activate(context) {
    if (context.activated) { return; } // prevent double activation
    context.activated = true;
    context.deactivated = false;
    this.load += 1;
    this.emit('activate', this.load);
    if (this.ordered || this.autoOrdering) {
      this.outputQ.push(context.result);
    }
  }
@param {Object} context
@param {boolean} context.activated
@param {boolean} context.deactivated
@param {Object} context.result