code: def test_threadsafety(self):
      # Segfaults if the callback handling is not threadsafe
  
      errors = []
  
      def cb():
          # Sleep here to make it more likely for another thread
          # to call their callback at the same time.
          time.sleep(1e-3)
  
          # Check reentrancy
          r = self.module.t(lambda: 123)
          assert r == 123
  
          return 42
  
      def runner(name):
          try:
              for j in range(50):
                  r = self.module.t(cb)
                  assert r == 42
                  self.check_function(name)
          except Exception:
              errors.append(traceback.format_exc())
  
      threads = [
          threading.Thread(target=runner, args=(arg,))
          for arg in ("t", "t2")
          for n in range(20)
      ]
  
      for t in threads:
          t.start()
  
      for t in threads:
          t.join()
  
      errors = "\n\n".join(errors)
      if errors:
          raise AssertionError(errors)
  
imports: import math
  import textwrap
  import sys
  import pytest
  import threading
  import traceback
  import time
  import numpy
  from numpy.testing import IS_PYPY
  from .None import util
label_desc: Use image node_id 6 for calling the TestF77Callback obj's underlying member method code with example usage: obj.test_threadsafety() and returns: int