mumrah opened a new pull request, #12403:
URL: https://github.com/apache/kafka/pull/12403
In ControllerApis, we are making use of the CompletableFuture-s returned by
QuorumController to add callbacks via `whenComplete`. Since these chained
methods on CompletableFuture return a _new_ CompletableFuture instance, the
ControllerPurgatory does not capture any of downstream exceptions when
completing the original instance. The only way to see these errors is to call
`get` on the chained future, or to add additional completion stages to handle
the error explicitly. However, we do not want to call `get` since that would
block the request threads.
This patch changes the signature of the request handlers in ControllerApis
to all return CompletableFuture. It also converts all of the
`CompletableFuture#whenComplete` callbacks to `CompletableFuture#handle`. This
allows us to directly handle exceptions thrown by the controller in the
individual request handlers. A single `whenComplete` error handler is added in
`ControllerApis#handle` which will ensure we log exceptions thrown by the
response builders (or other logic in the chained `handle` calls).
The resulting future chain now looks like:
```scala
controller.doStuff()
.handle { (result, exception) =>
// Transform result or exception into a response
}
.whenComplete { (result, exception) =>
// Handle errors thrown in "handle"
}
```
The future is still completed by ControllerPurgatory, and that is when the
completion stages are run. We do not call `get` in ControllerApis to avoid
blocking the request threads.
There is some opportunity for cleanup and consolidation of error handling in
ControllerApis, but I'd rather make a separate PR for that.
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