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

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-06-05 17:20:10

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On Monday 02 June 2008 04:54 am, Johan Torp wrote:
>
> Great, thanks for the effort. Could you post the code somewhere or mail it
> to me at johan [.] torp [at] gmail [.] com? I've been worried that an
> "ideal" future will need to hold a lot of state and becomes somewhat
> complicated.
>

I've committed it to the changes to libpoet cvs now.  I've got future_selector 
implemented, and it seems to work.  I haven't completely converted my own 
scheduler over to properly using it.  I've done some testing, but no 
benchmarking.  

My implementation has become a bit complicated, somewhat more so than 
absolutely necessary.  It boils down to 2 essential things I had to add to my 
future implementation in order to run all user code in future-waiting 
threads, and wait efficiently.

1) I added an event queue for a future, which any thread can push functors 
onto, but only future-waiting threads which call 
future::get/ready/has_exception will cause the functors to be popped off and 
run.

2) For efficiency, I added a signal which is emitted whenever a functor is 
pushed onto a event queue.  The signal publishes another event which 
interested observers can push onto their own event queue.  When the event is 
run, it simply polls the event queue that originally emitted the signal.  
This allows a future which is waiting on N dependencies to only poll the 
event queues which might actually contain events, instead of having to poll 
all N of them every time.
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