fix(iota-indexer): deadlock when fetching from HttpRestKvClient in some scenarios #9508
Description
The deadlock issue is originated from this method when we provide as input an empty vector :
async fn multi_fetch(&self, uris: Vec<Key>) -> Vec<IndexerResult<Option<Bytes>>> {
let len = uris.len();
let fetches = stream::iter(uris.into_iter().map(|url| self.fetch(url)));
fetches.buffered(len).collect::<Vec<_>>().await
}This is because of buffered(len) which in this case is 0, it adds a side effect. By checking the buffered implementation I noticed that internally the len value is mapped to *this.max, so the while loop will not be executed halting the whole process since no futures are polled.
// First up, try to spawn off as many futures as possible by filling up
// our queue of futures.
while this.in_progress_queue.len() < *this.max {
match this.stream.as_mut().poll_next(cx) {
Poll::Ready(Some(fut)) => this.in_progress_queue.push_back(fut),
Poll::Ready(None) | Poll::Pending => break,
}
}As a solution we could return early if we receive and empty vector or the buffered len we provide as a constant in the multi_fetch method.