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Date: Sun, 28 Jan 2018 20:00:14 +0000
From: Eric Wong <normalperson@yhbt.net>
To: ruby-core@ruby-lang.org
Message-ID: <20180128200014.GB10749@starla>
References: <redmine.issue-13618.20170601001407@ruby-lang.org>
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 <20180123173133.GB14355@starla> <20180124215113.GA29994@starla>
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Subject: [ruby-core:85189] Re: [Ruby trunk Feature#13618][Assigned] [PATCH]
 auto fiber schedule for rb_wait_for_single_fd and rb_waitpid
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Koichi Sasada <ko1@atdot.net> wrote:
> On 2018/01/25 7:01, Eric Wong wrote:
> >For everything else that serves multiple clients in a single
> >process, fair sharing is preferable.
> 
> Could you elaborate more? Generally, fairness is preferable. But I think we
> can document "we don't guarantee fairness scheduling on this feature",
> because our motivation is to provide a way to process multiple connections.
> Thoughts?

If I write a multi-process server with many long-lived
connections, it's best to balance those connections to mitigate
bottlenecks/problems which exist in each process.  That way, any
slowdown or crash which affects one process only affects
its fair subset of connections.

This is fair sharing across different *nix processes...
Within each process, Threadlets are also round-robin scheduled,
but run until they cannot proceed.

> Or dose it cause live-lock? (no-problem on server-client apps, but
> multi-agents programs seems to cause live locking)

It should not, Threadlet is FIFO for "ready" Fibers;
epoll and kqueue are readiness queues are FIFO internally, too.

Blocking accept() mitigates live-lock/thundering herd across
different processes.  For non-blocking accept(), I will add
EPOLLEXCLUSIVE support.