"Peter Dimov" <pdimov@mmltd.net> wrote in message news:009a01c6f39f$c72f3ff0$6507a8c0@pdimov2...
Hey Chris,
[...]
Here is a experimental prototype I created:
This doesn't contain any documentation, only source. You can't expect people to understand it without at least a brief reference that specifies what the various functions are supposed to do.
Yeah... Sorry. I plan on posting docs soon. [...]
Imagine that I add two member functions to shared_ptr:
shared_ptr<T> shared_ptr<T>::copy() const; // return *this void shared_ptr<T>::replace( shared_ptr<T> const & p ); // *this = p
that are synchronized with a mutex/spinlock/rwlock/rwspinlock and I declare that "strong" thread safety is offered only when everything goes through these two accessors and nothing else.
That should work...
Is this inferior to your proposed scheme?
Maybe... Currently, all of my pointer-ops are 100% lock-free. My reference count adjustments are 100% lock-free for everything except strong competing accesses (e.g., it only *takes a spinlock for strong competing accesses, **and when the count drops to zero). My counter objects can be swapped using normal word-based atomic operations (e.g., XCHG and CAS, no DWCAS required)... Also, I can use parts of my algorithm in the context of a signal handler. Can you use any part of shared_ptr<T> in a signal handler? I think the answer is going to be NO; however, I would love to be corrected if I am wrong... ;)
In what scenarios?
I think my scheme could possibly be more efficient because all of the pointer-ops are 100% lock-free, and most of the reference counts are 100% lock-free... Humm... I would have to see a sketch of the algorithm you have in mind Peter...
Can you implement the copy/replace interface in a "more lock-free way" using your scheme (you are allowed to add to sp_counted_base whatever members you need)?
Let me define some of the previous asterisks: *, **: The "hashed locking scheme can be completely replaced with one of my PDR schemes" I posted here: http://groups.google.com/group/comp.arch/browse_frm/thread/b2f751d5dad6c07b (DWCAS: no) or this one I posted here: http://groups.google.com/group/comp.programming.threads/msg/f443b38cf7bbca8a http://groups.google.com/group/comp.programming.threads/msg/a4a796e25a157ca1 (DWCAS: yes) This stuff is not in my prototype yet... I guess I should augment it with PDR. Once I do that, then I can implement copy/replace in a 100% lock-free way... Humm... Does any of this begin to address your questions Peter?