[higgins-dev] [IdAS] Context open/close semantics

[Greg Byrd <gbyrd@xxxxxxxx>]

Based on previous discussions, we need to clarify what it means to open 
and close a Context.  Here's a whack at it.

(1) An open Context represents a binding between a client (specified by 
the identity in the open() call) and the data published by the Context.  
There is no API for determining the identity of the client that opened a 
Context.

(2) The following Context methods require a Context to be open: 
getSubject, getSubjects, createSubject, removeSubject, 
verifySubjectAttributes, updateSubject, exportData, importData.  Calls 
to these methods on a non-open Context will result in a 
IdASContextNotOpenException.  An implementation may choose to verify 
that the calling entity is authorized (e.g., by using JAAS getSubject on 
the executing thread).

(3) I propose that open return an IContext, rather than void.  If a 
Context is not open, then open may return that same Context object.  If 
the Context is already open, a new IContext may be returned that 
represents this new association between another client and the data.  
Alternatively, an implementation may choose to return the same object if 
multiple bindings are not supported.  (This effectively performs a 
close, then an open on the same object.)

(4) The close operation returns the Context instance to an unopened 
state, as if the Context were newly-created.