Re: Marshaling of custom blocks and threads

[Gerd Stolpmann <gerd@gerd-stolpmann.de>]

On Tue, 28 Nov 2000, Ken Wakita wrote:
>I think the Marshal module is thread unsafe because it uses a shared
>buffer to produce the external image of the ML objects.

In 2.04, this was definitely true
(see http://caml.inria.fr/bin/caml-bugs/fixed?id=24;page=1;user=guest
and http://caml.inria.fr/bin/caml-bugs/fixed?id=25page=1;user=guest).
However, the bug was still subtle; the shared buffers were relatively 
well protected by the so-called "master lock". Until now, I thought
that 3.00 fixed the bug finally; i.e. the master lock really locked
the shared buffer. (I checked the code.)

Jocelyn Serot reports that Marshal is not thread-safe for custom blocks.
These did not exist in 2.04, so I suppose that only the new parts of the
marshalling system do not work properly enough. However, multi-threading
programming is error-prone, so it would be helpful to have a small program that
demonstrates the bug (normally it is sufficient to repeat the errorneous piece
of code often enough (e.g. 10000 times) to reproduce the incorrect behaviour).

Gerd
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