[ANN] 1.9 users: socket_dontwait - MSG_DONTWAIT socket methods

Eric Wong normalperson at yhbt.net
Mon Aug 9 18:54:29 EDT 2010

Hi all,

I initially announced[1] this on the Rainbows! mailing list since
Rainbows! is more experimental in nature, but I've been running this for
a few days with real traffic (with Rainbows!) and it seems safe enough
for less crazy people to use :)

If you're using Ruby 1.9.1, then this library includes a fix for
errno getting zeroed and hitting rb_bug() during rb_sys_fail()
This is fixed in Ruby trunk r27401, but 1.9.1 doesn't have this.

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.

[1] - http://mid.gmane.org/20100803091847.GC3255@dcvr.yhbt.net

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
  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:


Unpack it, and run "ruby setup.rb"

== Development

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

  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

== 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 at rubyforge.org}[mailto:rainbows-talk at rubyforge.org].

Eric Wong

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