From: Gail Rahn (gail_at_screaminggeek.com)
Date: Mon Jan 12 2004 - 18:14:19 PST
The "Programming Sematics for Multiprogrammed Computations" paper by Dennis
and Van Horn describes meta-instructions used in programs that are run in
multiprogramming environments. The paper describes a low-level grammar,
between assembly and algebraic languages, that handles privilege-granting to
"computational objects" (processes, etc.). The meta-instructions handle
granting and revoking read/write/execute privileges for data blocks, process
creation and termination (fork, quit and join), privilege inheritance,
mutual exclusion, debugging. The authors describe a toolbox of objects that
are useful for programmers in parallel/multiprogramming situations. The
authors also create interesting supporting notes in the paper, including an
early aside about the parallel program design features.
The authors propose a C-List as the unit of privilege for a particular
segment. A c-list is list of segments adn the privileges assigned to it,
relative to the process owning the C-list. The C-list is created by the
supervisor program at runtime.
The authors indicate that the described system is necessarily incomplete,
because the expectations of operating system support of running processes is
evolving and more features will likely be considered standard in the future.
I especially enjoyed the paper's discussion of protected entry points. It
sounded ot me like an early discussion of shared libraries or DLLs, where
only certain entry points are allowed into a separate blob of executable
code.
The discussion of directories and naming was confusing to me. I found it an
incomplete evaluation of the importance of string names for files. Also, the
idea that "people are used to thinking in terms of invariant names" is
clearly wrong and outdated. If I name a file "last month's expenses" then in
the next month, I am expecting to rename it.
Also, I didn't find the idea that a file's privileges are somehow based on
its file path, whether the file exists in a principal's root directory, to
be particularly relevant in the modern age.
-- Gail.
grahn_at_cs.washington.edu
-------------
Gail Rahn
gail_at_screaminggeek.com
206.719.5563
Screaming Geek Software
www.screaminggeek.com
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