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https://issues.apache.org/jira/browse/HBASE-26688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17483139#comment-17483139
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Yutong Xiao commented on HBASE-26688:
-------------------------------------
Right. And we have marked in release note.
> Threads shared EMPTY_RESULT may lead to unexpected client job down.
> -------------------------------------------------------------------
>
> Key: HBASE-26688
> URL: https://issues.apache.org/jira/browse/HBASE-26688
> Project: HBase
> Issue Type: Bug
> Components: Client
> Reporter: Yutong Xiao
> Assignee: Yutong Xiao
> Priority: Major
> Fix For: 2.5.0, 3.0.0-alpha-3, 2.4.10
>
>
> Currently, we use a pre-created EMPTY_RESULT in the ProtoBuf.util to reduce
> the object creation. But these objects could be shared by multi client
> threads. The Result#cellScannerIndex related methods could throw confusing
> exception and make the client job down. Could refine the logic of these
> methods.
> The precreated objects in ProtoBufUtil.java:
> {code:java}
> private final static Cell[] EMPTY_CELL_ARRAY = new Cell[]{};
> private final static Result EMPTY_RESULT = Result.create(EMPTY_CELL_ARRAY);
> final static Result EMPTY_RESULT_EXISTS_TRUE = Result.create(null, true);
> final static Result EMPTY_RESULT_EXISTS_FALSE = Result.create(null, false);
> private final static Result EMPTY_RESULT_STALE =
> Result.create(EMPTY_CELL_ARRAY, null, true);
> {code}
> Result#advance
> {code:java}
> public boolean advance() {
> if (cells == null) return false;
> cellScannerIndex++;
> if (cellScannerIndex < this.cells.length) {
> return true;
> } else if (cellScannerIndex == this.cells.length) {
> return false;
> }
> // The index of EMPTY_RESULT could be incremented by multi threads and
> throw this exception.
> throw new NoSuchElementException("Cannot advance beyond the last cell");
> }
> {code}
> Result#current
> {code:java}
> public Cell current() {
> if (cells == null
> || cellScannerIndex == INITIAL_CELLSCANNER_INDEX
> || cellScannerIndex >= cells.length)
> return null;
> // Although it is almost impossible,
> // We can arrive here when the client threads share the common reused
> EMPTY_RESULT.
> return this.cells[cellScannerIndex];
> }
> {code}
> In this case, the client can easily got confusing exceptions even if they use
> different connections, tables in different threads.
> We should change the if condition cells == null to isEmpty() to avoid the
> client crashed from these exception.
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