Use set as data structure for trace ongoing calls

src/python/grpcio/grpc/experimental/aio/_channel.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 """Invocation-side implementation of gRPC Asyncio Python."""
 import asyncio
-from typing import Any, AsyncIterable, Optional, Sequence, Text
+from typing import Any, AsyncIterable, Optional, Sequence, Set, Text
 
 import logging
 import grpc
@@ -37,18 +37,18 @@ _LOGGER = logging.getLogger(__name__)
 class _OngoingCalls:
     """Internal class used for have visibility of the ongoing calls."""
 
-    _calls: Sequence[_base_call.RpcContext]
+    _calls: Set[_base_call.RpcContext]
 
     def __init__(self):
-        self._calls = []
+        self._calls = set()
 
     def _remove_call(self, call: _base_call.RpcContext):
         self._calls.remove(call)
 
     @property
-    def calls(self) -> Sequence[_base_call.RpcContext]:
+    def calls(self) -> Set[_base_call.RpcContext]:
-        """Returns a shallow copy of the ongoing calls sequence."""
+        """Returns the set of ongoing calls."""
-        return self._calls[:]
+        return self._calls
 
     def size(self) -> int:
         """Returns the number of ongoing calls."""
@@ -56,7 +56,7 @@ class _OngoingCalls:
 
     def trace_call(self, call: _base_call.RpcContext):
         """Adds and manages a new ongoing call."""
-        self._calls.append(call)
+        self._calls.add(call)
         call.add_done_callback(self._remove_call)
 
 
@@ -398,7 +398,10 @@ class Channel:
             if not pending:
                 return
 
-        calls = self._ongoing_calls.calls
+        # A new set is created acting as a shallow copy because
+        # when cancellation happens the calls are automatically
+        # removed from the originally set.
+        calls = set(self._ongoing_calls.calls)
         for call in calls:
             call.cancel()
   

src/python/grpcio_tests/tests_aio/unit/close_channel_test.py

@@ -57,11 +57,11 @@ class TestOngoingCalls(unittest.TestCase):
         call = FakeCall()
         ongoing_calls.trace_call(call)
         self.assertEqual(ongoing_calls.size(), 1)
-        self.assertEqual(ongoing_calls.calls, [call])
+        self.assertEqual(ongoing_calls.calls, set([call]))
 
         call.callback(call)
         self.assertEqual(ongoing_calls.size(), 0)
-        self.assertEqual(ongoing_calls.calls, [])
+        self.assertEqual(ongoing_calls.calls, set())
 
 
 class TestCloseChannel(AioTestBase):