[Caml-list] perplexing marshaling exception

[Lex Stein <stein@eecs.harvard.edu>]

Hello, I'm having a curious and perplexing problem with unmarshaling
(Marshal module).

I have two executables that differ in that one is built from a C main
routine that calls into Caml closures via callback() and a second that is
built from code that makes these same calls from Caml directly. Both of
these programs call Caml routines that read/write records to Berkeley-DB
(BDB) via a homegrown Caml interface to the BDB C library. Here's a
diagram:

1: main program (C) | DB read/write (Caml) | BDB (C)
2: DB read/write (Caml) | BDB (C)

In 1, the main program does very little that's interesting. The only
values that it passes to its callbacks are copy_string()'ed pathnames
representing the location of the database. In 2, these same strings are
arguments to Caml source code calls to the same Caml routines that the C
code calls in case 1.

However, I get an error when I call from C (case 1) that I don't get in
case 2.

In case 1, in the DB read/write Caml code, when I try to unmarshal a
string retrieved from BDB, I get:

Fatal error: exception Failure("input_value: unknown custom block identifier")
(Program not linked with -g, cannot print stack backtrace)

In case 2, when I try to do this, I get no such error. (Also of interest
is the claim that the program was not linked with -g. This just isn't
true. However, this isn't my main concern).

Any idea what's going on here? Why unmarshal is failing when I have a C
main program?

Much appreciated!

Lex

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