Ed, (01)
I completely agree: (02)
> In the more general case, two or more processes are "asynchronous"
> if they are simultaneously "enabled" (allowed to start) but their
> actual start times may depend on other events. (And "enabled" is
> a state, not an action, although it may result from an action; some
> (autonomous) processes are always enabled.) They may run concurrently
> and along the way they may produce "broadcast signals" or "directed
> signals" that enable other processes in the set to determine that
> some state of the overall world has been achieved. Starting and
> coming to an end are just some of those states. And such processes
> may then also "wait" at some point in their own activity sequence
> for the receipt of such a signal from a sibling process. Some
> engineers speak of these "waits" as "synchronization points"; others
> would argue that they are only really "synchronizations" if there
> is an exchange of signals that confirms that all the relevant
> processes have reached the same point before any of them continues. (03)
Unfortunately, it is very hard to explain all those abstract points.
The reason why I like Petri nets is that you can illustrate each
of those points with very simple, clearly understandable diagrams. (04)
Actually, I use moving diagrams. In the days of overhead projectors,
I used plastic sheets with unmarked circles for the states. Then I
brought in my collection of tokens (which I kept in a Petri dish)
and moved them along nodes of the of the net. (I bought my tokens
in Germany -- for one pfennig each. Too bad that they no longer
have pfennige.) (05)
I still find the plastic sheets and movable tokens more effective
than any computer aids. (06)
John (07)
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