Multiple Sequential Access

       A            B            C
       |            |            |
       o-----       |            |
       |     \      |            |
       |      ------o            |
       |            |            |
       |            o-----       |
       |            |     \      |
       |            |      ------o
       |            |            |
       |            |      ------o
       |            |     /      |
       |            o-----       |
       |            |            |<------Not locked!...
       |            o-----       |
       |            |     \      |
       |            |      ------o
       |            |            |
       |            |      ------o
       |            |     /      |
       |            o-----       |
       |            |            |
       |       -----o            |
       |      /     |            |
       o------      |            |
       |            |            |

A, B and C are objects, and I draw the thread of control of an interaction initiated from A.

If I have this scheme in a sequential program of mine, and I just "distribute" C, there isn't anything anymore which insures that its state is not changed between my two accesses. I.e. I have broken the semantics of my initial program!

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Marc Girod
Last modified: Sat Feb 28 14:26:44 EET 1998