From: Francis Cianfrocca <garbagecat10@...>
Date: 2007-01-30T00:56:40+09:00
Subject: Re: Benefits of Multi-Threading?

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On 1/28/07, khaines@enigo.com <khaines@enigo.com> wrote:
>
> On Mon, 29 Jan 2007, Justin Collins wrote:
>
> > There are two main reasons for using multi-threaded applications, even
> on a
> > single processor:
> >
> > The first is performance. It's faster to switch between threads than it
> is
> > between processes, and it's (typically) even faster to switch between
> > user-level threads like Ruby has. Also, any asynchrony in your program
> (like
>
> That's a bit of a red herring, though.  With Ruby's green threads, every
> active (i.e. not sleeping) thread that is added to a single process
> reduces the overall throughput of all of the threads, collectively, by a
> noticable amount.  While two separate processes on a single processor may
> have less throughput than two threads in a single ruby process, those two
> threads will have less throughput than a single thread.  So, a single
> thread solution will typically be more performant than multi-thread
> solution under Ruby's current threading model.



 I'll second that and add this: Ruby works around the classic green-thread
problem (blocking the whole process when a single thread blocks in a system
call) by polling a medium-frequency timer interrupt. Total performance in a
Ruby program with two threads isn't just lower than in single-threaded
program- it's a LOT lower.

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