westonpace commented on a change in pull request #9613:
URL: https://github.com/apache/arrow/pull/9613#discussion_r587731880
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File path: cpp/src/arrow/io/caching.cc
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@@ -193,6 +195,36 @@ Result<std::shared_ptr<Buffer>>
ReadRangeCache::Read(ReadRange range) {
return Status::Invalid("ReadRangeCache did not find matching cache entry");
}
+Future<> ReadRangeCache::Wait() {
+ struct State {
+ explicit State(std::vector<Future<std::shared_ptr<Buffer>>> f)
+ : futures(std::move(f)), remaining(futures.size()) {}
+ std::vector<Future<std::shared_ptr<Buffer>>> futures;
+ std::atomic<size_t> remaining;
+ };
+
+ std::vector<Future<std::shared_ptr<Buffer>>> futures;
+ for (const auto& entry : impl_->entries) {
+ futures.push_back(entry.future);
+ }
+ auto out = Future<>::Make();
+ auto state = std::make_shared<State>(std::move(futures));
+ for (const auto& future : state->futures) {
+ future.AddCallback([state, out](const Result<std::shared_ptr<Buffer>>&)
mutable {
+ if (state->remaining.fetch_sub(1) != 1) return;
Review comment:
I wonder if it might be better to add `fail_fast` as an optional flag to
the existing method. We may someday want `Future<vector<Result<T>>>` but also
want the `fail_fast` behavior.
Also, just speculation, but I wonder if it would be possible to have a cast
(not sure if explicit or implicit) from Future<Any> -> Future<>. Under the
hood it could be `base.Then([] (const Result<T>& result) -> Status {return
Status::OK();})` (or perhaps there is a more efficient way to achieve the same
thing).
Then it could just be `static_cast<Future<>>(All(futures, Future::FailFast))`
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