mas-chen commented on code in PR #20215:
URL: https://github.com/apache/flink/pull/20215#discussion_r947506841
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flink-connectors/flink-connector-base/src/main/java/org/apache/flink/connector/base/source/hybrid/HybridSourceReader.java:
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@@ -231,16 +236,7 @@ private void setCurrentReader(int index) {
reader.start();
currentSourceIndex = index;
currentReader = reader;
- currentReader
- .isAvailable()
- .whenComplete(
- (result, ex) -> {
- if (ex == null) {
- availabilityFuture.complete(result);
- } else {
- availabilityFuture.completeExceptionally(ex);
- }
- });
Review Comment:
If I understand the process in the alternative solution:
1. A new reader is set.
2. When the reader future is done, renew the future.
3. Complete the future when the current reader hits end of input
4. Repeat process
However, this doesn't solve the case where there is no end of input for the
streaming source. And to handle this case, there needs to be a process running
recursively outside of this reader switch handling method. And repeatedly
signaling completeness from the underlying reader and renewing again and again.
(This is why PR introduces the MultipleFuturesAvailabilityHelper to coordinate
this additional complexity)
Also in the code snippet above, I think there could be a need for
synchronization on the future variable, since `whenComplete()` would not be
guaranteed to run on the task thread, unless we use `whenCompleteAsync()` and
pass the task executor, which we don't have access to.
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