Virtual Atomicity (was: purse deposit and the Cambio)

[Chip Morningstar]

MarkM says:
>>One can similarly define E's semantics in terms a hierarchy of such units of 
>>operation.
>>...
>>* 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.