2021-12-23 hadoop3 写数据流程（三）：DataStreamer_hadoop datastreamer

1 概述

见名知意，此类主要用于数据传输，是一个守护线程，在创建DFSOutputStream的过程中被启动，启动之后再run方法之中使用一个while死循环（直到流或者客户端关闭）才停止运行，里面主要的逻辑是通过维护一个dataQueue队列，等待主线程往其中添加packet数据，等到添加了packet数据之后，会触发数据的发送，将数据发送到对应pipeline对应的dn之中，从而完成数据的传输。

2 源码分析

2.1 DataStreamer的前提调用

根据前文，在DFSOutputStream#newStreamForCreate中会创建对应的DFSOutputStream：

final DFSOutputStream out;
// 判断是否配置了ErasureCodingPolicy从而创建不同的DFSOutputStream对象
// 过程中会使用通过rpc远程创建INodeFile返回的HDFSFileStatus对象
if(stat.getErasureCodingPolicy() != null) {
    out = new DFSStripedOutputStream(dfsClient, src, stat,
                                     flag, progress, checksum, favoredNodes);
} else {
    out = new DFSOutputStream(dfsClient, src, stat,
                              flag, progress, checksum, favoredNodes, true);
}
// 启动往dn pipeline发送packet数据的的DataStreamer
out.start();

这里主要看非ErasureCoding一节，即创建DFSOutputStreamer

/** Construct a new output stream for creating a file. */
protected DFSOutputStream(DFSClient dfsClient, String src,
                          HdfsFileStatus stat, EnumSet<CreateFlag> flag, Progressable progress,
                          DataChecksum checksum, String[] favoredNodes, boolean createStreamer) {
    // 这里主要进行一些初始化的操作
    this(dfsClient, src, flag, progress, stat, checksum);
    this.shouldSyncBlock = flag.contains(CreateFlag.SYNC_BLOCK);
 
    // 参见下文关于此方法的解释，因为涉及到一张图，哈哈
    computePacketChunkSize(dfsClient.getConf().getWritePacketSize(),
                           bytesPerChecksum);
 
    // 在这里直接创建DataStreamer
    if (createStreamer) {
        streamer = new DataStreamer(stat, null, dfsClient, src, progress,
                                    checksum, cachingStrategy, byteArrayManager, favoredNodes,
                                    addBlockFlags);
    }
}
 
private DFSOutputStream(DFSClient dfsClient, String src,
                        EnumSet<CreateFlag> flag,
                        Progressable progress, HdfsFileStatus stat, DataChecksum checksum) {
    super(getChecksum4Compute(checksum, stat));
    this.dfsClient = dfsClient;
    this.src = src;
    this.fileId = stat.getFileId();
    this.blockSize = stat.getBlockSize();
    this.blockReplication = stat.getReplication();
    this.fileEncryptionInfo = stat.getFileEncryptionInfo();
    this.cachingStrategy = new AtomicReference<>(
        dfsClient.getDefaultWriteCachingStrategy());
    this.addBlockFlags = EnumSet.noneOf(AddBlockFlag.class);
    if (flag.contains(CreateFlag.NO_LOCAL_WRITE)) {
        this.addBlockFlags.add(AddBlockFlag.NO_LOCAL_WRITE);
    }
    if (flag.contains(CreateFlag.NO_LOCAL_RACK)) {
        this.addBlockFlags.add(AddBlockFlag.NO_LOCAL_RACK);
    }
    if (flag.contains(CreateFlag.IGNORE_CLIENT_LOCALITY)) {
        this.addBlockFlags.add(AddBlockFlag.IGNORE_CLIENT_LOCALITY);
    }
    if (progress != null) {
        DFSClient.LOG.debug("Set non-null progress callback on DFSOutputStream "
                            +"{}", src);
    }
 
    initWritePacketSize();
 
    this.bytesPerChecksum = checksum.getBytesPerChecksum();
    if (bytesPerChecksum <= 0) {
        throw new HadoopIllegalArgumentException(
            "Invalid value: bytesPerChecksum = " + bytesPerChecksum + " <= 0");
    }
    if (blockSize % bytesPerChecksum != 0) {
        throw new HadoopIllegalArgumentException("Invalid values: "
                                                 + HdfsClientConfigKeys.DFS_BYTES_PER_CHECKSUM_KEY
                                                 + " (=" + bytesPerChecksum + ") must divide block size (=" +
                                                 blockSize + ").");
    }
    this.byteArrayManager = dfsClient.getClientContext().getByteArrayManager();
}

