From: Robbert VanRenesse <rvr@cs.cornell.edu>
Date: Tue, 24 Oct 1995 13:47:59 -0400
Message-Id: <199510241747.NAA00861@snotra.cs.cornell.edu>
To: caml-list@pauillac.inria.fr
Subject: question of a layman
I have built a complex system in C, and now I'm thinking of options to
re-implement it in CAML.
In short: we at Cornell University are building a communication system
called Horus. Horus is a framework that allows the composition of
microprotocols into more complex protocols. Examples of microprotocols
are sliding window protocols, fragmentation/reassembly protocols, ordering
protocols, and membership protocols. Each micro-protocol is fairly simple,
and has the *same* top and bottom-level interfaces. In particular, these
interfaces contain send and deliver. For example, the sliding window
micro-protocol's send operation adds a sequence number to a message and
invokes the send operation of the micro-protocol below it.
Basically, we can build complex protocols by stacking instances of
micro-protocols on top of each other. Also, we want to be able to run
multiple stacks at a time (if only to maintain connections to different
peers). Each instance of a micro-protocol maintains some state.
How would you implement something like this in CAML? We did an initial
version, which follows the C version and uses mutable records to maintain
the protocol state. However, even though it works, this does not appear
to me as the most natural way of doing it.
I guess the most natural way of implementing a micro-protocol in CAML is
as a stream to stream function. A stream is then a stream of send and
deliver (and other) events. You can then build a stack by composing these
functions.
However, two things are still unclear to me:
1) how do you run multiple of these functions at a time in the same
address space?
2) how do you link it into an existing application written in C. That is,
when the C application invokes send(), how do I plug this event into
the event stream of the function? And, perhaps the same question, how
do I make sure that the function maintains its state?
I have a multi-threading system, and I can probably run the CAML interpreter
in thread separate from the application that is written in C, which may be
part of a solution.
I guess the most natural solution would be to run each composition of
stream functions in its own thread, but I don't know how hard this is
to support, or even if this is desirable. If necessary, I could run
each one in its own address space, but that would be expensive.
I would appreciate any answers/comments.
Robbert