fix exception in BlobObject __del__ (#3742)

* fix exception in BlobObject __del__

* address comments
Co-authored-by: Noneflow-bot <69100618+oneflow-bot@users.noreply.github.com>

oneflow/init.py

@@ -59,9 +59,11 @@ import oneflow.python_gen.__export_symbols__
 
 import atexit
 import oneflow.python.framework.c_api_util
+import oneflow.python.framework.python_interpreter_util
 
 atexit.register(oneflow.python.framework.c_api_util.DestroyEnv)
 atexit.register(oneflow.python.framework.session_context.TryCloseDefaultSession)
+atexit.register(oneflow.python.framework.python_interpreter_util.SetShuttingDown)
 del atexit
 
 del absolute_import

oneflow/python/eager/object.py

@@ -15,6 +15,7 @@ limitations under the License.
 """
 from __future__ import absolute_import
 
+import oneflow.python.framework.python_interpreter_util as python_interpreter_util
 import oneflow.python.eager.symbol as symbol_util
 import oneflow
 
@@ -53,7 +54,11 @@ class BlobObject(Object):
     def add_releaser(self, release):
         self.release_.append(release)
 
-    def __del__(self):
+    # Bind `python_interpreter_util.IsShuttingDown` early.
+    # See the comments of `python_interpreter_util.IsShuttingDown`
+    def __del__(self, is_shutting_down=python_interpreter_util.IsShuttingDown):
+        if is_shutting_down():
+            return
         for release in self.release_:
             release(self)
         self.release_ = []

oneflow/python/framework/python_interpreter_util.py

+"""
+Copyright 2020 The OneFlow 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.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+"""
+It's copied from 
+https://github.com/numba/llvmlite/blob/3701287/llvmlite/binding/common.py
+"""
+import atexit
+
+
+# module globals may be cleared at shutdown,
+# so declare this variable as an array to avoid "global _shutting_down"
+_shutting_down = [False]
+
+
+def SetShuttingDown():
+    _shutting_down[0] = True
+
+
+def IsShuttingDown(_shutting_down=_shutting_down):
+    """
+    Whether the interpreter is currently shutting down.
+    For use in finalizers, __del__ methods, and similar; it is advised
+    to early bind this function rather than look it up when calling it,
+    since at shutdown module globals may be cleared.
+    """
+    return _shutting_down[0]