code: def test_thread_safe(self):
      dev0 = cuda.Device(0)
      dev1 = cuda.Device(1)
  
      t0_setup = threading.Event()
      t1_setup = threading.Event()
      t0_first_exit = threading.Event()
  
      t0_exit_device = []
      t1_exit_device = []
  
      def t0_seq():
          with dev0:
              with dev0:
                  t0_setup.set()
                  t1_setup.wait()
              t0_exit_device.append(cuda.Device().id)
              t0_first_exit.set()
  
      def t1_seq():
          t0_setup.wait()
          with dev1:
              with dev0:
                  t1_setup.set()
                  t0_first_exit.wait()
              t1_exit_device.append(cuda.Device().id)
  
      t1 = threading.Thread(target=t1_seq)
      t1.start()
      t0_seq()
      t1.join()
      assert t0_exit_device[0] == 0
      assert t1_exit_device[0] == 1
  
imports: import re
  import threading
  import unittest
  import pytest
  import cupy
  from cupy import cuda
  from cupy import testing
label_desc: Use image node_id 6 for calling the TestDeviceSwitch obj's underlying member method code with example usage: obj.test_thread_safe() without return types