Virtual Atomicity (was: purse deposit and the Cambio)
Thu, 24 Jun 1999 18:15:34 -0700 (PDT)
>>One can similarly define E's semantics in terms a hierarchy of such units of
>>* The unit of operation for concurrent distributed computation is the Turn.
>>Because a Turn only has synchronous access within its own Vat, one may
>>faithfully describe overall distributed computation as a globally
>>serializable sequence of atomic Turns, ...
>[-] Not in the face of infinite Turns.
>If Turns really were equivalent to a serializable sequence, no more than one
>Turn could ever go into an infinite loop, and no Turns could be in the
>causal future of that Turn. A single infinite Turn would use up the
>universe's capacity for further computation. In fact, an infinite Turn does
>use up its Vat, but not the universe. Asynchronous messages sent by an
>infinite Turn are delivered and processed as long as their recipient lives
>in another Vat. These other Turns are, by serialization order, "after" an
>infinite atomic Turn.
In the Future, when compute resources are metered must be paid for,
one could arrange a Vat so that no Turn is left unthrowed.
>This is all as it should be. In fact, the block-the-universe consequences of
>true serializability would be pathologically stupid. However, it means more
>formal hair to describe the kind of Turn serializability E provides.
It's hard because you're trying to describe a Universal Turn Machine.