pitrou commented on a change in pull request #9714:
URL: https://github.com/apache/arrow/pull/9714#discussion_r595143165
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File path: cpp/src/arrow/util/async_generator.h
##########
@@ -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());
+ state_->consumer_fut.reset();
+ lock.Unlock(); // unlock before potentially invoking a callback
+ fut.MarkFinished(std::move(result));
+ return;
+ }
+ state_->result_q.push_back(std::move(result));
+ }
+
+ void Close() {
+ auto lock = state_->mutex.Lock();
+ state_->finished = true;
+ if (state_->consumer_fut.has_value()) {
+ auto fut = std::move(state_->consumer_fut.value());
+ state_->consumer_fut.reset();
+ lock.Unlock(); // unlock before potentially invoking a callback
+ fut.MarkFinished(IterationTraits<T>::End());
+ }
+ }
+
+ /// Return a non-reentrant async generator
+ Generator generator() { return Generator{state_}; }
Review comment:
Yes, I don't know how to make this API homogenous with the rest. I'll
add comments anyway.
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