[eurolisp] Re: http://www.dirkgerrits.com/erlisp/roadmap.html

[Faré]

>>: "Hoehle, Joerg-Cyril" <Joerg-Cyril.Hoehle at t-systems.com>
>: Dirk Gerrits <dirk at dirkgerrits.com>

>> Therefore I was disappointed by your roadmap which talks a lot about
>> OS threads and special (thread-local) variables.
> 
> Sorry to hear that, care to elaborate?
>
After a few tens of thousands of threads (may hundreds of thousands,
on modern machines with several gibibytes of RAM?), the performance of
most (all) Unix kernels becomes very bad. If only because each thread
eats at the very least a few kilobytes of kernel memory, and
ultimately the machine runs out of memory. Green thread have a
potentially much lower overhead.

>   * Using continuations as green threads.  This would limit the points
>     at which processes can be preempted, but that can be partially
>     alleviated by assigning an operating system thread to every few
>     green threads.  Also, less preemption is not necessarily a problem.
>
With sufficient engineering and code-walking, preemption can remain
possible. However, preemption necessitates proper handling of
invariants, with locking, roll-back and/or roll-forward.
As a cheaper way to do things, cooperative multithreading can do, and
can be used automatically or semi-automatically. (Only potentially
long-running routines need have (yield) statements inserted, and with
proper code-walking, this can be done automatically.)

> and a CPS code walker is more work than using an OS thread library.
There already are CPS code walkers, in Screamer and in UCW.

>> Cf. http://c2.com/cgi/wiki?MessagingAsAlternativeToMultiThreading

> http://groups.google.com/groups?selm=87acurudww.fsf%40dirkgerrits.com&rnum=1

> I agree that a better place for discussion is needed.  How about a common-lisp.net mailing list?
If you create it, please subscribe me :)

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