dipeshmr1 commented on PR #54058:
URL: https://github.com/apache/spark/pull/54058#issuecomment-4643162085
> I might be missing something, but from my reading the code change itself
makes sense.
>
> I had one question about the added test: `Option(null)` becomes `None` in
Scala, and there is already a `None` case just above it. So I’m not sure the
new assertion exercises the same path as the original issue.
>
> Was the original issue from the instance `metrics()` method creating
`Some(null)`? If so, would it be useful to cover that path directly?
The key is the Scala default initialization. private var
latestPartitionOffsets: PartitionOffsetMap = _ — in Scala, = _ for a reference
type initializes to null.
The field is only assigned inside latestOffset(start, readLimit) (line
140). The metrics() instance method (line 347) is called by the streaming
engine for progress
reporting, independently of the trigger lifecycle.
So latestPartitionOffsets is null in exactly one scenario: at stream
startup, before the first latestOffset() call has completed. The sequence is:
Stream starts
→ latestPartitionOffsets = null (default)
→ streaming engine calls metrics() for progress reporting ← NPE here
(before fix)
→ latestOffset() runs → latestPartitionOffsets gets assigned
→ planInputPartitions() runs (line 269 has an assert confirming it's
non-null by now)
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