Re: [trans-mem] implement _ITM_dropReferences

[Richard Henderson <rth@redhat.com>]

On 06/23/2010 10:12 AM, Aldy Hernandez wrote:
> +void ITM_REGPARM
> +_ITM_dropReferences (const void *ptr, size_t len)
> +{
> +  gtm_transaction *tx = gtm_tx();
> +  tx->drop_references_local (ptr, len);
> +  tx->drop_references_allocations (ptr);
> +}

The primary thing missing here is dropping references inside
the actual transactional memory backend, i.e. gtm_dispatch.

> +/* Forget any references to PTR in the allocations tree.
> +
> +   ?? We ignore the chunk length.  Pray this doesn't wreck havoc.  */
> +
> +void
> +gtm_transaction::drop_references_allocations (const void *ptr)
> +{
> +  uintptr_t iptr = (uintptr_t) ptr;
> +
> +  gtm_alloc_action *a = this->alloc_actions.find(iptr);
> +  if (a == 0)
> +    {
> +      a = this->alloc_actions.insert(iptr);
> +      a->free_fn = NULL;
> +      a->allocated = false;
> +    }
> +
> +  a->ignore = true;
> +}

Why add the ignore field when you could simply alloc_actions.erase?

> @@ -65,13 +66,36 @@ gtm_transaction::rollback_local (void)
>        for (i = n; i-- > 0; )
>  	{
>  	  gtm_local_undo *u = local_undo[i];
> -	  memcpy (u->addr, u->saved, u->len);
> +	  if (!u->ignore)
> +	    memcpy (u->addr, u->saved, u->len);
>  	  free (u);
>  	}
>        this->n_local_undo = 0;
>      }
>  }
>  
> +/* Forget any references to PTR in the local log.  */
> +
> +void
> +gtm_transaction::drop_references_local (const void *ptr, size_t len)
> +{
> +  gtm_local_undo **local_undo = this->local_undo;
> +  size_t i, n = this->n_local_undo;
> +
> +  if (n > 0)
> +    {
> +      for (i = n; i > 0; i--)
> +	{
> +	  gtm_local_undo *u = local_undo[i];
> +	  /* ?? Do we need such granularity, or can we get away with
> +	     just comparing PTR and LEN. ??  */
> +	  if ((const char *)u->addr >= (const char *)ptr
> +	      && ((const char *)u->addr + u->len <= (const char *)ptr + len))
> +	    u->ignore = true;
> +	}
> +    }
> +}

Similarly, it seems easy enough to free the one element and test instead
in rollback_local for u == NULL.



r~