[Eager] Support eager hook_for_layer (#39531)

* Update comment

* [Eager] Support test_imperative_hook_for_layer with _test_eager_guard()

* Polish code name style

* Fix a error name

* Polish code, make it clear and simple

python/paddle/fluid/dygraph/layers.py

@@ -342,7 +342,7 @@ class Layer(object):
                 import paddle
                 import numpy as np
 
-                # the forward_post_hook change the input of the layer: input = input * 2
+                # the forward_pre_hook change the input of the layer: input = input * 2
                 def forward_pre_hook(layer, input):
                     # user can use layer and input for information statistis tasks
 

python/paddle/fluid/tests/unittests/test_imperative_hook_for_layer.py

-# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -25,14 +25,15 @@ import paddle.fluid.core as core
 import paddle.fluid.dygraph.base as base
 
 from test_imperative_lod_tensor_to_selected_rows import SimpleNet
+from paddle.fluid.framework import _test_eager_guard
 
-call_forward_hook = False
+call_forward_post_hook = False
 call_forward_pre_hook = False
 
 
-def forward_hook(layer, input, output):
-    global call_forward_hook
-    call_forward_hook = True
+def forward_post_hook(layer, input, output):
+    global call_forward_post_hook
+    call_forward_post_hook = True
 
 
 def forward_pre_hook(layer, input):
@@ -40,7 +41,7 @@ def forward_pre_hook(layer, input):
     call_forward_pre_hook = True
 
 
-def forward_hook1(layer, input, output):
+def forward_post_hook1(layer, input, output):
     return output * 2
 
 
@@ -50,8 +51,8 @@ def forward_pre_hook1(layer, input):
 
 
 class Test_Forward_Hook(unittest.TestCase):
-    # test forward_pre_hook and forward_hook that have return value
-    def test_forward_hook_return_value(self):
+    # test forward_pre_hook and forward_post_hook that have return value
+    def func_forward_hook_return_value(self):
         seed = 90
 
         places = [fluid.CPUPlace()]
@@ -104,23 +105,23 @@ class Test_Forward_Hook(unittest.TestCase):
                 self.assertTrue(
                     np.array_equal(outs_pre_hook.numpy(), outs_origin.numpy()))
 
-                # register forward_hook
-                forward_hook_handle1 = simplenet.register_forward_post_hook(
-                    forward_hook1)
+                # register forward_posst_hook
+                forward_post_hook_handle1 = simplenet.register_forward_post_hook(
+                    forward_post_hook1)
                 outs_forward_hook = simplenet(input, y)
                 self.assertTrue(
                     np.array_equal(outs_forward_hook.numpy(),
                                    outs_origin.numpy() * 2))
 
-                # remove forward_hook
-                forward_hook_handle1.remove()
+                # remove forward_post_hook
+                forward_post_hook_handle1.remove()
                 outs_forward_hook = simplenet(input, y)
                 self.assertTrue(
                     np.array_equal(outs_forward_hook.numpy(),
                                    outs_origin.numpy()))
 
-    # test forward_pre_hook and forward_hook that don't have return value
-    def test_forward_hook(self):
+    # test forward_pre_hook and forward_post_hook that don't have return value
+    def func_forward_hook(self):
         seed = 90
 
         places = [fluid.CPUPlace()]
@@ -133,7 +134,7 @@ class Test_Forward_Hook(unittest.TestCase):
                 fluid.default_main_program().random_seed = seed
                 fluid.set_flags({'FLAGS_sort_sum_gradient': True})
 
-                global call_forward_hook
+                global call_forward_post_hook
                 global call_forward_pre_hook
 
                 input_word = np.array(
@@ -158,38 +159,45 @@ class Test_Forward_Hook(unittest.TestCase):
 
                 # origin, don't register any hook
                 outs_origin = simplenet(input, y)
-                self.assertFalse(call_forward_hook)
+                self.assertFalse(call_forward_post_hook)
                 self.assertFalse(call_forward_pre_hook)
 
-                # register forward_hook and forward_pre_hook
-                forward_hook_handle = simplenet.register_forward_post_hook(
-                    forward_hook)
+                # register forward_post_hook and forward_pre_hook
+                forward_post_hook_handle = simplenet.register_forward_post_hook(
+                    forward_post_hook)
                 forward_pre_hook_handle = simplenet.register_forward_pre_hook(
                     forward_pre_hook)
                 outs_hook = simplenet(input, y)
-                self.assertTrue(call_forward_hook)
+                self.assertTrue(call_forward_post_hook)
                 self.assertTrue(call_forward_pre_hook)
 
                 outs_hook = simplenet(input, y)
-                self.assertTrue(call_forward_hook)
+                self.assertTrue(call_forward_post_hook)
                 self.assertTrue(call_forward_pre_hook)
 
-                # remove forward_hook
-                forward_hook_handle.remove()
-                call_forward_hook = False
+                # remove forward_post_hook
+                forward_post_hook_handle.remove()
+                call_forward_post_hook = False
                 call_forward_pre_hook = False
                 outs_remove_forward_hook = simplenet(input, y)
-                self.assertFalse(call_forward_hook)
+                self.assertFalse(call_forward_post_hook)
                 self.assertTrue(call_forward_pre_hook)
 
                 # remove forward_pre_hook
                 forward_pre_hook_handle.remove()
-                call_forward_hook = False
+                call_forward_post_hook = False
                 call_forward_pre_hook = False
                 outs_remove_hook = simplenet(input, y)
-                self.assertFalse(call_forward_hook)
+                self.assertFalse(call_forward_post_hook)
                 self.assertFalse(call_forward_pre_hook)
 
+    def test_forward_hook_return_value(self):
+        with _test_eager_guard():
+            self.func_forward_hook()
+            self.func_forward_hook_return_value()
+        self.func_forward_hook()
+        self.func_forward_hook_return_value()
+
 
 if __name__ == '__main__':
     unittest.main()