Using Servant Locators

What is a Servant Locator?

When creating a new POA, the application developer may declare specific policy choices for the new POA and provide a different adapter activator and servant manager (these are callback objects used by the POA to activate POAs on demand and activate servants). Creating new POAs also allows the application developer to partition the name space of objects, as Object Ids are interpreted relative to a POA. Finally, by creating new POAs, the developer can independently control request processing for multiple sets of objects.

A Servant Activator is a type of Servant Manager. Servant Managers are optional. You would use a servant manager to allow the POA to activate servants on demand when a request for an inactive object is received. If your server loads all objects when it starts up, you do not need a servant manager.

A servant manager is a callback object that the application developer can associate with a POA. The ORB will invoke operations on servant managers to activate servants on demand, and to deactivate servants. Servant managers are responsible for managing the association of an object reference (as characterized by its Object Id value) with a particular servant, and for determining whether an object reference exists or not. Each servant manager type contains two operations, the first called to find and return a servant and the second to deactivate a servant. The operations differ according to the amount of information usable for their situation.

To use servant managers, the USE_SERVANT_MANAGER policy must be set. Once set, the type of servant manager used in a particular situation depends on other policies in the POA. The two types of servant managers are:

An Example Using Servant Locators

**In progress, please check back for updates!

The following example code shows an application that uses Servant Locators to enable the POA to activate transient objects. This application builds on the "Hello World" example. The following files are included for your information:




Running the Example Servant Activator Example

To run this example,

  1. Create the files using the code shown above.
  2. Run the example as shown in runSample.

You will see output generated to the terminal window similar to that below:

Further Information

For more information on Servant Locators, see the section on Servant Managers in section 11.3.4 of the CORBA 2.3.1 Specification.

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