[GitHub] [spark] juliuszsompolski commented on a diff in pull request #42929: [SPARK-45167][CONNECT][PYTHON] Python client must call `release_all`

["juliuszsompolski (via GitHub)" <gi...@apache.org>]

juliuszsompolski commented on code in PR #42929:
URL: https://github.com/apache/spark/pull/42929#discussion_r1329071826


##########
python/pyspark/sql/connect/client/reattach.py:
##########
@@ -53,7 +55,30 @@ class ExecutePlanResponseReattachableIterator(Generator):
     ReleaseExecute RPCs that instruct the server to release responses that it already processed.
     """
 
-    _release_thread_pool = ThreadPool(os.cpu_count() if os.cpu_count() else 8)
+    # Lock to manage the pool
+    _lock: ClassVar[RLockBase] = RLock()
+    _release_thread_pool: Optional[ThreadPool] = ThreadPool(os.cpu_count() if os.cpu_count() else 8)
+
+    @classmethod
+    def shutdown(cls: Type["ExecutePlanResponseReattachableIterator"]) -> None:
+        """
+        When the channel is closed, this method will be called before, to make sure all
+        outstanding calls are closed.
+        """
+        with cls._lock:
+            if cls._release_thread_pool is not None:
+                cls._release_thread_pool.close()
+                cls._release_thread_pool.join()
+                cls._release_thread_pool = None

Review Comment:
   I've seen (and ignored for now...) the scala equivalent of this failing when we do `SparkConnectClient.shutdown`, which does `channel.shutdownNow()`. In scala, we don't have a dedicated threadpool for that, but (ab)use a grpc thread in  https://github.com/databricks/runtime/blob/master/connector/connect/common/src/main/scala/org/apache/spark/sql/connect/client/ExecutePlanResponseReattachableIterator.scala#L179
   I wounder if more graceful shutdown of the channel would fixed it?



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