[e-lang] Looser memoization and constant-folding: will this work?

[Bill Frantz]

kpreid at mac.com (Kevin Reid) on Tuesday, July 25, 2006 wrote:

>On Jul 23, 2006, at 0:41, Mark S. Miller wrote:
>
>> ... If the computation exceeds its budget, the E-to-CL  
>> compiler could preemptively terminate it, in violation of the  
>> general E model. This would be safe since a partially completed  
>> DeepFrozen-returning-DeepFrozen computation cannot leave behind any  
>> reachable residual side effects.
>>
>> Is this reasoning sound? Is it really safe to preemptively  
>> terminate such
>> computation?
>
>No. Consider what happens if one of the previously-discussed  
>DeepFrozen memoizers is in the process of updating its hash table,  
>within the speculative execution, at the moment you interrupt it.

I assumed that preemptive termination consisted of blowing the vat away
and restarting that vat from its last checkpoint.  That procedure would
also return th DeepFrozen memoizer to a consistent state.

Cheers - Bill

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