tombentley commented on a change in pull request #9878:
URL: https://github.com/apache/kafka/pull/9878#discussion_r662990335
##########
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:
There don't seem to be any good options here.
We could throw from a single method if you're willing to have the method
like this
```java
private <T, E extends Exception> T
throwUnwrappingCancellationException(E exception) throws E {
if (exception.getCause() instanceof CancellationException) {
throw (CancellationException) exception.getCause();
}
throw exception;
}
```
and the call sites to look like this:
```java
return throwUnwrappingCancellationException(e);
```
The `return <methodThatAlwaysThrows>` is nasty, and I can't think of a good
method name. Personally I don't think this is better than naming the current
method `maybeThrowCancellationException` as you suggest, and living with the
throw in two places, so I've gone with that.
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