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From: Richard Stallman <rms@gnu.org>
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Subject: Re: Question about GC in C code.
Date: Mon, 11 Nov 2002 05:20:05 -0500
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    But I confess that I have no clue as how GC works in the C code.
    Will this approach work?  Will menu_bar_vector be safe from GC?

You have to modify the GC code in alloc.c to explicitly find these
C data structures in the menus and mark them the vectors by calling
mark_object.

    And when a struct menu_gtk_data is free:d, will menu_bar_vector
    then be a candidate for GC?

No, because the code you add to GC will not find it and mark it.

Is a detached menu a Lisp object?  If so, what data type is it?
Do we want a way to manipulate detached menus from Lisp?