c++11 Global initialization order and thread_local

Question

Hi when running the following using gcc 4.8.1 when using the thread_local keyword the assertion is hit. When removing the thread_local the assert is not hit. Does anyone know why this is? There is some undefined global ordering but I would expect buf_ to have a valid address before assigning ptr_. Just remove the keyword thread_local and it works for me.

Output:

$ ./ThreadLocal 
 Running Tester 
ThreadLocal: main.cpp:13: int main(): Assertion `buf == ptr' failed.
Aborted (core dumped)

Output when removing thread_local keyword
 Running Tester 

Test.hpp

 #include <iostream>
 #include <cassert>

template <typename std::size_t N>
struct Mem
{
    Mem() noexcept: ptr_(buf_)
    {}

    char * getBuf() { return buf_; }
    char * getPtr() { return ptr_; }

private:
    char buf_[N];
    char * ptr_;
};



template <typename std::size_t N>
struct Tester
{
    Tester()
    {
        std::cout << " Running Tester " << std::endl;
    }

    char * getPtr() { return _mem.getPtr(); }
    char * getBuf() { return _mem.getBuf(); }

private:
    static thread_local Mem<N> _mem;
}; 

main.cpp

#include <iostream>
#include "Test.hpp"

template <typename std::size_t N>
thread_local Mem<N> Tester<N>::_mem;

int main()
{
    Tester<500> t;
    char * ptr  = t.getPtr();
    char * buf = t.getBuf();

    assert( buf == ptr );
}

Answer 1

It looks like a bug in GCC. Apparently Tester::_mem is not being initialized at all. GCC 4.9.0 does the same, but clang 3.5.0 works fine

Making _mem not dependent on template parameter makes GCC crash.

Finally, making Tester a non-template class makes GCC work at last.

Update: These seem to be known bugs in GCC.