westonpace commented on a change in pull request #11285:
URL: https://github.com/apache/arrow/pull/11285#discussion_r720450828
##########
File path: cpp/src/arrow/util/async_generator.h
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@@ -1645,6 +1667,47 @@ AsyncGenerator<T> MakeCancellable(AsyncGenerator<T>
source, StopToken stop_token
return CancellableGenerator<T>{std::move(source), std::move(stop_token)};
}
+template <typename T>
+struct PauseableGenerator {
+ public:
+ PauseableGenerator(AsyncGenerator<T> source,
std::shared_ptr<util::AsyncToggle> toggle)
+ : state_(std::make_shared<PauseableGeneratorState>(std::move(source),
+ std::move(toggle))) {}
+
+ Future<T> operator()() { return (*state_)(); }
+
+ private:
+ struct PauseableGeneratorState
+ : public std::enable_shared_from_this<PauseableGeneratorState> {
+ PauseableGeneratorState(AsyncGenerator<T> source,
+ std::shared_ptr<util::AsyncToggle> toggle)
+ : source_(std::move(source)), toggle_(std::move(toggle)) {}
+
+ Future<T> operator()() {
+ std::shared_ptr<PauseableGeneratorState> self = this->shared_from_this();
+ return toggle_->WhenOpen().Then([self] {
Review comment:
Yes, the generator can reorder things. If we want order we'd have to
rely on the future running callbacks in order (although that should be safe to
rely on). If we don't care about order we don't have to rely on that.
At the time I didn't think reordering would be a bad thing since exec plan
is likely to reorder stuff anyways but I don't really like it. I might take a
look to see if I can easily improve it.
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