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From: deven@rpi.edu (Deven Corzine)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MEMF_LOCKED
Message-ID: <DEVEN.89Jun2192814@daniel.rpi.edu>
Date: 2 Jun 89 23:28:14 GMT
References: <8906010339.AA12100@jade.berkeley.edu>
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Organization: RPI Public Access Workstation Lab, Troy NY
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In-reply-to: 451061@upttawa.BITNET's message of 1 Jun 89 01:51:43 GMT

In article <8906010339.AA12100@jade.berkeley.edu> 451061@upttawa.BITNET (Valentin Pepeleat) writes:

> Deven Corzine <deven@rpi.edu> writes in
> Message-ID: <DEVEN.89May30030703@daniel.rpi.edu>

> > Ah, but you see...  it basically operates on the assumption that
> > there is not only a single address space, but no memory protection
> > as well...

> Ridiculous! Memory protection merely prevents tasks from overwriting
> each other. It does not prevent them from reading each other's
> address space. And by declaring memory to be public, writing in each
> other's space is allowed too.  Read protected memory is useful only
> in multi-user systems.

In some contexts, memory protection DOES mean read-protection as well
as write.  It's implementation-defined, really.  Regardless, the
message passing system _depends_ on absence of memory protection.
Read AND write.  (consider ReplyMsg)  And don't count on MEMF_PUBLIC
ever being meaningful...

> If you have separate address spaces, then you can not read and write
> each other's address space. You share data only by sending messages.
> That is very icky, very Unix-like.

That is very clean.  Reading and writing others' address spaces is
"icky".  Shared memory is often a clumsy method of IPC.  Besides,
shared memory COULD very well be implemented, ON REQUEST, with read-
and write-procted, separately addressed, paged memory.  Stop mixing
the issues.

Deven
--
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