DSS2 — Section 9.1.7: Convey Region Designator Sets Switch: copies conveyed

As currently stated, the standard says that designators of region realizations are conveyed in conveyed region sets. However, the conveyed region sets must contain designators of copies of region realizations, rather than designators of region realizations themselves, because if the designators of the actual region realizations were to be conveyed, this would result in an undesirable race condition. If the designators were of actual region realizations, for example, rather than of just copies of region realizations, then after a federate invokes an Update Attribute Values service or a Send Interaction with Regions service that results in a set of sent region designators being conveyed in the corresponding Reflect Attribute Values † service or Receive Interaction † service, there is a race that could occur between the federate that sent the update or interaction setting new range bounds and committing region modifications to a sent region, and the federate that received the reflect or interaction invoking the Get Dimension Handle Set and Get Range Bounds services to query all of the range bounds of the region realization received.

According to post-condition (b) of the Commit Region Modifications service, when a region specification is modified, all update region realizations that are derived from that region specification are also modified. If the updating federate modifies the conveyed region realization before the reflecting federate has a chance to use the Get Range Bounds service to determine what the range values of each dimension of the sent region realization were, then the reflecting federate will never be able to determine what the range values of the region realization were when the overlap calculation that resulted in the reflect was performed. A race condition would exist between the updating federate's attempt to modify the region specification and the reflecting federate's attempt to determine the range values of each dimension of the derived region realizations received.

Conveying designators of copies of these region realization, instead of designators of the region realizations themselves, eliminates this race condition. The reflecting federate is always guaranteed that if it queries the range bounds using a region designator conveyed in a reflect or received interaction while the reflect or receive interaction is still in progress, the range values of the region specification copy will be the values of the update region realization that were in effect at the time that the overlap calculation was done on the update region set and subscription region set that resulted in that reflect or received interaction.

The text should be amended to make clear that the set of sent region designators conveyed are not a set of designators of region specifications or a set of designators of region realizations. They are, instead, a set of designators of copies of the update region realizations. The range values of each of the dimensions in each of these region realization copies are the same as the range values of each of the dimensions of the corresponding update region realization that were in effect when the region overlap calculation was performed. Each designator is guaranteed to refer to a particular region realization copy, and the copy is guaranteed to remain in tact, until the Reflect Attribute Values † service or the Receive Interaction † service invocation at the receiving/reflecting federate completes. No change to the range values of the region realization from which the copy was made will cause a change to the range values of the copy as long as the Reflect Attribute Values † service or the Receive Interaction † service invocation is still in progress.

Add the suggested clarifying text.