Clarification on Thread Dispatching 5.4.2

[jjhugues]

Submitted on behalf of Danielle Stewart after a joint review of this section with John Hatcliff and Jerome Hugues.

We need to clarify 5.4.2 to build a precise definition of the following concepts

• dispatch guards
• dispatch trigger and set of features that can dispatch a trigger

These definitions are required to elaborate further on the notion of frozen ports in 9.2.4

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• Order of clauses matters. Should first outline definitions such as dispatch and trigger. All else builds from these.
• Define what could trigger a dispatch in a comprehensive list and state explicitly that the dispatch protocol of a thread determines which of these triggers result in dispatch.
• The use of E as a set of events causing dispatch is messy and an element being emptyset or zero makes no sense.
• (31) talks about Dispatch_Trigger, but does not mention that threads make use of it differently based on the dispatch protocol they have. (34) talks about Dispatch_Protocol and perhaps should come before Dispatch_Trigger.
• Group clauses specific to a dispatch protocol together. For instance, all periodic specific clauses together (notice (33) is not grouped with (35), (36)).
• (34) lumps into the Dispatch_Protocol the notions of Enabled function and Wait_For_Dispatch function. Perhaps these should be separate for clarity.
• (35) mentions delta t without previous definition of delta.
• (37) needs to be explicit that this is an exclusive or between options and also should rank in terms of priority. That way if a user does not define a Dispatch_Trigger value on an aperiodic thread, it is absolutely clear what causes dispatch to occur.
• (39) “If multiple ports are involved in triggering the dispatch,…” it is unclear what this means. Is there a case when multiple ports are needed to trigger a dispatch? How? Is it that there are multiple means of triggering, all of which are true, thus the dispatch occurs? But if that was the case, then the first arrival should have triggered it. This is unclear.
• (38, 40-42) all reference a set E and elements in that set. I believe this is the list of things that can trigger dispatch for this thread, but that is not clear. Notation is ambiguous at best.
• (43) “logically simultaneously”: I am not sure what this means in a real time system.
• (45) move a summary table to the point where dispatch protocols are introduced. Could rework this table to include dispatch protocol, dispatch condition (what is the E for this thread), Enabled method, and Wait_For_Dispatch conditions. Would be helpful to have all this info in one place.

[jjhugues]

Section 5.4.2 has been deeply revised

[asazonova]

Consistency rule C1 in AADL standard for threads: AADL reserves the following ports. If defined, they must match the following constraints:

Complete must be an out event port Error must be an out event data port Abort must be an out event port Stop must be an out event port fixes #2652