code: def test_reentrant(self):
      # In/grad data are random; these do not simulate the actually possible
      # cases.
      # any function other than Exp is ok
      g = functions.math.identity.Identity()
  
      self.h.backward_preprocess(self.f, (self.x,), (self.gy,))
      t1 = _get_time()
      time.sleep(0.001)  # longer than each hook call
      self.h.forward_preprocess(g, (self.x,))
      self.h.forward_postprocess(g, (self.x,))
      t2 = _get_time()
      self.h.backward_postprocess(self.f, (self.x,), (self.gy,))
  
      history = dict(self.h.call_history)
      assert len(history) == 2
      assert self.f._impl_name in history
      assert g._impl_name in history
      f_time = history[self.f._impl_name]
      g_time = history[g._impl_name]
      assert g_time <= t2 - t1
      assert f_time >= t2 - t1
  
imports: import os
  import time
  import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import function_hooks
  from chainer import functions
  from chainer.functions.math import basic_math
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 8 for calling the TestTimerHookToFunction obj's underlying member method code with example usage: obj.test_reentrant() without return types