TSAN race on vptr for object published via CAS

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <pthread.h>

//------------------------------------------------------------------------------

class IFactory
{
public:
    virtual ~IFactory() { /* */ }
    virtual void bar() { printf("Default bar\n"); };
private:
};

class Factory : public IFactory
{
public:
    virtual void bar() { printf("Factory::bar()\n"); }
private:
};

//------------------------------------------------------------------------------

IFactory * get_factory_instance()
{
    static IFactory * s_factory_instance = NULL;
    if (s_factory_instance == NULL) {
        IFactory * factory = new Factory();
        if (__sync_val_compare_and_swap(&s_factory_instance, NULL, factory) != NULL) {
            delete factory;
        }
    }
    return s_factory_instance;
}

//------------------------------------------------------------------------------

void * thread(void * x)
{
    IFactory * impl_factory = get_factory_instance();
    impl_factory->bar();
    return NULL;
}

//------------------------------------------------------------------------------

int main()
{
  pthread_t t[2];
  pthread_create(&t[0], NULL, thread, NULL);
  pthread_create(&t[1], NULL, thread, NULL);
  pthread_join(t[0], NULL);
  pthread_join(t[1], NULL);

  return 0;
}

/*
Factory::bar()
==================
WARNING: ThreadSanitizer: data race on vptr (ctor/dtor vs virtual call) (pid=2452)
  Read of size 8 at 0x7d040000eff0 by thread T2:
    #0 thread(void*) /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:43:5 (test_vptr_con+0x00000009eb71)

  Previous write of size 8 at 0x7d040000eff0 by thread T1:
    #0 operator new(unsigned long) <null>:0 (test_vptr_con+0x0000000273fd)
    #1 get_factory_instance() /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:30:9 (test_vptr_con+0x00000009ea20)
    #2 thread(void*) /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:42:31 (test_vptr_con+0x00000009eb40)

  Location is heap block of size 8 at 0x7d040000eff0 allocated by thread T1:
    #0 operator new(unsigned long) <null>:0 (test_vptr_con+0x0000000273fd)
    #1 get_factory_instance() /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:30:9 (test_vptr_con+0x00000009ea20)
    #2 thread(void*) /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:42:31 (test_vptr_con+0x00000009eb40)

  Thread T2 (tid=2464, running) created by main thread at:
    #0 pthread_create <null>:0 (test_vptr_con+0x00000002a6c1)
    #1 main /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:53:3 (test_vptr_con+0x00000009ec13)

  Thread T1 (tid=2463, finished) created by main thread at:
    #0 pthread_create <null>:0 (test_vptr_con+0x00000002a6c1)
    #1 main /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:52:3 (test_vptr_con+0x00000009ebe9)

SUMMARY: ThreadSanitizer: data race on vptr (ctor/dtor vs virtual call) /home/eiva/git/tb/src/servers/test_vptr_con/src/t.cpp:43 thread(void*)
==================
Factory::bar()
ThreadSanitizer: reported 1 warnings
*/