From: Bill Kelly <billk@...>
Date: 2005-12-24T07:16:53+09:00
Subject: Re: kernel#select and threads

From: "Jon Smirl" <jonsmirl@gmail.com>
> Does calling kernel#select stop all ruby threads while it is waiting
> or does the interpreter run the select on a different kernel thread?
> By running the select on another kernel thread other ruby threads
> could run while this call is blocked.

Ruby multiplexes it behind the scenes, using just one native thread.
If one ruby thread does a select and would block, ruby will switch
to a different ruby thread.  If all ruby threads wanted to select
and block, ruby's scheduler would really do a blocking select.  

The catch is that some system calls, like write() or send() may block
the whole native process thread, causing all of ruby's green threads
to block.  In practice you can usually avoid this on Unix systems
with:

 sock.fcntl(Fcntl::F_SETFL, sock.fcntl(Fcntl::F_GETFL) | Fcntl::O_NONBLOCK)

On Unix systems, I think the NONBLOCK setting will work on file and
pipe I/O as well as sockets.

On Windows, i don't think there's any way to do non-blocking I/O
from ruby, yet.


Regards,

Bill