libgomp nvptx plugin: rework initialisation and support the proposed load/unload hooks (was: Merge current set of OpenACC changes from gomp-4_0-branch)

[Ilya Verbin]

On Mon, Mar 30, 2015 at 18:42:02 +0200, Jakub Jelinek wrote:
> Shouldn't either this function, or gomp_offload_image_to_device lock
> also devicep->lock mutex and unlock at the end?
> Where exactly I guess depends on if the devicep->* hook calls should be
> guarded with the mutex or not.  If yes, it should be this function and
> gomp_init_device.
> 
> > +      if (devicep->type != target_type || !devicep->is_initialized)
> > +	continue;
> > +
> 
> Similarly.

Oops, there is a deadlock.  E.g. if gomp_map_vars locks devicep->lock and then
calls gomp_fatal, the destructors from .fini section are executed, so
gomp_mutex_lock in GOMP_offload_unregister will wait for devicep->lock.

  -- Ilya