2012/4/18 Yuanlong Shao

Hi all,

If I do the following

---------------------------------------------------------------------------------------------------------- shared_ptr<int> pA( new int(1) ); shared_ptr<int> pB( new int(2) ); shared_ptr<int> pNew( new int(3) );

// thread A pA = pB;

// thread B pB = pNew;

----------------------------------------------------------------------------------------------------------

I know that whether pA will be int(2) or int(3) after execution is undefined, but if I do want to do this no matter what value of pA I get, will this cause atomicity problem? I mean, thread A increases counter for int(2), but thread B decrease it, is this thread safe?

No, it's not thread safe. It's not allowed to read a shared_ptr while another thread simultaneously modifies the same object. See http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/shared_ptr.htm#ThreadSaf... . Roman Perepelitsa.