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>Callbacks are a hook back to the client that can be used to trigger an event in the client application or access a client's services when something happens at the server; the calling application provides an entrypoint that is called by the server. VFP doesn't have a callback mechanism either as a client or server.
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>Spawning == creating.
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>Yes, it's is possible for a single COM Object with multiple threads of execution to simultaneously service requests.
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>It is possible for a VFP MTDLL to operate in a non-blocking fashion, but since there is really only a single thread of execution, if you need to have several identical instance of a method to execute simultaneously, ytou need to use MTS to manage multiple instances of the object. It is possible with the MTDLL for a VFP COM Server with multiple COM interfaces to accept and process calls to different methods simultaneously, but the payoff for this is low - in most cases, interspersing execution will result in a longer total time of execution for multiple simultaneous invocations vs a singel line of execution performing operations serially. The difference is that there may be a perception of faster service by the user if seeral requests are serviced at once, since while the total time of execution is longer, the time to complete any one call may appear shorter because of sequence of execution.

Once again, thanks for spending the time to elaborate on this topic. I appreciate it.