pitrou commented on a change in pull request #9613:
URL: https://github.com/apache/arrow/pull/9613#discussion_r587361262
##########
File path: cpp/src/arrow/io/caching.cc
##########
@@ -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:
Ideally this primitive would be globally available, instead of
reimplemented here. So you could write for example:
```c++
return Future::Gather(std::move(futures));
```
Also there may be different kinds of "gather". By default you probably want
to first error to immediately mark the resulting future errored.
cc @westonpace
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