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https://issues.apache.org/jira/browse/HDFS-13121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16535401#comment-16535401
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Wei-Chiu Chuang commented on HDFS-13121:
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Sorry for coming to this late.
I don't have anything in mind to improve it better than what you have, and it
is already better than before. We could improve the handling if the situation
is hit again. So +1 and will commit the patch v04.
> 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,
> HDFS-13121.03.patch, HDFS-13121.04.patch, test-only.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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