On Mon, Apr 22, 2013 at 4:26 AM, Andrea Galeazzi
I googled this question but, although there are many discussions about it, I didn't find a clear answer. Can I assume the following piece of code to be thread safe?
shared_ptr<T> p1(new XXX); //Main threadweak_ptr<T> wp(sp); //Main thread
//Then I run two threads: A and B p1.reset(); // thread A shared_ptr<T> p2 = wp.lock(); // thread B
In other words, is lock method atomic in respect to deference of the shared point?
Yes it is thread safe. To be clear (because I've seen this confusion before): shared_ptr<T> p1(new XXX); p1.reset(); // thread A p1.reset(); // thread B is NOT thread safe - used the same shared_ptr in 2 threads shared_ptr<T> p1(new XXX); shared_ptr<T> p2(p1); p1.reset(); // thread A p2.reset(); // thread B is thread safe - 2 shared_ptrs referencing the same object. Same with weak_ptr and various combinations. What you are doing is thread-safe. It is part of the docs, can be seen in the implementation (although it is hard to see), and tons of code would break if it wasn't. Tony