Close Core's channel when there is no reference to the channel

src/python/grpcio/grpc/_channel.py

@@ -1122,6 +1122,9 @@ class _ChannelCallState(object):
     def reset_postfork_child(self):
         self.managed_calls = 0
 
+    def __del__(self):
+        self.channel.close(cygrpc.StatusCode.cancelled, 'Channel deallocated!')
+
 
 def _run_channel_spin_thread(state):
 

src/python/grpcio_tests/tests_py3_only/unit/_leak_test.py

@@ -0,0 +1,93 @@
+# Copyright 2020 The gRPC Authors
+#
+# 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.
+"""A smoke test for memory leaks."""
+
+import logging
+import os
+import resource
+import sys
+import unittest
+from concurrent.futures import ThreadPoolExecutor
+
+import grpc
+
+_TEST_METHOD = '/test/Test'
+_REQUEST = b'\x23\x33'
+_LARGE_NUM_OF_ITERATIONS = 5000
+
+# If MAX_RSS inflated more than this size, the test is failed.
+_FAIL_THRESHOLD = 25 * 1024 * 1024  #  25 MiB
+
+
+def _get_max_rss():
+    return resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+
+
+def _pretty_print_bytes(x):
+    if x > 1024 * 1024 * 1024:
+        return "%.2f GiB" % (x / 1024.0 / 1024 / 1024)
+    elif x > 1024 * 1024:
+        return "%.2f MiB" % (x / 1024.0 / 1024)
+    elif x > 1024:
+        return "%.2f KiB" % (x / 1024.0)
+    else:
+        return "%d B" % x
+
+
+class _GenericHandler(grpc.GenericRpcHandler):
+
+    def service(self, handler_call_details):
+        if handler_call_details.method == _TEST_METHOD:
+            return grpc.unary_unary_rpc_method_handler(lambda x, _: x)
+
+
+def _start_a_test_server():
+    server = grpc.server(ThreadPoolExecutor(max_workers=1),
+                         options=(('grpc.so_reuseport', 0),))
+    server.add_generic_rpc_handlers((_GenericHandler(),))
+    port = server.add_insecure_port('localhost:0')
+    server.start()
+    return 'localhost:%d' % port, server
+
+
+def _perform_an_rpc(address):
+    channel = grpc.insecure_channel(address)
+    multicallable = channel.unary_unary(_TEST_METHOD)
+    response = multicallable(_REQUEST)
+    assert _REQUEST == response
+
+
+class TestLeak(unittest.TestCase):
+
+    def test_leak_with_single_shot_rpcs(self):
+        address, server = _start_a_test_server()
+
+        # Records memory before experiment.
+        before = _get_max_rss()
+
+        # Amplifies the leak.
+        for n in range(_LARGE_NUM_OF_ITERATIONS):
+            _perform_an_rpc(address)
+
+        # Fails the test if memory leak detected.
+        diff = _get_max_rss() - before
+        if diff > _FAIL_THRESHOLD:
+            self.fail("Max RSS inflated {} > {}".format(
+                _pretty_print_bytes(diff),
+                _pretty_print_bytes(_FAIL_THRESHOLD)))
+
+
+if __name__ == "__main__":
+    logging.basicConfig(level=logging.DEBUG)
+    unittest.main(verbosity=2)