For the first example, I always thought the "runtime.KeepAlive" call is
essential before.
But after reading the explanations from Bryan C. Mills on Slack, I changed
my mind now.
Bryan C. Mills said: The GC tracks pointers through their original
allocations — the pointer scan does not care about lexical types, only
allocation types.
On Tuesday, April 21, 2020 at 8:11:49 PM UTC-4, Ian Lance Taylor wrote:
>
> On Tue, Apr 21, 2020 at 6:49 AM T L <tapi...@gmail.com <javascript:>>
> wrote:
> >
> > func String2ByteSlice(str string) (bs []byte) {
> > strHdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
> > sliceHdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
> >
> > // Is it possible that the str value is allocated on stack
> > // and the stack grows at this moment, so the address value
> > // stored in strHdr.Data will become obsoleted?
> >
> > sliceHdr.Data = strHdr.Data
> > sliceHdr.Len = strHdr.Len
> > sliceHdr.Cap = strHdr.Len
> >
> > runtime.KeepAlive(&str)
> >
> > return
> > }
>
> Since you are correctly using *reflect.StringHeader, it doesn't matter
> whether the stack is copied at that moment. You are pointing at the
> actual string value, so the pointer will be adjusted. As far as I can
> see, this is safe. (Of course, it's not safe if somebody modifies the
> contents of the returned []byte.)
>
> Ian
>
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