Re: [boost] Is shared_ptr really thread safe ?

From: Larry Evans (jcampbell3_at_[hidden])
Date: 2002-05-04 10:06:53

Larry Evans wrote:
[snip]

>
> I hope that's correct.  Now, if this is true, then I think things could
> be speeded up by using "weighted reference count" or WRC's.
> With WRC's, the only time a lock is needed is during deletion of
> a smart_ptr.

The last sentence overstated the case.  Whenever an "arc" is
deleted is when a lock is needed.  In other words, if
smart_weighted_ptr::get is non-null,
then when it changes to another referent, the previous referent's
weighted reference count must be updated; hence, a lock is required.
However, the new referent's reference count is NOT updated, only
the smart_weighted_ptrs' (the source and target) weighted reference
counts are updated.  Hence, less than 1/2 of the locks are required.  The
number of locks correspond to the number of reference count decrements
in the current smart_ptr.

At least I think that's right.  Maybe Jones or Lins could correct me.