[v3] extern/fixed-memory/archive allocator

[Gabriel Dos Reis]

Benjamin Kosnik <bkoz@redhat.com> writes:

| I'm planning on using this in place of the current strategy for
| allocating global objects. Seems to work well in preliminary tests, but
| I post this for more comments.
| 
| This is just a way of taking existing storage and fitting it in to the
| std::allocator model so that STL, string, etc can use it. It can be thought of 
| 
| http://gcc.gnu.org/ml/libstdc++/2003-01/msg00103.html
| 
| crossed with src/global*.cc
| 
| Actually I'd like to experiment with pre-allocating space for pools in
| mt_alloc with this. But, that's a later patch.


I really like the general idea.  And I'd like to see our basic_string
use that technique too.  However I think we would need first to fix the
front-end so that this works properly

+       typedef char layout_type[sizeof(_Tp)] 
+       __attribute__ ((aligned(__alignof__(_Tp))));

Also, I'm wondering whether it should not be

   
  typedef char storage_type[sizeof(_Tp)];
  storage_type _M_instance  __attribute__((__aligned__(__alignof(_Tp))));

(as I remember -- maybe that is fixed now -- attributes on array
typedefs used to be silently stripped)


We might want to abstract that into a standalone class, as it
basically implement the aligned_storage functionality in TR1.


-- Gaby