Re: [Caml-list] Multicore runtime

[Stephen Dolan <stephen.dolan@cl.cam.ac.uk>]

On Sun, Sep 7, 2014 at 10:47 PM, Jiten Pathy <jpathy@fssrv.net> wrote:
> Hello,
> Nice work by stephen et al. on multicore runtime. Just had some questions:-
> 1. What's the mapping between os threads and domains?

One-to-one.

> 2. How does blocked fibers on a domain work? Does a blocked os thread
> running a fiber creates new os thread for that domain?

Fibers blocked on internal events (e.g. waiting for another fiber to
fill in an mvar) don't block anything - the system just runs some
other fiber. Fibers blocked on long-running / blocking C calls do
block the domain. If they do so for long enough, other fibers on the
domain will be moved to active domains.

Generally, we're going to try to avoid blocking C calls and instead
use select/poll/kqueue/epoll to handle blocking I/O. From the fiber's
point of view, this looks like normal blocking I/O, except if a system
call returns EWOULDBLOCK we'll switch to another fiber until the I/O
is ready.

> 3. Is there anyway for a fiber to relinquish a domain, for the ones
> that do loops for a significant period of time without blocking other
> fibers?

There's a yield function that can be called explicitly. Currently,
compute-bound fibers that don't yield do tie up a domain.

Stephen