Don't remove() TemporaryFile in __del__.

 * Not needed due at atexit mechanism at top of file.
 * Can't rely on complex functions from __del__ anyway.
 * Fixes warning message on my box:
       Exception ignored in: <function TempDirectory.__del__ at 0x12be10680>
       Traceback (most recent call last):
        File ".../tvm/python/tvm/contrib/util.py", line 55, in __del__
        File ".../tvm/python/tvm/contrib/util.py", line 51, in remove
        File "/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/lib/python3.7/shutil.py", line 509, in rmtree
        AttributeError: 'NoneType' object has no attribute 'path'

Author: areusch

python/tvm/contrib/util.py

@@ -15,6 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 """Common system utilities"""
+import atexit
 import os
 import tempfile
 import shutil
@@ -23,18 +24,25 @@
 except ImportError:
     fcntl = None
 
-
 class TempDirectory(object):
     """Helper object to manage temp directory during testing.
 
     Automatically removes the directory when it went out of scope.
     """
+
+    TEMPDIRS = []
+    @classmethod
+    def remove_tempdirs(cls):
+        for path in cls.TEMPDIRS:
+            shutil.rmtree(path, ignore_errors=True)
+
     def __init__(self, custom_path=None):
         if custom_path:
             os.mkdir(custom_path)
             self.temp_dir = custom_path
         else:
             self.temp_dir = tempfile.mkdtemp()
+            self.TEMPDIRS.append(self.temp_dir)
         self._rmtree = shutil.rmtree
 
     def remove(self):
@@ -43,9 +51,6 @@ def remove(self):
             self._rmtree(self.temp_dir, ignore_errors=True)
             self.temp_dir = None
 
-    def __del__(self):
-        self.remove()
-
     def relpath(self, name):
         """Relative path in temp dir
 
@@ -72,6 +77,9 @@ def listdir(self):
         return os.listdir(self.temp_dir)
 
 
+atexit.register(TempDirectory.remove_tempdirs)
+
+
 def tempdir(custom_path=None):
     """Create temp dir which deletes the contents when exit.