Concurrent collections

[Milan Straka]

Hi Simon,

> I went to Aleksandar Prokopec's talk about Concurrent Tries at the Scala day earlier this week.  I thought it was pretty cool. Here's the paper.
>
> http://infoscience.epfl.ch/record/166908/files/ctries-techreport.pdf
>
> http://lampwww.epfl.ch/~prokopec/ctries-snapshot.pdf

Nice :)

> Maybe we should have a Haskell version?  Maybe we already do?

I think we do not have any nontrivial concurrent structures
(we have MVar and FIFO + Semaphore built on top of it).

Most of work seem to be done on persistent structures. On that front,
Johan's unordered-containers package implements the hash tries,
which are roughly the described CTries without concurrent updates.

I am not sure it would be worth implementing a structure in Haskell
that is inherently concurrent. For me it was always enough to wrap
a persistent structure in an MVar, so updates are performed sequentially
and accesses can be made in parallel.

Such a structure would probably have to be strict and in an ST monad,
to get a usable and deterministic behaviour.

Any thoughts?

Cheers,
Milan