Re: [Fwd: Re: FW: matrix linking]

[Olivier Galibert <galibert at pobox dot com>]

On Fri, Nov 23, 2007 at 11:49:03AM +0300, george@georgeshagov.com wrote:
[Changing the _vptr or C equivalent dynamically]
> I would like the community would have considered the idea. I am ready to 
> answer all the questions you might have.

Changing the virtual function pointer dynamically using a serializing
instruction is I'm afraid just the tip of the iceberb.  Even
forgetting for a second that some architectures do not have
serializing instructions per se, there are some not-so-simple details
to take into account:

- the compiler can cache the vptr in a register, making your
  serialization less than serialized suddently

- changing a group of functions is usually not enough.  A component
  version change usually means its internal representation of the state
  changes.  Which, in turn, means you need to serialize the object
  (whatever the programming language) in the older version and
  unserialize it in the newer, while deferring calls into the object
  from any thread

- previous point means you also need to be able to know if any thread
  is "inside" the object in order to have it get out before you do a
  version change.  Which in objects that use a somee of message fifo
  for work dispatching may never happen in the first place

Dynamic vtpr binding is only the start of the solution.

  OG.