pitrou commented on a change in pull request #9714:
URL: https://github.com/apache/arrow/pull/9714#discussion_r595142461
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File path: cpp/src/arrow/util/async_generator.h
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@@ -336,6 +345,68 @@ class ReadaheadGenerator {
std::queue<Future<T>> readahead_queue_;
};
+template <typename T>
+class PushGenerator {
+ struct State {
+ util::Mutex mutex;
+ std::deque<Result<T>> result_q;
+ util::optional<Future<T>> consumer_fut;
+ bool finished = false;
+ };
+
+ struct Generator {
+ const std::shared_ptr<State> state_;
+
+ Future<T> operator()() {
+ auto lock = state_->mutex.Lock();
+ assert(!state_->consumer_fut.has_value()); // Non-reentrant
+ if (!state_->result_q.empty()) {
+ auto fut =
Future<T>::MakeFinished(std::move(state_->result_q.front()));
+ state_->result_q.pop_front();
+ return fut;
+ }
+ if (state_->finished) {
+ return AsyncGeneratorEnd<T>();
+ }
+ auto fut = Future<T>::Make();
+ state_->consumer_fut = fut;
+ return fut;
+ }
+ };
+
+ public:
+ PushGenerator() : state_(std::make_shared<State>()) {}
+
+ void Push(Result<T> result) {
+ auto lock = state_->mutex.Lock();
+ if (state_->consumer_fut.has_value()) {
+ auto fut = std::move(state_->consumer_fut.value());
Review comment:
Well, the problem is that
https://en.cppreference.com/w/cpp/utility/optional/value doesn't specify if the
rvalue-this variant would really reset the `optional` itself, or just the
embedded value. It may depend on the actual embedded type. So it seems safer to
reset the `optional` explicitly.
@bkietz What do you think?
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