From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id LAA30361; Mon, 19 Mar 2001 11:42:18 +0100 (MET) X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id LAA30624 for ; Mon, 19 Mar 2001 11:42:17 +0100 (MET) Received: from pauillac.inria.fr (pauillac.inria.fr [128.93.11.35]) by concorde.inria.fr (8.11.1/8.10.0) with ESMTP id f2JAgB909072; Mon, 19 Mar 2001 11:42:11 +0100 (MET) Received: (from xleroy@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id LAA30551; Mon, 19 Mar 2001 11:42:10 +0100 (MET) Date: Mon, 19 Mar 2001 11:42:10 +0100 From: Xavier Leroy To: eijiro_sumii@anet.ne.jp Cc: caml-list@inria.fr, sumii@venus.is.s.u-tokyo.ac.jp Subject: Re: [Caml-list] questions about marshalling Message-ID: <20010319114210.A30440@pauillac.inria.fr> References: <20010317230450C.sumii@yl.is.s.u-tokyo.ac.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <20010317230450C.sumii@yl.is.s.u-tokyo.ac.jp>; from eijiro_sumii@anet.ne.jp on Sat, Mar 17, 2001 at 11:04:50PM +0900 Sender: owner-caml-list@pauillac.inria.fr Precedence: bulk > (1) Is it safe to marshal values of a statically polymorphic type, like > > let f x = Marshal.to_channel outchan (x, x) [Marshal.Closures] > > for example, provided that the marshaled values will be unmarshaled as > values of the right types at runtime? Yes, it is safe. > (2) Is it safe to *un*marshal a value at a statically polymorphic type > and use it later at a statically monomorphic type, like > > let g x = fst x > let y : int = g (Marshal.from_channel inchan) > > for example, provided that the value has the right type at runtime? Again, provided the run-time type is correct, this is safe. > My guess is that both of these are safe, even though the document says > > The programmer should explicitly give the expected type of the > returned value, using the following syntax: `(Marshal.from_channel > chan : type)'. > > because the (un)marshaling function itself works on the basis of the > runtime tag rather than the static type of a value -- a catastrophe > may be caused *later* when the value is actually used at a wrong type. > Am I correct? Yes. The documentation perhaps needs to be worded differently. Constraining immediately the return value of Marshal.from_channel to the correct type is a good way to reduce the probability of programming errors induced by the fake polymorphic type of this function, but it is not an absolute requirement. > (3) Yet another question: in a program using marhsaling (via ocamlmpi, > actually), I get the following error: > > Fatal error: uncaught exception Failure("input_value: ill-formed message") > > What does this mean? I am quite sure that all the hosts are > running the same binary, and I am using only ocamlmpi for > communication. Does this necessarily mean that I gave a wrong > type for the unmarshaled value (in Mpi.receive, to be specific), > or are there other possibilities? No, this is not a "wrong type" error. It means that the binary data given to the unmarshaler is not valid, e.g. was not produced by the marshaller, or got corrupted, or truncated, or padded, or whatever change, during transmission. This might indicate a bug in ocamlmpi, or a problem in the underlying MPI implementation or transport layers. If you have a test program that reproduces the error, you can send it to me and I'll have a look. Hope this helps, - Xavier Leroy ------------------- To unsubscribe, mail caml-list-request@inria.fr. Archives: http://caml.inria.fr