Russole commented on code in PR #10690:
URL: https://github.com/apache/ozone/pull/10690#discussion_r3549730269
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hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/ha/io/ScmListCodec.java:
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@@ -69,6 +69,12 @@ public Object deserialize(ByteString value) throws
InvalidProtocolBufferExceptio
"Missing ListArgument.type: " + argument);
}
+ // Empty list was serialized with type=Object.class.getName() as a
sentinel.
+ // Skip element-type resolution — there are no elements to decode.
+ if (argument.getValueCount() == 0) {
+ return new ArrayList<>();
Review Comment:
I think returning `Collections.emptyList()` can break replay for replicated
methods whose parameter type is `ArrayList`.
For example, `DeletedBlockLogStateManager` declares methods like
`addTransactionsToDB(ArrayList<DeletedBlocksTransaction> txs, ...)`. During
decode, `SCMRatisRequest.decode()` stores the deserialized list in the
`Object[]` arguments, and the generated `DeletedBlockLogStateManagerInvoker`
later casts it back with `(ArrayList) p[0]`.
For non-empty lists, `ScmListCodec.deserialize()` returns a new `ArrayList`,
so the cast works. With this change, empty lists return
`Collections.emptyList()` (`Collections$EmptyList`), which is not an
`ArrayList`, so replay can fail with `ClassCastException`.
Should this return `new ArrayList<>()` instead to preserve the runtime type
expected by the existing generated invokers?
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