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Subject: Re: [Boost-users] Thread Safety of shared_ptr
From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2011-05-02 10:28:55

On Mon, May 2, 2011 at 4:23 PM, Ovanes Markarian <om_boost_at_[hidden]>wrote:

> On Mon, May 2, 2011 at 3:01 PM, Frank Mori Hess <frank.hess_at_[hidden]>wrote:
>> Hash: SHA1
>> On Monday, May 02, 2011, Peter Dimov wrote:
>> > > // thread B
>> > > // p2 goes out of scope: undefined, the destructor is considered a
>> > >
>> > > "write access"
>> >
>> > This example just says that you can't make a copy of a destroyed
>> > shared_ptr, or one that is in the process of being destroyed. In
>> > principle, it has nothing to do with reference counts. Doing something
>> > with a destroyed object of any type is undefined behavior in C++.
>> It looks like the example isn't quite right though, as p2 was declared in
>> thread A so it can't go out of scope in thread B.
> It still can happen if p2 is a weak_ptr in thread "A" and the corresponding
> shared_ptr goes out of scope in thread "B".
> Best Regards,
> Ovanes

Actually, I am not sure with this statement. Destructor is only called if
shared count reaches zero. I don't think that this can happen, that a dtor
is called in one thread and the other thread is still able to increment the
shared count even from the weak_ptr. I remember reading weak_ptr's source
and saw that it is also protected again such a case.


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