[Caml-list] faq? gc'd channels & finalize?

[Caml-list] faq? gc'd channels & finalize?

[Chris Hecker]

This must be an FAQ, but I can't find anything about it in the FAQ, the docs, and only a few messages on the caml list early last year...

File handles (channels) are not closed on garbage collection, right (my tests indicate they're not)?  Why is this (just because no guarantees can be made on when objects will be finalized)?  The docs warn against using finalization routines, so it seems like manually doing it (or using a wrapper function, which then has to catch and reraise exceptions) is the only way.

Chris

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Re: [Caml-list] faq? gc'd channels & finalize?

[Xavier Leroy]

> File handles (channels) are not closed on garbage collection, right
> (my tests indicate they're not)?

This is correct.

> Why is this (just because no
> guarantees can be made on when objects will be finalized)?

That's one reason.  Another reason is that when you have a low-level
file descriptor (Unix.file_descr) and build a channel around it
(Unix.{in,out}_channel_of_descr), it is often the case that you don't
want the file descriptor to be closed when the channel becomes garbage
collected -- your code may still be using the file descriptor.

> The docs
> warn against using finalization routines, so it seems like manually
> doing it (or using a wrapper function, which then has to catch and
> reraise exceptions) is the only way.

I'm not sure which part of the doc you're referring to, but with the
new per-object finalization facility of OCaml 3, I think it is safe
to do
        Gc.finalise close_out my_out_channel
or
        Gc.finalise close_in my_in_channel

for the channels you'd like to see finalized.

- Xavier Leroy
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