code: function SetCrontab (gateway, inactivity) {
      // let's call back ourself after inactivity*1000/4
      gateway.Debug (5, "SetCrontab inactivity=%d", inactivity);
      setTimeout (function(){SetCrontab (gateway, inactivity);}, inactivity*250);
      
      // let compute inactivity timeout limit
      var timeout = new Date().getTime() - (inactivity *1000);
      
      for (var devid in gateway.activeClients) {
          var device = gateway.activeClients[devid];
          if (device.lastshow < timeout) {
              gateway.Debug (1, "Removed ActiveDev Id=%s uid=%s", device.devid, device.uid);
              delete gateway.activeClients [devid];
          }
      }
        
  }
docs: 30s in between two retry this function scan active device table and remove dead one based on inactivity timeout