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Yes, Allen gives an excellent summary of Actors, and I agree with
Barry that it's worthwhile to explore the commonalities of the Actor
model and CSP. I would recommend, in particular, Gul Agha's 1985
dissertation, "ACTORS: A Model of Concurrent Computation in
Distributed System." Here is a link to the PS or PDF file, for your
reading pleasure: :-)
One caution, which may not be immediately apparent as you read, is
when Agha references CSP, it is Hoare 78 CSP, not the 1985 text
version, which was published the same year as Agha's monograph. While
I am not familiar with the dialect of Actors that Claude described in
his reply, I would add the following to characterize one of the
differences between Actors and CSP: CSP processes compose
deterministically by default, but due to the mailbox infrastructure
by which actors communicate, actors compose nondeterministically:
message delivery is guaranteed, but order of delivery is not. In some
sense, this is the actor equivalent of ALTing.
If misery loves company, the CSP and Actors communities share much in
common: they are both largely misunderstood and under-appreciated
general models of concurrency. They both have strong semantic
foundations, and thus are reduced to sound-bites when described to,
and dismissed by, the under-informed masses.
CSP and the Actors model share much common ground. My sense is that
if an Actors implementation suffers from some of the same issues as
threading models, it is likely an implementation issue, not the
Actors model itself.
Marc L. Smith
Assistant Professor, Computer Science
Vassar College, Box 399
Poughkeepsie, NY 12604
On Feb 22, 2007, at 2:51 PM, Barry Cook wrote:
Allan gives a very nice summary of the differences between the
Actor model and CSP - but there are also very many things in common
- or at least common desires. I found the article in http://
en.wikipedia.org/wiki/Actor_model VERY thought provoking.
Maybe we are less out-on-a-limb than we think (?)
I need to follow-up some of the leads from this article, and other
places. The Actor model has not been much mentioned in WoTUG (CPA)
[as far as I can remember] - is there a good reason for this or
should we be looking at it more seriously?
Dr Barry M. Cook, BSc, PhD, CEng, MBCS, CITP, MIEEE
----- Original Message ----- From: "Allan McInnes"
Sent: Thursday, February 22, 2007 3:09 AM
It's probably worth noting that Will Clinger (mentioned in the
Brendan's blog) did a bunch of work on the Actor model of
concurrency. So it's
concurrency. The Actor model shares a lot of ideas with CSP, but
also has a few
key differences, e.g. asynchronous rather than rendezvous
message delivery based on the identity of the receiver rather than
(Erlang, for those familiar with it, uses a message-passing
approach along the
lines of the Actor model).
Of course, it's pretty straightforward to build a CSP-like channel-
rendezvous messaging system on top of an Actor-style system, so
Tom's idea of a
instead of the CSP one. Either approach would be a vast
threads with shared state.
Quoting Tom Locke <tom@xxxxxxxxxxxxx>:
I find the following to be of extreme importance to us CSP lovers:
A requirement for JS3 (along with hygienic macros) is to do
something along these more implicit lines of concurrency support. In
all the fast yet maintainable MT systems I've built or worked on,
key idea (which Will Clinger stated clearly to me over lunch last
fall) is to separate the mutable unshared data from the immutable
shared data. Do that well, with language and VM support, and threads
become what they should be: not an abstraction violator from hell,
but a scaling device that can be composed with existing
So here's a promise about threads ... JS3 will be ready for the
multicore desktop workload.
become The Next Big Language. Static typing is being added, as well
as other "in the large" features. Performance is becoming
with Java. I think it's already the most widely known language...
Some of you heavy-hitters really need to start up a dialogue with
Of course the future is always murky, but there's a pretty real
possibility that this is *the* opportunity to take the CSP ideas we
love mainstream. An opportunity such that has never existed and may
At *least* it might be possible to steer things such that the
primitives can support fine-grained, high performance CSP via a
Peter - remember your CSP workshops at Sun where you convinced
everyone except Gosling? Time for a re-run at the Mozilla
These open-source types are much cuddlier than corporate lackeys
Time to act!
Allan McInnes <amcinnes@xxxxxxxxxx>
Dept. of Electrical and Computer Engineering
Utah State University