gnodet-bot commented on code in PR #27921:
URL: https://github.com/apache/camel/pull/27921#discussion_r4289588426
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components/camel-resilience4j/src/main/java/org/apache/camel/component/resilience4j/ResilienceProcessor.java:
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@@ -845,10 +863,55 @@ private CompletableFuture<Exchange> processTaskAsync(
return future;
}
+ /**
+ * Makes the write-back of the task and the takeover by the caller (the
fallback, or the timeout exception) mutually
+ * exclusive, for one call. The task writes its result only if it claims
the exchange before the caller. The caller
+ * always writes: if it takes over while the write-back of the task is in
progress, it waits until that is done, and
+ * then works on the exchange that holds the result of the task.
+ */
+ private static final class ExchangeWriteGuard {
+ private final Lock lock = new ReentrantLock();
+ private boolean claimed;
+
+ /**
+ * Claims the exchange for the write-back of the task. When this
returns true, the lock is held until
+ * {@link #writeBackDone()} is called.
+ */
+ boolean tryClaimForWriteBack() {
+ lock.lock();
+ if (claimed) {
+ lock.unlock();
+ return false;
+ }
+ claimed = true;
+ return true;
+ }
+
+ /**
+ * Ends the write-back of the task, after {@link
#tryClaimForWriteBack()} returned true.
+ */
Review Comment:
`tryClaimForWriteBack()` returns `true` with the lock held — an accidental
call without a `writeBackDone()` `finally` block deadlocks the next caller
permanently. Document the contract:
```suggestion
/**
* Ends the write-back of the task, after {@link
#tryClaimForWriteBack()} returned true.
* Must be called in a {@code finally} block.
*/
```
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