Policies

 

We have already mentioned the policies that control various aspects of POA behaviour. POA policies do not change over the POA's lifetime. When creating a new POA as a child of an existing POA, policies are not inherited from the parent, but instead each POA is assigned a set of default policies if not explicitely defined.

Thread Policy

 

ORB_CTRL_MODEL

(default)
Invocations are performed as scheduled by the ORB. Potentially, many upcalls are perfomed simultaneously.

SINGLE_THREAD_MODEL

 
Invocations are serialized. At most a single upcall is performed at any time.

Non-reentrant servants should only be activated in POAs with the SINGLE_THREAD_MODEL policy.

As the current version of MICO is not multithreaded, this policy is not yet evaluated.

Lifespan Policy

 

TRANSIENT

(default)
Objects activated in this POA cannot outlive the server process.

PERSISTENT

 
Objects can outlive the server process

Id Uniqueness Policy

 

UNIQUE_ID

(default)
Servants can be activated at most once in this POA.

MULTIPLE_ID

 
Servants can be activated more than once in this POA and can therefore serve more than one object reference.

Id Assignment Policy

 

SYSTEM_ID

(default)
Object Ids are assigned by the POA upon object activation.

USER_ID

 
Upon activation, each servant must be provided with a unique Id by the user.

Servant Retention Policy

 

RETAIN

(default)
The POA maintains a map of active servants (the Active Object Map).

NON_RETAIN

 
The POA does not maintain an Active Object Map.

Request Processing Policy

 

USE_ACTIVE_OBJECT_MAP_ONLY

(default)
To process an incoming request, the object reference is looked up in the Active Object Map only. If no active servant serving the reference is found, the request is rejected, and an OBJECT_NOT_EXIST exception is returned.

USE_DEFAULT_SERVANT

 
The object reference is looked up in the Active Object Map first. If no active servant is found to serve the reference, the request is delegated to a default servant.

USE_SERVANT_MANAGER

 
The object reference is looked up in the Active Object Map first. If no active servant is found to serve the reference, a servant manager is invoked to locate or incarnate an appropriate servant.

Implicit Activation Policy

 

IMPLICIT_ACTIVATION

 
If an inactive servant is used in a context that requires the servant to be active, the servant is implicitely activated.

NO_IMPLICIT_ACTIVATION

(default) 
It is an error to use an inactive servant in a context that requires an active servant.

The Root POA has the ORB_CTRL_MODEL, TRANSIENT, UNIQUE_ID, SYSTEM_ID, RETAIN, USE_ACTIVE_OBJECT_MAP_ONLY and IMPLICIT_ACTIVATION policies.