DDS15 — find_topic/delete_topic underspecified

It is not clear what kind of restrictions there are to find_topic/delete_topic.

Assume two software modules in the same process, order of instantiation is not fixed, also more modules could be loaded by a configuration file. All modules use find_topic to find topic Foo, the first module now calls create_topic to create the topic, second module gets topic Foo through find_topic.

Each module now creates its own datareader/datawriters using the topic it retrieved. At the moment the module now ends it cleans the datareader/datawriter it has created and now calls delete_topic. It is not clear what at that moment delete_topic will return for the module that has successfully used find_topic to get the topic. Some DDS vendors return RETCODE_OK, some RETCODE_PRECONDITION_NOT_MET because there are still readers/writers related to that topic (but the other module did use create_topic). The shutdown order can also be swapped, so first the module that used create_topic will be removed, the one with find_topic keeps running.

The description of find_topic should be extended to clarify how it behaves related to delete_topic? Personally I think RETCODE_OK should be returned when there is no DataReader, DataWriter, ContentFilteredTopic, or MultiTopic attached anymore to the topic returned by find_topic, independent of the entities attached to the topic as it was created by create_topic (or a different find_topic call)