pitrou commented on a change in pull request #9528:
URL: https://github.com/apache/arrow/pull/9528#discussion_r578685677
##########
File path: cpp/src/arrow/util/future.h
##########
@@ -515,15 +548,35 @@ class ARROW_MUST_USE_TYPE Future {
}
void DoMarkFinished(Result<ValueType> res) {
- SetResult(std::move(res));
-
- if (ARROW_PREDICT_TRUE(GetResult()->ok())) {
- impl_->MarkFinished();
+ const FutureState state = StateForResult(res);
+ if (impl_->stop_callback_.has_value()) {
+ struct ResultSetter {
+ Future<T>* fut;
+ Result<ValueType> res;
+
+ void operator()() { fut->SetResult(std::move(res)); }
+ };
+ impl_->MarkFinished(state, ResultSetter{this, std::move(res)});
} else {
- impl_->MarkFailed();
+ // The future cannot be cancelled concurrently as CancelOn()
+ // was not called.
+ SetResult(std::move(res));
+ impl_->MarkFinished(state);
}
Review comment:
Unfortunately, having the ability to cancel from one thread while
marking a future finished from another thread introduces some execution costs
inside the Future class. Here, we see that if some cancellation may occur, we
must synchronize result writing inside `FutureImpl::MarkFinished`.
cc @westonpace
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