gianm commented on code in PR #20074:
URL: https://github.com/apache/druid/pull/20074#discussion_r3992125456
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processing/src/main/java/org/apache/druid/common/asyncresource/AsyncResources.java:
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@@ -98,24 +98,30 @@ public void onFailure(Throwable t)
* Returns an {@link AsyncResource} backed by a {@link ListenableFuture}
whose result <b>owns a lifecycle</b>: it
* becomes ready when the future completes, exposing the result via {@link
AsyncResource#get()}, and the result is
* managed as a {@link Closeable}. Closing the resource closes the result,
and a result that completes <i>after</i>
- * the resource was already closed (a cancel/close-vs-completion race) is
closed rather than leaked. Closing the
- * returned resource before the future completes cancels the future ({@code
cancel(true)}).
+ * the resource was already closed is closed rather than leaked.
+ *
+ * <p>Closing the returned resource deliberately does <b>not</b> cancel the
future. Cancellation is what makes
+ * futures-of-closeables unsafe in the first place: a task that produces its
value anyway hands it to a canceled
+ * future, which drops it silently, and nothing is left to close it. Leaving
the future alone means the result
+ * always arrives through the callback below, which closes it when the
resource is already gone. The cost is that
+ * work already submitted runs to completion; a producer that wants real
cancellation should populate a
+ * {@link SettableAsyncResource} itself and give it a {@link
SettableAsyncResource#setCanceler canceler} that can
+ * abort safely.
*
* <p>This is the managed counterpart of {@link #fromFutureUnmanaged}; use
that for a future whose result is a plain
* value or a completion signal with no lifecycle.
*/
public static <T extends Closeable> AsyncResource<T>
fromFutureCloseable(final ListenableFuture<T> future)
{
final SettableAsyncResource<T> retVal = new SettableAsyncResource<>();
- retVal.setCanceler(() -> future.cancel(true));
Review Comment:
👍
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