Re: [boost] [afio] Formal review of Boost.AFIO

On 9/1/2015 11:43 AM, Giovanni Piero Deretta wrote:

On 1 Sep 2015 2:15 pm, "Agustín K-ballo Bergé" wrote:

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On 9/1/2015 9:35 AM, Giovanni Piero Deretta wrote:

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On 30 Aug 2015 10:04 pm, "Agustín K-ballo Bergé" wrote:

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The situation gets trickier for `wait_for/until`, where you need to

remove

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the fake continuation on a timeout without racing.

Also needed to implement wait any.

Once `wait` returns the shared-state is ready. You don't even need to remove the fake continuation pointer, it will never be looked up again.

You do if you want to implement a wait_any interface that blocks until the first of a number of futures is ready. In that case you must be able to reissue another wait at a later time. Think 'select'.

I did not understood what you meant by "wait any" the first time around. I do now, but I still don't see why would you ever want to wait on an already ready future. If you do, it would just return immediately; it should not even touch callbacks, continuations, condition variables, etc.

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A dismissible, efficiently implementable

'then' protocol could be the key for future composition across libraries. I would prefer if in this case the continuation were pointer sized to allow lock free implementations.

I don't think pointer sized continuations would buy you anything, you can attach multiple continuations to a single shared-state (via `shared_future`) so you will always end up needing memory allocation eventually. That doesn't stop you from attaching the pointer to the continuation decayed-copy in a lock free way.

Only if you use shared state. I'm looking at optimising unique futures. My shared future implementation currently is internally N unique futures plus a multiplexer.

You always have a shared state (the concept, in one form or the other), it is part of the specification of the semantics.

Also for waits you can always allocate the waiter/signaler on the stack. The tricky part is handling the race between a dismissal and a signal.

This is exactly the trickiness I was referring to for `wait_for/until` vs `wait`.

To implement the generic 'then' I do always heap allocate, but I put the callback inline with the returned future shared state. I use the pointer sized dismissible 'then' to chain the two shared states.

Nod, and after the allocation you can attach the pointer to the callback in a lock free way. You can further chain multiple continuations for a `shared_future` in a similar way. Regards, -- Agustín K-ballo Bergé.- http://talesofcpp.fusionfenix.com