[boost] Re: how do I release shared_ptr ?

From: David Abrahams (dave_at_[hidden])
Date: 2004-01-08 07:48:14

"Joe Gottman" <jgottman_at_[hidden]> writes:

>> >     One major use for unique() is copy-on-write.  The code would look
>> > something like:
>> >
>> >     void write_to(shared_ptr<Foo> p, const Foo &newValue)
>> >     { // For simplicity, assume p.get() != 0
>> >         if (p.unique()) {
>> >             *p = newValue;
>> >         } else {
>> >             p.reset(new Foo(newValue));
>> >         }
>> >     }
>> >
>> > Under the current definition of unique(), this code is impossible to make
>> > thread-safe if weak_ptrs might exist.
>>
>> Would it work just as well if unique() returned weak_count?
>>
>
>    It would work better. If nobody is using weak_ptrs then weak_count equals
> 1 if and only if shared_count equals 1.  And if weak_ptrs are possible, then
> having unique() depend on weak_count guarantees that this code is
> thread-safe.

Are there any other use cases?  I think I was the one to argue for
"unique" in the first place, and COW was the only use I had in mind...

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com