tombentley commented on a change in pull request #9878:
URL: https://github.com/apache/kafka/pull/9878#discussion_r662837733
##########
File path:
clients/src/main/java/org/apache/kafka/common/internals/KafkaFutureImpl.java
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@@ -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:
I agree it's a bit messy, but I don't think that works. The call site in
`getNow()` differs from the others:
1. It's catching `CompletionException`, not `ExecutionException`
2. In the case there `maybeRewrapAndThrow` didn't throw it needs to wrap the
cause in an `ExceptionException`, unlike the other call sites, to conform with
the historical API of KafkaFuture.
The first would require `maybeRewrapAndThrow()` to have an `Exception`-typed
parameter, which, being a checked exception, means we'd need either to declare
`throws Exception`, or we'd need to type cast within `maybeRewrapAndThrow()`
and be left with an `else` case to deal with.
The second is difficult to abstract over nicely for the other call sites:
We'd need to pass a boolean to indicate whether the `ExceptionException` was
needed.
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