[cfe-dev] TSan reports a race on vtable access (Clang/7)

[Oleg Smolsky via cfe-dev]

I've hit a funky TSan warning: "data race on vptr (ctor/dtor vs virtual 
call) in StartImpl()". I fail to see a race as the object is constructed 
in the main thread and then a worker thread is started:

struct Client : public ClientInterface {
   Client() {
     auto op = new Op{this};
     thread_ = std::thread([op] { op->StartImpl(); });
   }
   ...
};

void Op::StartImpl() {
   std::cout << "This is a race: " << owner_->VirtualFunction() << "\n";
}

struct TestClient : public Client {};

int main(int argc, char **argv) {
   TestClient().Wait();
   return 0;
}

The full report with a minimal/complete repro is here: 
https://github.com/google/sanitizers/issues/1063

What am I missing? Does TSan miss the fact that all data stores happen 
before the worker thread is started? Or is this about the vtable pointer 
which is adjusted during the object's construction in the main thread?

Thanks!
Oleg.