From: Roger Pack <rogerpack2005@...>
Date: 2007-08-29T04:29:14+09:00
Subject: Re: Thread safety techniques for server applications?

Thanks for your comments.
Forgive me if I called modules/classes statically loaded.  What I meant 
was 'loaded before you start splitting to multiple threads' instead of 
static.

For example I have used xmlrpc before (which relies on REXML) and every 
so often (note the 'freak chance' aspect) it will throw the exception 
"REXML::Document not found" despite the fact that it indeed should be, 
and normally is.  I laid the blame on Ruby threads.  Where it belongs, I 
think is on...Ruby threads.  But having not actually ever fixed it, I 
can't say for sure.  I believe I've been able to recreate it reliably.



Joel VanderWerf wrote:
> Roger Pack wrote:
> ...
>> Also load up all your functions/everything 'single threaded' otherwise 
>> some of the functions will be 'assigned' to the wrong thread (ugh), then 
>> be unavailable (classes, modules, too).
>> I.e. dynamically declared functions are dangerous.
> 
> In ruby, everything is dynamically defined. The closest you can get to
> static definitions is to require all your lib files before starting
> threads. Even so, it's not really static. It might be safer in some
> cases because require-ing a file is not atomic.(*) That's a corner case,
> though.
> 
> I don't think it's possible for things to be unavailable because they
> were loaded in the wrong thread, though. Got an example?
> 
>> Note also that sometimes if you are reading from TCPSockets the sockets 
>> get confused and start reading from one another.
> 
> Really? I've never seen that, even with pretty heavy use of lots of
> threads and sockets.

Yeah I get it...sometimes a socket that is *only* used for sending will 
magically 'receive'...its own output! Wow!  And other weirdness.  Mostly 
on slower machines.  It is odd.  I noticed Zed Shaw said he'd run into 
the same thing (and was unable to track down the cause) in some thread 
or other here.  I honestly don't get it, either, but I think it's half 
the motivation to the creation of EventMachine.

Just my own $0.02
-Roger

> 
> ----
> 
> (*) An example:
> 
> [~/tmp] cat a.rb
> 
> t = Thread.new do
>    loop do
>      sleep 0.1
>      puts "a"
>    end
> end
> 
> sleep 0.5
> 
> require 'b'
> 
> [~/tmp] cat b.rb
> t = Thread.new do
>    loop do
>      sleep 0.1
>      puts "      b"
>    end
> end
> 
> sleep 1
> t.kill
> 
> [~/tmp] ruby a.rb
> a
> a
> a
> a
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a
>        b
> a

-- 
Posted via http://www.ruby-forum.com/.