From: Eric Wong <normalperson@yhbt.net>
To: SASADA Koichi <ko1@ruby-lang.org>
Cc: Ruby developers <ruby-core@ruby-lang.org>
Subject: [ruby-core:80531] Re: [ruby-cvs:65407] normal:r58236 (trunk): thread.c: comments on M:N threading [ci skip]
Date: Sun, 2 Apr 2017 02:35:14 +0000 [thread overview]
Message-ID: <20170402023514.GB30476@dcvr> (raw)
In-Reply-To: <8a2b82e3-dc07-1945-55f9-5a474e89130b@ruby-lang.org>
SASADA Koichi <ko1@ruby-lang.org> wrote:
> Hi Eric,
>
> I agree it is possible to use M:N model.
>
> There are several problem mainly because of C extensions (and libraries
> which C extensions use).
>
> 1.We can't move execution context across native threads by userland
> because some libraries can use thread local variables used by
> native thread system.
> Also because some libraries can depends on C-stack layout.
Hi ko1, thank you for response.
Correct, I'm not sure if this can be changed while maintaining
compatibility. Anyways I think I am fine with this limitation
where a Fiber is always tied to a particular native thread.
> 2.Some libraries can stop threads because of uncontrollable
> I/O operations (wait for IO (network) with system calls),
> uncontrollable system synchronization (mutex, semaphore, ...),
> big computation (like mathematical computation).
>
> Current 1:1 thread model does not have such issues (if C extensions
> release GVL correctly), so we employee it.
> However, the overhead of thread creation and thread switching is high,
> as you say.
>
> However, the issues 1 and 2 are *possible* issues. We don't know which
> libraries have a problem. If we only use managed C extensions, there are
> no problem to use M:N mode.
2 is tricky. I think in worst case (no modifying existing C
exts or API), M:N will degrade to current 1:1 model, which
retains 100% compatibility with current Ruby 1.9/2.x code.
> For Ruby 3, Matz want to encourage such fine grain context switching. We
> discussed before and we planed to introduce automatic Fiber switching at
> specific I/O operation. It is small version of your proposal, it is one
> possibility (and it is easy than complete M:N model). I'll change Fiber
> context management to lightwieght switching for Ruby 2.5 and try it at
> later versions.
Cool! I was thinking along the same lines. I think Ruby Thread
class can become a subclass of Fiber with automatic switching.
However, to spawn native threads:
If a Thread uses existing GVL release C-API, then the _next_
Thread.new call will create a native thread (and future
Thread.new will be subclass of Fiber in new native thread).
So, in pseudo code:
class Thread < Fiber
def self.new
case Thread.current[:gvl_state]
when :none
# default
super # M += 1
when :released
# this is set by BLOCKING_REGION GVL release
# only allow a user-level thread to spawn one new native thread
Thread.current[:gvl_state] = :spawned
NativeThread.new { Thread.new } # N += 1
when :spawned
# We already spawned on native thread from this user-level
# thread, only spawn new user-level thread for now.
super # M += 1
end
end
end
Current GVL release operations will change
Thread.current[:gvl_state] from :none -> :released
next parent reply other threads:[~2017-04-02 1:58 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170402011414.AEA9B64CEE@svn.ruby-lang.org>
[not found] ` <8a2b82e3-dc07-1945-55f9-5a474e89130b@ruby-lang.org>
2017-04-02 2:35 ` Eric Wong [this message]
2017-04-02 3:05 ` [ruby-core:80532] Re: [ruby-cvs:65407] normal:r58236 (trunk): thread.c: comments on M:N threading [ci skip] SASADA Koichi
2017-04-03 4:42 ` [ruby-core:80540] " Eric Wong
2017-05-08 0:33 ` [ruby-core:81027] " Eric Wong
2017-05-08 1:53 ` [ruby-core:81028] " SASADA Koichi
2017-05-08 2:16 ` [ruby-core:81029] " SASADA Koichi
2017-05-08 3:01 ` [ruby-core:81031] " Eric Wong
2017-05-08 3:42 ` [ruby-core:81033] " SASADA Koichi
2017-05-08 6:36 ` [ruby-core:81035] " Eric Wong
2017-05-09 2:18 ` [ruby-core:81042] " SASADA Koichi
2017-05-09 3:38 ` [ruby-core:81044] " Eric Wong
2017-05-09 4:11 ` [ruby-core:81045] " SASADA Koichi
2017-05-09 5:12 ` [ruby-core:81047] " Eric Wong
2017-05-09 5:47 ` [ruby-core:81049] " SASADA Koichi
2017-05-09 6:23 ` [ruby-core:81053] " Eric Wong
2017-05-09 6:44 ` [ruby-core:81054] " SASADA Koichi
2017-05-09 18:51 ` [ruby-core:81078] " Eric Wong
2017-05-10 3:24 ` [ruby-core:81083] " SASADA Koichi
2017-05-10 10:04 ` [ruby-core:81089] " Eric Wong
2017-05-19 4:34 ` [ruby-core:81244] " Eric Wong
2017-06-20 19:16 ` [ruby-core:81733] " Eric Wong
2017-05-09 5:54 ` [ruby-core:81050] " SASADA Koichi
2017-05-09 6:15 ` [ruby-core:81052] " Eric Wong
2017-05-08 2:56 ` [ruby-core:81030] " Eric Wong
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