It should work to just set the finalizer on the first byte of an
allocation. i.e.:
s := make([]byte, N)
runtime.SetFinalizer(&s[0], func(b *byte) { ... })
Note that the spec of runtime.SetFinalizer doesn't actually guarantee that
this will work. But I think in the current implementation it will.
> The argument obj must be a pointer to an object allocated by calling new,
by taking the address of a composite literal, or by taking the address of a
local variable.
The result of make isn't "an object created by calling new", but it it
close.
On Saturday, December 28, 2019 at 9:27:29 PM UTC-8, John wrote:
>
> Looking for a little insight on if it is possible to do something:
>
> Given this type:
>
> type Blah struct {
> Payload []byte
> }
>
> What I'm looking for is to kick off a finalizer when a slice and all other
> slices backed by the same array get GC'd.
>
> In lieu of that, whenver the pointer to the array backing a slice get's
> GC'd. I realize that in this case, the slice actually may stay around when
> the array is GC'd because an append creates a new array on the slice.
>
> I don't think the first is possible, as you can't call SetFinalizer() on
> non-pointer types. And I can't use any wrappers or pointers to []byte in
> lieu of []byte for my use case.
>
> I figure there is a way to use:
>
> hdr := (*reflect.SliceHeader)(unsafe.Pointer(&b.Payload))
>
> to set a finalizer on the underlying arrray.
>
> But I'm not sure exactly how to convert the hdr.Data into the specific
> array type pointer to use in SetFinalizer(). It may not be possible.
>
> To save some time on a few questions: I'm aware of the flaws of
> SetFinalizer(), just looking to see if this can actually be done.
>
> Thanks for any help.
>
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