View source for Agents in SCOOP

The page reflects current decisions taken for the current SCOOP implementation, in particular without support for processor tags. So it may change in the future.

== Status of agent targets ==
: Because any agent object is created on a processor associated with the agent's target, that target hasto be controlled.
'''Agent target validity rule.''' The target of an agent must be controlled.

== Types ==
'''Agent argument types validity rule.''' If an agent has a separate target, every non-expanded argument of the associated feature must be separate.
: Because an agent is created on a processor of a target, without processor tags it is impossible to create an agent on an open target of separate type and then pass the corresponding target object at the agent call. Also there is no way to make an open target controlled (see previous rule).
'''Agent open target type validity rule.''' If the target of an agent is open, it may not be separate.

'''Example.''' <e>
f (p: separate P; q: separate Q): R
t: separate T
...
r := agent t.f (c, ?)
x := r.item ([a])
</e>
The type <e>t</e> of <e>agent t.f (c, ?)</e> is <e>
      separate FUNCTION [ANY, TUPLE [separate Q], separate R]
</e>

: The first parameter is not separate because both a target and an agent object run on the same processor.
: The separateness status of the type <e>TUPLE</e> used for arguments does not matter, what matters is the types of arguments. In many cases when <e>TUPLE</e> is used, it is used as a value type, i.e. it could even be an expanded type, so that a separate mark is not required. But then we need some conversion rules to attach different types of <e>TUPLE</e>. In order to avoid unnecessary processor dependency, it's going to be created on the target processor (as a routine object itself), therefore it is not <e>separate</e>.

== Agent classes ==
The first parameter in the class <e>ROUTINE</e> and descendants is not used, so in the future it will be dropped altogether.

'''Example.''' The agent type from the example above becomes<e>
      separate FUNCTION [TUPLE [separate Q], separate R]
</e>

== Correctness and wait conditions ==
The feature <e>{ROUTINE}.precondition</e> should be split into 2 parts: <e>correctness_condition</e> and <e>wait_condition</e>. Then the routine <e>call</e> looks like<e>
      call (a: OPEN_ARGS)
          require
              correctness_condition (a)
          do
              from
              until
                  not wait_condition (a)
              loop
                  execute_body (a)
              end
          end
</e>
The same change applies to the feature <e>item</e>.