[GitHub] [arrow] pitrou commented on a diff in pull request #13176: ARROW-16597: [Python][FlightRPC] Force server shutdown at interpreter exit

[GitBox <gi...@apache.org>]

pitrou commented on code in PR #13176:
URL: https://github.com/apache/arrow/pull/13176#discussion_r884947195


##########
python/pyarrow/_flight.pyx:
##########
@@ -2516,6 +2517,32 @@ cdef class _ServerMiddlewareWrapper(ServerMiddleware):
             instance.call_completed(exception)
 
 
+cdef class _FlightServerFinalizer(_Weakrefable):
+    """
+    A finalizer that shuts down the server on destruction.
+
+    See ARROW-16597. If the server is still active at interpreter
+    exit, the process may segfault.
+    """
+
+    cdef:
+        shared_ptr[PyFlightServer] server
+
+    def finalize(self):
+        cdef:
+            PyFlightServer* server = self.server.get()
+            CStatus status
+        if server == NULL:
+            return
+        with nogil:
+            status = server.Shutdown()
+        check_flight_status(status)
+        with nogil:
+            status = server.Wait()
+        check_flight_status(status)
+        self.server.reset()

Review Comment:
   `reset()` won't be called if there was an error above, could this be a problem?



##########
python/pyarrow/_flight.pyx:
##########
@@ -2550,11 +2577,13 @@ cdef class FlightServerBase(_Weakrefable):
     """
 
     cdef:
-        unique_ptr[PyFlightServer] server
+        shared_ptr[PyFlightServer] server
+        object _finalizer

Review Comment:
   Nit, but I don't think `cdef` members are exposed in Python, so could name it `finalizer`?



##########
python/pyarrow/tests/arrow_16597.py:
##########
@@ -0,0 +1,36 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+# This file is called from a test in test_flight.py.
+import time
+
+import pyarrow as pa
+import pyarrow.flight as flight
+
+
+class Server(flight.FlightServerBase):
+    def do_put(self, context, descriptor, reader, writer):
+        time.sleep(1)
+        raise flight.FlightCancelledError("")
+
+
+server = Server("grpc://localhost:0")

Review Comment:
   Nit: put this under a `if __name__ == "__main__"` guard?



##########
python/pyarrow/tests/test_flight.py:
##########
@@ -1993,6 +1993,11 @@ def test(read_all):
         descriptor = flight.FlightDescriptor.for_command(b"echo")
         writer, reader = client.do_exchange(descriptor)
         test(reader.read_all)
+        try:
+            writer.close()
+        except Exception:
+            # Silence the Cancelled/Interrupt exception

Review Comment:
   If we only want to silence a certain class of exceptions, can the `except` clause be more specific?



##########
python/pyarrow/_flight.pyx:
##########
@@ -2516,6 +2517,32 @@ cdef class _ServerMiddlewareWrapper(ServerMiddleware):
             instance.call_completed(exception)
 
 
+cdef class _FlightServerFinalizer(_Weakrefable):
+    """
+    A finalizer that shuts down the server on destruction.
+
+    See ARROW-16597. If the server is still active at interpreter
+    exit, the process may segfault.
+    """
+
+    cdef:
+        shared_ptr[PyFlightServer] server
+
+    def finalize(self):
+        cdef:
+            PyFlightServer* server = self.server.get()
+            CStatus status
+        if server == NULL:
+            return
+        with nogil:
+            status = server.Shutdown()
+        check_flight_status(status)
+        with nogil:
+            status = server.Wait()
+        check_flight_status(status)

Review Comment:
   Is it instead possible to write this?
   ```suggestion
           with nogil:
               status = server.Shutdown() & server.Wait()
           check_flight_status(status)
   ```



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