At Fri, 1 Nov 2019 10:34:50 -0700 (PDT), Thomas Dickerson wrote:
> The documentation says:
> "The 3m collector needs to know the address of every local or temporary
> pointer within a function call at any point when a collection can be
> triggered."
>
> A couple questions:
> - Is this "every pointer which might be passed to a Racket function, or
> contain the result of a Racket function"? Or is it truly *every pointer*?
Only pointers to GCable memory --- which tends to be the things passed
to a Racket function, but more generally corresponds to things that
come from Racket .
> - Do I need to register the data pointer passed to
> `scheme_main_stack_setup`, even though this is above the GC's stack base?
No. As you say, that's before the GC is ready.
> - In an instance method, does `this` need to be registered? What about
> reference types?
A `this` pointer does not point to GCable memory, unless you do well
out of your way to allocate an object with Racket's allocator.
The value of a variable with a reference type would normally correspond
to an address on the C stack, so it would not need to be registered.
At Fri, 1 Nov 2019 11:41:18 -0700 (PDT), Thomas Dickerson wrote:
> The output of `raco ctool --c-mods` has the form:
>
> #ifdef MZ_XFORM
> > XFORM_START_SKIP;
> > #endif
> > static void declare_modules(Scheme_Env *env) {
> > static unsigned char data[] = { /* bytes go here */ };
> > scheme_register_embedded_load(NUM_BYTES, (const char *)data);
> > scheme_embedded_load(NUM_BYTES, (const char *)data, 1);
> > }
> > #ifdef MZ_XFORM
> > XFORM_END_SKIP;
> > #endif
> >
>
> As I understand it, this means there's no reason to pass it through `raco
> ctool --xform`, which presumably means we don't need need to register `env`
> or `data`, but we are seeing `scheme_embedded_load` in the stack trace of
> some Racket routines that triggered a watchpoint on memory that it
> shouldn't be touching, so I just wanted to double check that's indicative
> of a problem upstream.
The `data` pointer is ok because it refers to statically allocated
memory, which is not managed by the GC. The `env` pointer isn't
registered because it isn't used, so it's ok if `env` gets out of date.
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