Thread join cause a segmentation fault when another thread is running

I have this method :

void Process::launch()
{
  std::thread readThread(&Process::readInfo, this);
  std::thread writeThread(&Process::writeInfo, this);

  readThread.join();
  this->_finished = true;
  writeThread.join();

  delete this->_namedPipeWrite;
  delete this->_namedPipeRead;
  std::cout << "No segmentation fault here" << std::endl;
  std::cout << "Segfault here" << std::endl;
  delete this->_threadPool;
  std::cout << "Never arrives here" << std::endl;
  _Exit(0);
}

Which segfault when I try to delete this->_threadPool

The deconstructor of threadPool do this :

 {
    std::unique_lock<std::mutex> lock(this->_mutex);

    this->_shutDown = true;
  }

  this->_cond.notify_all();

  for(std::thread &thread : this->_threadList)
  {
    thread.join();
  }

  this->_threadList.empty();
  this->_finished = true;
  delete this->_functionMutexes;

And the segfault occures at the join().

I declare my threadPool this way :

  this->_finished = false;
  this->_shutDown = false;
  this->_functionMutexes = new std::vector<std::mutex>(numberOfThreads);
  for(int i = 0; i < numberOfThreads; ++i)
  {
    this->_threadList.emplace_back(std::thread(&ThreadPool::task, this));
  }

This is the valgrind :

==28174== Process terminating with default action of signal 11 (SIGSEGV)
==28174==  Access not within mapped region at address 0x99CD9D0
==28174==    at 0x4E3D600: pthread_join (pthread_join.c:45)
==28174==    by 0x540EE46: std::thread::join() (in /usr/lib64/libstdc++.so.6.0.21)
==28174==    by 0x4063F0: ThreadPool<int>::shutDown() (ThreadPool.cpp:52)
==28174==    by 0x406299: ThreadPool<int>::~ThreadPool() (ThreadPool.cpp:21)
==28174==    by 0x410B62: Process::launch() (Process.cpp:56)
==28174==    by 0x410873: Process::Process(int) (Process.cpp:24)
==28174==    by 0x40CC87: ProcessManager::addOrder(std::__cxx11::list<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int) (in /home/danilo_d/Epitech-Projects/Semestre4/cpp_plazza/plazza)
==28174==    by 0x405934: main (in /home/danilo_d/Epitech-Projects/Semestre4/cpp_plazza/plazza)
==28174==  If you believe this happened as a result of a stack
==28174==  overflow in your program's main thread (unlikely but
==28174==  possible), you can try to increase the size of the
==28174==  main thread stack using the --main-stacksize= flag.
==28174==  The main thread stack size used in this run was 8388608.

This threadpool works fine, I already tested it.

There are some strange behaviour than happens.

-If I remove the line

  this->_writeThread = new std::thread(&Process::writeInfo, this);

and his join , I don't segfault.

-If I remove the delete this->_threadPool, I still segfaut but valgrind don't detect it.

Have any idea what can cause this ?