Programming CORBA with Orbacus on Linux

POA creation and usage

Getting a root POA

Before creating own POAs, a reference to a root POA must be found. This can be done by resolving the initial service named "RootPOA" as follows:

PortableServer::POA_var rootPOA;
try {
  CORBA::Object_var obj = orb->resolve_initial_references("RootPOA");
  if (CORBA::is_nil(obj)){
    // handle this error
  }
  rootPOA = PortableServer::POA::_narrow(obj);
  if (CORBA::is_nil(myPOA)){
    // handle this error
  }
} catch (const CORBA::ORB::InvalidNames& e){
  // "RootPOA" was invalid, should not occur
} catch (const CORBA::SystemException& e){
  // something else was wrong
}

An example of getting a root POA is given here.

Activation of POAs

Every POA must be activated before it can process requests (meaning dispatching requests to the CORBA objects and servants it manages). Even the default POA, called the root POA, in the simplest server programs must be activated by a method of its corresponding POA manager:

PortableServer::POAManager::activate();

PortableServer::POA_var rootPOA = <get root POA as above>;
PortableServer::POAManager_var manager = rootPOA->the_POAManager();

// activate POA manager
manager->activate();

An example of activating a root POA is given here.

Creation of POAs

If you have a reference to a root POA, you can use it for the creation of your own POA. Typically, you do this if you need POAs with special policies. The creation of a new POA is done with the method

PortableServer::POA_ptr 
  PortableServer::POA::create_POA(<newPOAname>, <POAmanager>, <policies>)

The method may return a nil reference and raise some exceptions, so a typical usage is as follows:

PortableServer::POA_var rootPOA = <get root POA as above>;

PortableServer::POA_var myPOA;
PortableServer::POAManager_var myPOAManager;
try {
  CORBA::PolicyList policies;
  policies.length(2);
  policies[0] = rootPOA->create_id_assignment_policy(PortableServer::USER_ID);
  policies[1] = rootPOA->create_lifespan_policy(PortableServer::PERSISTENT);

  myPOAManager = rootPOA->the_POAManager();
  myPOA = rootPOA->create_POA("MyPOA", myPOAManager, policies);
  if (CORBA::is_nil(myPOA)){
    // handle this error
  }

  // activate POA manager
  myPOAManager->activate();

  <>use new POA for interesting things>
} catch (const PortableServer::POA::AdapterAlreadyExists& e){
  // this POA already exists
  try {
    myPOA = rootPOA->find_POA("MyPOA", 0);
  } catch (const PortableServer::POA::AdapterNonExistent&){
    // strange
  }
} catch (const PortableServer::POA::InvalidPolicy& e){
  // the choosen policy combination is invalid
}

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