ISSUE 98: Scopes and component instances

[Bryan Aupperle <aupperle@us.ibm.com>]

These are what I believe are the general
principles that we have concluded (and some implications of them) in our
discussions.  If there are no major disagreements, I will start working
on some draft spec changes.

For C++:

• There are three scopes
  •  Stateless: Single threaded, Conceptually a new instance for each function invocation. Use of statics or global variable access break model but cannot be prevented by runtime.  Data members OK, but cannot be counted across function invocations.
  •  Client (default): Single threaded, A new instance for each distinct client instance. Use of statics or global variable access break model but cannot be prevented by runtime.  Data member values are maintained between function invocations from the same client instance.
  •  Composite: Multi threaded, One instance for life time of composite.  Statics and global variable access OK if domain level composite, for other composites, statics and global variables can result in unindented data sharing.  Data members OK.
• The runtime does no synchronization
• Library is loaded when composite using a component implementation in the library is placed in running state.
• Eager initialization means object created when composite using component implementation is placed in running state.
• Implementations cannot assume a library is ever unloaded.

For C:

• No scopes
• Need to allow properties to be local variables (multiple local variables with function of one implementation are OK if either different names - different properties - or same names and types - one property, same name and different types is an error).
• The runtime does no synchronization
• Library is loaded when composite using a component implementation in the library is placed in running state.
• Eager initialization means object created when composite using component implementation is placed in running state.
• Init and destroy function of an implementation can be multiple time is the implementation is used for components in multiple composites.
• Implementations cannot assume a library is ever unloaded.

Bryan Aupperle, Ph.D.
STSM, WebSphere Enterprise Platform Software Solution Architect

Research Triangle Park,  NC 
+1 919-254-7508 (T/L 444-7508)
Internet Address: aupperle@us.ibm.com