the activeJobs set in a
            // Promise.all call, and we'd prefer to delay a job than
            // half-process it.
            this.queued -= 1;
            return;
          }

          this.running += 1;
          this.queued -= 1;
          if (this.running + this.queued < this.concurrency) {
            this.queued += 1;
            setImmediate(jobTick);
          }

          if (!job) {
            // Per comment in Queue#_waitForJob, this branch is possible when
            // the job is removed before processing can take place, but after
            // being initially acquired.
            return;
          }

          return this._runJob(job).then((results) => {
            this.running -= 1;
            this.queued += 1;

            /* istanbul ignore else */
            if (results) {
              const status = results[0],
                result = results[1];
              this.emit(status, job, result);

              // Workaround for #184: emit failed event for backwards
              // compatibility while affording for a separate event that
              // identifies the final failure.
              const emitExtra =
                status === 'retrying'
                  ? 'failed'
                  : status === 'failed'
                    ? 'failed:fatal'
                    : null;
              if (emitExtra) this.emit(emitExtra, job, result);
            }
          }, this._emitErrorAfterTick);
        }),