dajac commented on a change in pull request #9878:
URL: https://github.com/apache/kafka/pull/9878#discussion_r662847775



##########
File path: 
clients/src/main/java/org/apache/kafka/common/internals/KafkaFutureImpl.java
##########
@@ -247,17 +138,32 @@ public boolean completeExceptionally(Throwable 
newException) {
      */
     @Override
     public synchronized boolean cancel(boolean mayInterruptIfRunning) {
-        return completeExceptionally(new CancellationException()) || exception 
instanceof CancellationException;
+        return completableFuture.cancel(mayInterruptIfRunning);
+    }
+
+    // We need to deal with differences between KF's historic API and the API 
of CF:
+    // CF#get() does not wrap CancellationException in ExecutionException (nor 
does KF).
+    // CF#get() always wraps the _cause_ of a CompletionException in 
ExecutionException (which KF does not).
+    //
+    // The semantics for KafkaFuture are that all exceptional completions of 
the future (via #completeExceptionally() or exceptions from dependants)
+    // manifest as ExecutionException, as observed via both get() and getNow().
+    private void maybeRewrapAndThrow(Throwable cause) {
+        if (cause instanceof CancellationException) {
+            throw (CancellationException) cause;
+        }
     }
 
     /**
      * Waits if necessary for this future to complete, and then returns its 
result.
      */
     @Override
     public T get() throws InterruptedException, ExecutionException {
-        SingleWaiter<T> waiter = new SingleWaiter<>();
-        addWaiter(waiter);
-        return waiter.await();
+        try {
+            return completableFuture.get();
+        } catch (ExecutionException e) {
+            maybeRewrapAndThrow(e.getCause());
+            throw e;

Review comment:
       How about defining two helper methods, one for each cases?
   * `private void maybeRewrapAndThrow(ExecutionException exception)`; and
   * `private void maybeRewrapAndThrow(CompletionException exception)`




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