Run a device server without a database

Run a device server without a database#

audience:administrators audience:developers

In some cases, for example running a device server within a lab during hardware development, testing, etc, it can be useful to have a device server able to run even if there is no Tango database or File database available in the control system. Note that running a Tango device server without a database means losing some Tango features:

  • There are no checks that the same device server is running twice

  • There is no device configuration via properties

  • There are no memorized attributes

  • There is no device attribute configuration via the database

  • There are no checks that the same device name is used twice within the same control system

  • If several device servers are running on the same host, the user must manually manage a list of network ports alreaady in use

To run a device server without a database, the -nodb command line option for the device server must be used. One problem when running a device server without the database is passing device names to the device server. Within Tango, it is possible to define these device names at two different levels:

  1. At the command line with the -dlist option: In the case of a device server with several device pattern implementations, the device name list given at the command line is only used for the last device pattern created in the class_factory() method. In the device name list, the device name separator is the comma character.

  1. At the device pattern implementation level: in the class inherited from the Tango::DeviceClass class via reimplemntation of the method device_name_factory() (cppTango and PyTango).

Device definition at the command line has higher priority than overriding device_name_factory().

If nothing is passed or set, the device name NoName is used for each device pattern implementation.

Example of a device server started without database usage#

Without a database, you need to start a Tango device server on a pre-defined port, and you must use one of the underlying ORB options called endPoint, i.e.:

server inst -ORBendPoint giop:tcp::<port number> -nodb -dlist a/b/c

This will start the device server executable server as the instance inst on all available network interfaces giving it the device name a/b/c.

Below are two examples of starting a device server without a database - note that in this case the device_name_factory() method has not been re-defined.

  • StepperMotor et -nodb -dlist id11/motor/1,id11/motor/2

    This command line starts the device server with two devices named id11/motor/1 and id11/motor/2

  • StepperMotor et -nodb This command line starts a device server with one device named NoName

Below is an example where the device_name_factory() method has been re-defined within the StepperMotorClass class.

1  void StepperMotorClass::device_name_factory(vector<string> &list)
2  {
3      list.push_back("sr/cav-tuner/1");
4      list.push_back("sr/cav-tuner/2");
5  }

  • StepperMotor et -nodb

    This commands starts a device server with two devices named sr/cav-tuner/1 and sr/cav-tuner/2

  • StepperMotor et -nodb -dlist id12/motor/1

    Starts a device server with only one device named id12/motor/1

Connecting clients to a device within a device server started without a database#

In this case, the host and port on which the device server is running are part of the device name. For example, if the device name is a/b/c, the host is mycomputer and the port is 1234, then the device name to be used by a client is

mycomputer:1234/a/b/c#dbase=no

Some clients, like Atkpanel, require the tango:// prefix:

tango://mycomputer:1234/a/b/c#dbase=no

See device naming for further details on Tango object naming.