Re: Continuations in custom port: "cannot invoke continuation from this context"

[Mark H Weaver]

Hi Caleb,

Earlier I wrote:
> Caleb Ristvedt <address@hidden> writes:
>
>> On Thu, Mar 28, 2019 at 12:58 PM Stefan Israelsson Tampe <
>> address@hidden> wrote:
>>
>>> I have not looked at this more carefully. But I suspect that the code is
>>> going to C land and then enters the scheme again
>>> via the hooks and then continuations won't work as expected.
>
>> Any idea why it would still be going to C land even with suspendable ports
>> installed? The manual says they're implemented in scheme for precisely this
>> reason.
>
> 'install-suspendable-ports!' replaces only a subset of the C port
> functions with Scheme implementations, namely the ones listed in
> 'port-bindings' in suspendable-ports.scm.
>
> The problem here is the custom port.  Custom ports are implemented in C,
> and are not reimplemented by suspendable-ports.scm.  When you perform
> I/O on the custom port, it enters C code in r6rs-ports.c which calls
> back into Scheme code to call your custom I/O handlers 'read!' and
> 'write!'.

Since writing this, I've written preliminary patches to add suspendable
I/O support for custom ports:

  https://lists.gnu.org/archive/html/guile-devel/2019-04/msg00019.html

I'd be curious to hear how it works in your use case.

      Mark