Double Free error with AddressSanitizer GCC 4.8

Question

Consider the following toy program(prog.cpp):

class A {
public:
    vector<int> vec;
    A() noexcept {}
    A(vector<int> s) : vec(s) {}
};

class B {

private:
    vector<atomic<A>> a_table;

public:
    B(int capacity) : a_table(capacity) {}

    void update(int index) {
        A newValue(vector<int>(10,1));
        a_table[index].store(newValue);
    }
};


int main(int argc, char** argv) 
{
B b(5);
b.update(2);
return 0;
}

This when compiled normally (g++ prog.cpp -latomic), works fine. But when compiled as g++ -fsanitize=address -fno-omit-frame-pointer prog.cpp -latomic produces Double Free error when executed. A program based on similar lines as above has to be used in a multi-threaded application, where even the normal compilation is producing Double Free error. I read up Rule of Three/Five, which is generally referred to in case of Double Free, and various other documentations but nothing worked.

Also, removing noexcept specifier from the class A's default constructor produces this strange error, which also I would like to know about.

error: function ‘std::atomic<_Tp>::atomic() [with _Tp = A]’ defaulted on its first declaration with an exception-specification that differs from the implicit declaration ‘std::atomic<A>::atomic()’
   atomic() noexcept = default;
   ^

Answer 1

std::atomic requires a trivially copyable type, which your A is not, because its member of type vector<int> (e.g.) is not trivially copy constructible.

GCC only detects a violation of that requirement since version 5.0.

The fact that older gcc versions compile the code does not mean that it is valid.