rtpsw commented on code in PR #34392:
URL: https://github.com/apache/arrow/pull/34392#discussion_r1169726852
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cpp/src/arrow/acero/asof_join_node.cc:
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@@ -249,12 +250,18 @@ struct MemoStore {
void swap(MemoStore& memo) {
std::swap(no_future_, memo.no_future_);
- std::swap(current_time_, memo.current_time_);
+ current_time_ = memo.current_time_.exchange((OnType)current_time_);
entries_.swap(memo.entries_);
future_entries_.swap(memo.future_entries_);
times_.swap(memo.times_);
}
+ void UpdateTime(OnType ts) {
+ OnType prev_time = current_time_;
+ while (prev_time < ts && current_time_.compare_exchange_weak(prev_time,
ts)) {
Review Comment:
This is because `compare_and_exchange_weak` (see
[doc](https://en.cppreference.com/w/cpp/atomic/atomic/compare_exchange)) may
not find the expected value of `prev_time` from line 260 by the time the loop
is executed due to a race condition (expected to be rare). In this case `false`
is returned and `prev_time` is updated to the value of `current_time_`. Then,
another iteration is tried. This is normal CAS-loop logic.
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