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Subject:	RE: OT: possible project/research project
Date:	Wed, 20 Mar 2002 18:14:01 +1100
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From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"Gary R. Van Sickle" <g DOT r DOT vansickle AT worldnet DOT att DOT net>, <cygwin AT cygwin DOT com>
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> -----Original Message-----
> From: Gary R. Van Sickle [mailto:g DOT r DOT vansickle AT worldnet DOT att DOT net] 
> Sent: Wednesday, March 20, 2002 1:52 PM

> 
> I don't see it that the source of the problem is the 
> implementation of fork/vfork; the way I see it the very 
> *concept* of forking makes little to no sense.  I've written 
> a lot of code, and not once have I thought to myself, "ok, 
> now what I want to do here is duplicate the current process 
> in almost exactly its current state."  Maybe it made more 
> sense back in the day, or maybe I'm missing something, but it 
> seems to me there's a lot more efficient ways to do 
> multithreading/multi"process"ing/IPC/etc (or better yet avoid 
> them altogether) these days.

Well, most high-performance systems use a combination of MT,MP and IPC.
Look at IIS for instance (not that I like MS :}). IIS uses in-process
filters to allow modularity and extensability, much like apache does -
now - with modules. (i.e. consider the php module vs the php cgi). In
such cases performance and scalability go up dramatically. However there
is a maintenance cost - it's harder to keep a system in good design the
more tightly coupled it is.

MT/MP and IPC will (IMO) allways have a place, because of the loose
coupling they allow. However COM & CORBA also allow loose coupling AND
in-process behaviour, so a happy can be found.

The issue at hand though, is twofold:
1) Minimise the changes needed to make a proxy for a program. I.e.
imagine if GCC and cc1plus.exe lived in-process. That would remove 2Mb
of disk IO for each compile. However the _only_ chance of getting such a
program proxied would be a minimalistic, non-intrusive approach, or
keeping a patched branch :[.
2) Make the context saving and restoring as low-overhead as possible.
(if this is > spawn() + wait, there is no point).

Rob

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