[ANN] socket_dontwait - socket methods using MSG_DONTWAIT and more

[ANN] socket_dontwait - socket methods using MSG_DONTWAIT and more

[Eric Wong]

This library is a drop-in replacement that reimplements several IO
methods with replacements using MSG_DONTWAIT for BasicSocket.  This
allows us to avoid unnecessary system calls and GVL bouncing.

* http://bogomips.org/socket_dontwait/
* rainbows-talk-GrnCvJ7WPxnNLxjTenLetw@public.gmane.org
* git://git.bogomips.org/socket_dontwait.git

Reports of performance differences with and without this library loaded
would be greatly appreciated!  Feel free to email me privately if you're
shy, too.  HTML mail will be mercilessly deleted :P

The rest of the README below:

We've reimplemented the +readpartial+, +read_nonblock+,
+write_nonblock+, +read+ and +write+ instance methods normally inherited
from the IO class directly into BasicSocket with socket-specific system
calls and flags.

This library is only intended for Ruby 1.9 and will not build with other
versions of Ruby.  This only supports operating systems with the
non-POSIX MSG_DONTWAIT flag for send(2) and recv(2) syscalls.

This library is considered EXPERIMENTAL.  If successful, we'll see about
getting them integrated into the standard Ruby socket library.

== Features

* Avoid use of fcntl(2) to set O_NONBLOCK in favor of MSG_DONTWAIT when
  using non-blocking I/O.  We _unset_ O_NONBLOCK if we need to block
  and release the GVL instead of relying on select(2).

* Avoids select(2) entirely in favor of blocking I/O when the
  GVL is released.  This allows using file descriptor numbers higher
  than 1023 without overflowing select(2) buffers.

* BasicSocket#read uses recv(2) with MSG_WAITALL to avoid extra system
  calls for larger reads.

* Thread and signal-safe, releases the GVL for all blocking operations
  and retries if system calls are interrupted.

* Includes a 1.9.1-specific workaround to preserve errno after reacquiring
  the GVL.  This is
  {fixed}[http://redmine.ruby-lang.org/repositories/diff/ruby-19?rev=27401]
  in newer versions of Ruby.

* Falls back to line-buffered IO if needed (not recommended).

== Bugs/Caveats

* We ignore taint/$SAFE checks, we'll support it if there's demand,
  but we doubt there is...

* Does not support 1.9 encoding filters.  1.9 defaults all sockets to
  Encoding::BINARY anyways, so this should not be noticeable to code
  that leaves socket encodings untouched.

* Does not support write buffering in userspace.  Ruby defaults all
  sockets to "IO#sync = true", anyways so this does not affect code
  that leaves the default setting untouched.

* Avoid using line-buffered IO on sockets (IO#gets, IO#each_line),
  nearly all of the features of this library are cancelled out when
  the line-buffering fallback is used.

== Install

If you're using a packaged Ruby distribution, make sure you have a C
compiler and the matching Ruby development libraries and headers.
You need Ruby 1.9 to install socket_dontwait.  Previous versions of
Ruby will NOT be supported.

If you use RubyGems:

    gem install socket_dontwait

Otherwise grab the latest tarball from:

http://bogomips.org/socket_dontwait/files/

Unpack it, and run "ruby setup.rb"

== Development

You can get the latest source via git from the following locations:

  git://git.bogomips.org/socket_dontwait.git
  git://repo.or.cz/socket_dontwait.git (mirror)

You may browse the code from the web and download the latest snapshot
tarballs here:

* http://git.bogomips.org/cgit/socket_dontwait.git (cgit)
* http://repo.or.cz/w/socket_dontwait.git (gitweb)

Inline patches (from "git format-patch") to the mailing list are
preferred because they allow code review and comments in the reply to
the patch.

We will adhere to mostly the same conventions for patch submissions as
git itself.  See the Documentation/SubmittingPatches document
distributed with git on on patch submission guidelines to follow.  Just
don't email the git mailing list or maintainer with socket_dontwait
patches.

== Contact/Bug Reports/Feedback/Patches/Pull-Requests

This was originally created for the Rainbows! project (but may be used by
others), so we'll reuse their mailing list at
{rainbows-talk-GrnCvJ7WPxnNLxjTenLetw@public.gmane.org}[mailto:rainbows-talk-GrnCvJ7WPxnNLxjTenLetw@public.gmane.org].

-- 
Eric Wong
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Re: [ANN] socket_dontwait - socket methods using MSG_DONTWAIT and more

[Eric Wong]

Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org> wrote:
> This library is considered EXPERIMENTAL.  If successful, we'll see about
> getting them integrated into the standard Ruby socket library.

I've been running socket_dontwait for a few days now with real traffic
(and thus unreliable and slow clients) and haven't noticed anything
wrong.  No crashes, corrupted data, nor fires :)

In synthetic benchmarks, I've seen a ~3-4% performance improvement with
small responses (<= 4K) due to the reduction of syscalls but nothing
measurable with real traffic (which varies a lot and doesn't even come
close to saturating the machines).

-- 
Eric Wong
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[PATCH (socket_dontwait)] README: update with support status

[Eric Wong]

Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org> wrote:
> Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org> wrote:
> > This library is considered EXPERIMENTAL.  If successful, we'll see about
> > getting them integrated into the standard Ruby socket library.
> 
> I've been running socket_dontwait for a few days now with real traffic
> (and thus unreliable and slow clients) and haven't noticed anything
> wrong.  No crashes, corrupted data, nor fires :)

Everything is still good as long with this as long as penguins are
powering your apps :)  Maybe there are other OSes with complete
MSG_DONTWAIT support (and works with Ruby).  Let us know if there
are.

>From 53f39821dfc86c4ed4c1953249a142ae4d8ff65e Mon Sep 17 00:00:00 2001
From: Eric Wong <e@yhbt.net>
Date: Mon, 27 Sep 2010 14:16:55 -0700
Subject: [PATCH] README: update with support status

Well, the penguin rocks!
---
 README |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/README b/README
index 4dc2be9..5ba5739 100644
--- a/README
+++ b/README
@@ -10,11 +10,14 @@ from the IO class directly into BasicSocket with socket-specific system
 calls and flags.
 
 This library is only intended for Ruby 1.9 and will not build with other
-versions of Ruby.  This only supports operating systems with the
-non-POSIX MSG_DONTWAIT flag for send(2) and recv(2) syscalls.
-
-This library is considered EXPERIMENTAL.  If successful, we'll see about
-getting them integrated into the standard Ruby socket library.
+versions of Ruby.  This only supports operating systems with complete
+support of the non-POSIX MSG_DONTWAIT flag for send(2) and recv(2)
+syscalls on stream sockets.
+
+This library is fully-supported and stable on GNU/Linux 2.6+.  It is
+experimental and unsupported on other systems unless someone steps
+forward to support them.  Some operating systems have incomplete/broken
+support for the MSG_DONTWAIT flag on various types of stream sockets.
 
 == Features
 
-- 
Eric Wong
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