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Date: -- (:)
From: Charles 'Buck' Krasic <krasic@a...>
Subject: [Caml-list] interfacing C threads with OCaml

Hi,

I have a C program that contains a library implemented in OCaml
(native compilation).  The library glued to C using the techniques
described in Chapter 17 of the OCaml manual.

The overall program implements a pipeline of producer-consumer
functions, one of which is implemented in OCaml.  (The pipeline
implements an adaptive MPEG video player).  Each such function is an
infinite loop which alternates between produce and consume operations.
The OCaml one calls out to C primitives that do produce and consume
operations.  These primitives do marshalling between C datatypes and
OCaml.

It all works fine for a single pipeline, but I would like to support
concurrent pipelines where each pipeline is implemented by a separate
system thread (Linux pthreads).  

My OCaml pipeline function does a segmentation fault when I do this.
I have built the OCaml code using the -thread flag, and my link step
does -lthreadsnat.  I understand that the OCaml runtime is not
thread-safe, but I got the impression is that using -thread causes it
to use a single master lock, which is released when calling out to C
code; making it safe to mix threaded-C with OCaml.

Is this incorrect?

Are the marshalling macros in Chapter 17 (Store_field, etc.) safe wrt
the OCaml master lock?  

-- Buck
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