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https://issues.apache.org/jira/browse/HDFS-17552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17867293#comment-17867293
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ASF GitHub Bot commented on HDFS-17552:
---------------------------------------

szetszwo commented on code in PR #6888:
URL: https://github.com/apache/hadoop/pull/6888#discussion_r1684232744


##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java:
##########
@@ -96,6 +96,8 @@ public class Client implements AutoCloseable {
   private static final ThreadLocal<Integer> retryCount = new 
ThreadLocal<Integer>();
   private static final ThreadLocal<Object> EXTERNAL_CALL_HANDLER
       = new ThreadLocal<>();
+  public static final ThreadLocal<CompletableFuture<Object>> 
CALL_FUTURE_THREAD_LOCAL
+      = new ThreadLocal<>();
   private static final ThreadLocal<AsyncGet<? extends Writable, IOException>>
       ASYNC_RPC_RESPONSE = new ThreadLocal<>();

Review Comment:
   There is already a field `ASYNC_RPC_RESPONSE`.  Please replace it with 
`CompletableFuture` instead of adding a new field.





> [ARR] IPC client uses CompletableFuture to support asynchronous operations.
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-17552
>                 URL: https://issues.apache.org/jira/browse/HDFS-17552
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Jian Zhang
>            Assignee: Jian Zhang
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HDFS-17552.patch
>
>
> h3. Description
> In the implementation of asynchronous Ipc.client, the main methods used 
> include HADOOP-13226, HDFS-10224, etc.
> However, the existing implementation does not support `CompletableFuture`; 
> instead, it relies on setting up callbacks, which can lead to the "callback 
> hell" problem. Using `CompletableFuture` can better organize asynchronous 
> callbacks. Therefore, on the basis of the existing implementation, by using 
> `CompletableFuture`, once the `client.call` is completed, the asynchronous 
> thread handles the response of this call without blocking the main thread.
>  
> *Test*
> new UT  TestAsyncIPC#testAsyncCallWithCompletableFuture()



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