It may well be much too early to say, but is there a chance that the
planned move to Chez will result in fewer operations blocking futures? From
what I read of the plans (
https://groups.google.com/d/msg/racket-dev/2BV3ElyfF8Y/UaHcKAHcCAAJ):
>
> Chez exposes OS-level threads with limited safety guarantees. An
> implementation of futures can probably take advantage of threads with
> thread-unsafe primitives wrapped to divert to a a barrier when used in a
> future.
> In other words, while we made futures work for Racket by ensuring that various
> future-safe primitives specifically cooperate, it looks like we can do
> the opposite on Chez: wrap future-unsafe primitives specifically. If that
> works, no changes are needed to Chez.



-Philip

On Tue, Sep 12, 2017 at 9:57 AM, Matthias Felleisen <matth...@ccs.neu.edu>
wrote:

>
> A word of caution on parallelism in general. Not too long ago, someone in
> CS at an Ivy League school studied the use of parallelism across different
> uses and applications. The goal was to find out how much the ‘hype’ about
> parallelism affected people. My recollection is that they found close to 20
> projects where professors (in CE, EE, CS, Bio, Econ, etc) told their grad
> students/PhDs to use parallelism to run programs faster. They checked all
> of them and for N - 1 or 2, the projects ran faster once the parallelism
> was removed. Significantly faster.
>
> People routinely underestimate the communication cost that parallelism
> introduces.
>
> ;; - - -
>
> A word on futures. As James said, they work as advertised but if you do
> read the fine print, you need to understand that in Racket, too many
> operations block futures.
>
> This obstacle will require a decent amount of labor on run-time system.
>
> Even if we overcame this obstacle, we would soon run into others that
> people in the 80s and 90s encountered and addressed with various techniques
> (work stealing load balancing etcetc). We would need to implement all of
> this to catch up and provide a sufficient degree of convenience for futures.
>
> Then it would be *really good thing* for Racket programmers and would even
> turn into a research project.
>
> PRs welcome.
>
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