Re: [boost] [future] Early draft of wait for multiple futures interface

From: Johan Torp (johan.torp_at_[hidden])
Date: 2008-05-30 12:41:40

Anthony Williams-4 wrote:
> 
>> One problem is wait_for_any is not sufficient to implement an efficient 
>> scheduler.  You have to copy all the futures into wait_for_any so each 
>> wait_for_any call is O(N).  So something like the future_selecter (should
>> be 
>> spelled future_selector?) class I mentioned earlier would still be
>> needed.
> 
> What do you mean by O(N) in this context?
> 
> You have N futures to wait for. You have to somehow register that
> you're waiting for each one => you need O(N) operations.
> 
> I suppose that if one of the futures was already ready, you could skip
> the rest, but that doesn't really strike me as much of an improvement.
> 
> Once it's done registering, wait_for_any then blocks until one of them
> is ready. No polling, just a single wait.
> 
> Could you elaborate on what you were getting at?
> 

I think that it's a common use case to serve or ignore one ready future and
then go back to waiting on the remaining ones. This would requrie O(N^2)
with your interface.

Johan
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