Validate string type when constructing IO::Buffer for string mapping.

[ioquatix]

You need to check it's actually a String before calling this.
And also you need to pin it to avoid it moving when GC.compact/autocompact is used.

[ioquatix]

@tenderlove how do you pin an object, in this case source so it can be moved? Do we need to do something special?

[eregon]

I found ruby/fiddle#44 but I'm not sure how to apply it for this case, cc @tenderlove

[ioquatix]

We already have:

void
rb_io_buffer_type_mark(void *_data)
{
    struct rb_io_buffer *data = _data;
    rb_gc_mark(data->source);
}

Is it enough? How do we handle moving?

[tenderlove]

@ioquatix rb_gc_mark will already pin it, so we don't need to worry.

[ioquatix]

@tenderlove thank you so much, it's really helpful to have your advice.