docs: function(callback) {
          if (this._isShuttingDown || this._isStartingUp) {
              return;
          }
  
          this._isShuttingDown = true;
  
          // See if the app is running.
          if (!this.processId() && !this.sideProcessId()) {
              this._isShuttingDown = false;
              // Nope, not running.
              if (callback) {
                  callback();
              }
  
              return;
          }
  
          // Kill the app.
          clearTimeout(this._restartTimeout);
          this._appProcess.kill();
          if (this._sideProcess) {
              this._sideProcess.kill();
          }
  
          // Check on an interval to see if it's dead.
          var check = setInterval(_.bind(function() {
              if (this.processId() || this.sideProcessId()) {
                  return;
              }
  
              clearInterval(check);
              logger.info('App shut down by force.');
              this._isShuttingDown = false;
              if (callback) {
                  callback();
              }
          }, this), 250);
      }