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Re: Objects, processes, and encapsulation

Hi Tom, Ian, Peter, others,

Too bad I missed the conference...

I read Tom's article. It is a very good start!

     The Callback problem can be simplified to something like this:

          "During a call to an external object, any method of the
           original object may be called from externally. The
          state of the original object may therefore have completely
          changed during a single method call."

The callback results in a cyclic call, which causes the problem.
Note that in CSP, such cyclic calls would typically result in deadlock.

     A sends message to B, and waits for response.
     B sends request to A.
     Deadlock: A is waiting for the result, and cannot handle
     the request sent by B.

Cyclic & Synchronous relationships are a problem: in CSP and in OO.

Should they be rulled out? If so, how? If not, how should they be dealt with?


Marcel Boosten           | Philips Medical Systems
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