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https://issues.apache.org/jira/browse/HDFS-13121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16490991#comment-16490991
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Zsolt Venczel commented on HDFS-13121:
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Thank you [~mackrorysd] for the review!
I've updated the patch with the extended description you suggested and I also
managed to create a test method that recreates the issue.
> NPE when request file descriptors when SC read
> ----------------------------------------------
>
> Key: HDFS-13121
> URL: https://issues.apache.org/jira/browse/HDFS-13121
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Gang Xie
> Assignee: Zsolt Venczel
> Priority: Minor
> Attachments: HDFS-13121.01.patch, HDFS-13121.02.patch
>
>
> Recently, we hit an issue that the DFSClient throws NPE. The case is that,
> the app process exceeds the limit of the max open file. In the case, the
> libhadoop never throw and exception but return null to the request of fds.
> But requestFileDescriptors use the returned fds directly without any check
> and then NPE.
>
> We need add a sanity check here of null pointer.
>
> private ShortCircuitReplicaInfo requestFileDescriptors(DomainPeer peer,
> Slot slot) throws IOException {
> ShortCircuitCache cache = clientContext.getShortCircuitCache();
> final DataOutputStream out =
> new DataOutputStream(new BufferedOutputStream(peer.getOutputStream()));
> SlotId slotId = slot == null ? null : slot.getSlotId();
> new Sender(out).requestShortCircuitFds(block, token, slotId, 1,
> failureInjector.getSupportsReceiptVerification());
> DataInputStream in = new DataInputStream(peer.getInputStream());
> BlockOpResponseProto resp = BlockOpResponseProto.parseFrom(
> PBHelperClient.vintPrefixed(in));
> DomainSocket sock = peer.getDomainSocket();
> failureInjector.injectRequestFileDescriptorsFailure();
> switch (resp.getStatus()) {
> case SUCCESS:
> byte buf[] = new byte[1];
> FileInputStream[] fis = new FileInputStream[2];
> {color:#d04437}sock.recvFileInputStreams(fis, buf, 0, buf.length);{color}
> ShortCircuitReplica replica = null;
> try {
> ExtendedBlockId key =
> new ExtendedBlockId(block.getBlockId(), block.getBlockPoolId());
> if (buf[0] == USE_RECEIPT_VERIFICATION.getNumber()) {
> LOG.trace("Sending receipt verification byte for slot {}", slot);
> sock.getOutputStream().write(0);
> }
> {color:#d04437}replica = new ShortCircuitReplica(key, fis[0], fis[1],
> cache,{color}
> {color:#d04437} Time.monotonicNow(), slot);{color}
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