On Fri, 5 Jun 2020 13:17:09 +0200
Thomas Schwinge <tho...@codesourcery.com> wrote:
> Hi Julian!
>
> On 2019-12-17T21:03:47-0800, Julian Brown <jul...@codesourcery.com>
> wrote:
> > This part contains the libgomp runtime support for the
> > GOMP_MAP_ATTACH and GOMP_MAP_DETACH mapping kinds
>
> > --- a/libgomp/target.c
> > +++ b/libgomp/target.c
>
> > @@ -1203,6 +1211,32 @@ gomp_map_vars_internal (struct
> > gomp_device_descr *devicep,
>
> > + case GOMP_MAP_ATTACH:
> > + {
> > + cur_node.host_start = (uintptr_t) hostaddrs[i];
> > + cur_node.host_end = cur_node.host_start + sizeof
> > (void *);
> > + splay_tree_key n = splay_tree_lookup (mem_map,
> > &cur_node);
> > + if (n != NULL)
> > + {
> > + tgt->list[i].key = n;
> > + tgt->list[i].offset = cur_node.host_start -
> > n->host_start;
> > + tgt->list[i].length = n->host_end -
> > n->host_start;
> > + tgt->list[i].copy_from = false;
> > + tgt->list[i].always_copy_from = false;
> > + tgt->list[i].do_detach
> > + = (pragma_kind !=
> > GOMP_MAP_VARS_OPENACC_ENTER_DATA);
> > + n->refcount++;
> > + }
> > + else
> > + {
> > + gomp_mutex_unlock (&devicep->lock);
> > + gomp_fatal ("outer struct not mapped for
> > attach");
> > + }
> > + gomp_attach_pointer (devicep, aq, mem_map, n,
> > + (uintptr_t) hostaddrs[i],
> > sizes[i],
> > + cbufp);
> > + continue;
> > + }
>
> For the OpenACC runtime API 'acc_attach' etc. routines they don't, so
> what's the conceptual reason that for the corresponding OpenACC
> directive variants, 'GOMP_MAP_ATTACH' etc. here participate in
> reference counting ('n->refcount++' above)? I understand OpenACC
> 'attach'/'detach' clauses to be simple "executable clauses", which
> just update some values somewhere (say, like
> 'GOMP_MAP_ALWAYS_POINTER'), but they don't alter any mapping state,
> thus wouldn't appear to need reference counting?
IIUC, n->refcount is not directly the "structural reference count" as
seen at source level, but rather counts the number of target_var_descs
in the lists appended to each target_mem_desc -- and GOMP_MAP_ATTACH
have variable entries in those lists. That's not the case for the API
routines.
Julian
