Re: Continuing my foray into the TR1: tr1::shared_ptr<>

"Emmanuel Deloget" <logout@free.fr> wrote in message
news:1172835752.748131.203690@8g2000cwh.googlegroups.com...


Here is a fairly efficient way to implement shared_ptr:

http://appcore.home.comcast.net/vzoom/refcount/
(I expose a different interface than shared_ptr, however, it would be
trivial to make my algorithm expose it as well.)

Also, when you use something like the algorithm I created you get the added
benefit of strong thread safety. Currently, shared_ptr cannot handle strong
competing access from multiple threads... In other words, the following
scenario is a no go with current shared_ptr algorithm, and perfectly legal
with my prototype code:

// pseudo-code

static shared_ptr<foo> g_foo = new foo;

reader_threads(...) {
  for(;;) {
    {
      shared_ptr<foo> l_foo = g_foo;
      if (l_foo) {
        l_foo->do_something();
      }
    }
    // do something else
    // ect, ect...
  }
}

writer_thread(...) {
  for(;;) {
    {
      shared_ptr<foo> l_foo = g_foo.xchg(new foo);
      if (l_foo) {
        l_foo->do_something();
      }
    }

    // do something else
    // ect, ect...
  }
}

Does anybody think that shared_ptr should be able to handle a scenario like
the above? If you think so, my prototype implementation should help inspire
some other possible designs...