In which thread is the terminate handler called?

Question

In which thread is called the terminate handler:

1. when an exception is thrown inside a noexcept function?

2. when the user call std::terminate()?

3. at start up or destruction of thread?

Is it defined in the standard, will I have access to thread_local objects?

Answer 1

This answer sum up answers given in comments and an answer now deleted:

• It is not specified in the standard (DeiDei, I have checked too in N4618)

• Nevertheless, for technical reasons it is unlikely that the handler is called in an other thread that the one who caused the call to std::terminate (Galik,Hans Passant)

• it has been verified on online compiler (Rinat Veliakhmedov), the terminate handler is called in the thread that causes terminate to be called.

You can test it yourself with this code from a deleted answer:

#include <string>
#include <exception>
#include <iostream>
#include <thread>
#include <mutex>

std::mutex mutex;
const auto& id = std::this_thread::get_id;
const auto print = [](std::string t){
    std::lock_guard<std::mutex> lock(mutex);
    std::cout << id() << " " << t << std::endl;
};

void my_terminate_handler(){
    print("terminate");
    std::abort();
}

void throwNoThrow() noexcept { throw std::exception(); }
void terminator()            { std::terminate();       }

int main() {
    std::set_terminate(my_terminate_handler);
    print("main");    
#ifdef  CASE1
    auto x1 = std::thread(throwNoThrow);
#elif CASE2
    auto x1 = std::thread(terminator);
#elif CASE3    
    auto x1 = std::thread(throwNoThrow);
#endif
    x1.join();
}

Conclusion It is unspecified but it seems that the handler is always be called in the thread that causes std::terminate to be called. (tested on gcc-5.4, gcc-7.1, clang-3.8 with pthreads)