下面解释下computePacketChunkSize

protected void computePacketChunkSize(int psize, int csize) {
    // 64Kb - packetHeader长度（33b，如下图）
    final int bodySize = psize - PacketHeader.PKT_MAX_HEADER_LEN;
    // getChecksumSize默认是使用crc32，即4b，csize默认是512b，因此chunkSize=516b
    final int chunkSize = csize + getChecksumSize();
    chunksPerPacket = Math.max(bodySize/chunkSize, 1);
    // packet的真实大小
    packetSize = chunkSize*chunksPerPacket;
    DFSClient.LOG.debug("computePacketChunkSize: src={}, chunkSize={}, "
            + "chunksPerPacket={}, packetSize={}",
        src, chunkSize, chunksPerPacket, packetSize);
  }

2.2 DataStreamer构造函数

没啥太多可介绍的，就是参数初始化
 
/**
   * construction with tracing info
   */
DataStreamer(HdfsFileStatus stat, ExtendedBlock block, DFSClient dfsClient,
             String src, Progressable progress, DataChecksum checksum,
             AtomicReference<CachingStrategy> cachingStrategy,
             ByteArrayManager byteArrayManage, String[] favoredNodes,
             EnumSet<AddBlockFlag> flags) {
    this(stat, block, dfsClient, src, progress, checksum, cachingStrategy,
         byteArrayManage, false, favoredNodes, flags);
    stage = BlockConstructionStage.PIPELINE_SETUP_CREATE;
}
 
private DataStreamer(HdfsFileStatus stat, ExtendedBlock block,
                     DFSClient dfsClient, String src,
                     Progressable progress, DataChecksum checksum,
                     AtomicReference<CachingStrategy> cachingStrategy,
                     ByteArrayManager byteArrayManage,
                     boolean isAppend, String[] favoredNodes,
                     EnumSet<AddBlockFlag> flags) {
    this.block = new BlockToWrite(block);
    this.dfsClient = dfsClient;
    this.src = src;
    this.progress = progress;
    this.stat = stat;
    this.checksum4WriteBlock = checksum;
    this.cachingStrategy = cachingStrategy;
    this.byteArrayManager = byteArrayManage;
    this.isLazyPersistFile = isLazyPersist(stat);
    this.isAppend = isAppend;
    this.favoredNodes = favoredNodes;
    final DfsClientConf conf = dfsClient.getConf();
    this.dfsclientSlowLogThresholdMs = conf.getSlowIoWarningThresholdMs();
    this.excludedNodes = initExcludedNodes(conf.getExcludedNodesCacheExpiry());
    this.errorState = new ErrorState(conf.getDatanodeRestartTimeout());
    this.addBlockFlags = flags;
}

2.3 run方法

由于这个对象实际上是一个线程，因此在DFSOutputStream#newStreamForCreate方法中最后启动start()方法时，就是调用线程的run方法执行操作（实在有点长。。。。）。

/*
   * streamer thread is the only thread that opens streams to datanode,
   * and closes them. Any error recovery is also done by this thread.
   */
@Override
public void run() {
    long lastPacket = Time.monotonicNow();
    TraceScope scope = null;
    // 死循环知道客户端或者流关闭
    while (!streamerClosed && dfsClient.clientRunning) {
        // if the Responder encountered an error, shutdown Responder
        if (errorState.hasError()) {
            closeResponder();
        }
 
        DFSPacket one;
        try {
            // process datanode IO errors if any
            boolean doSleep = processDatanodeOrExternalError();
 
            final int halfSocketTimeout = dfsClient.getConf().getSocketTimeout()/2;
            synchronized (dataQueue) {
                // wait for a packet to be sent.
                long now = Time.monotonicNow();
          /**
           * shouldRun：是否应该停止，根据流是否关闭、是否发生异常、是否客户端停止运行决定
           * dataQueue：最重要的一个变量，== 0表示还未开始写数据
           * stage：block的阶段
           * 现在距离上一个packet是否过去了指定客户端socket（60s）的一半
           * doSleep：数据流突然出现故障
           * 如果这些条件满足了，则让dataQueue休眠等待数据写入
           */
                while ((!shouldStop() && dataQueue.size() == 0 &&
                        (stage != BlockConstructionStage.DATA_STREAMING ||
                         now - lastPacket < halfSocketTimeout)) || doSleep) {
                    long timeout = halfSocketTimeout - (now-lastPacket);
                    timeout = timeout <= 0 ? 1000 : timeout;
                    timeout = (stage == BlockConstructionStage.DATA_STREAMING)?
                        timeout : 1000;
                    try {
                        dataQueue.wait(timeout);
                    } catch (InterruptedException  e) {
                        LOG.debug("Thread interrupted", e);
                    }
                    doSleep = false;
                    now = Time.monotonicNow();
                }
                if (shouldStop()) {
                    continue;
                }
                // get packet to be sent.
                // 获取需要发送的packet
                // 如果数据队列为空，那么先创建一个心跳packet（此心跳用于告知dn客户端仍存活），否则获取正常的数据packet
                if (dataQueue.isEmpty()) {
                    one = createHeartbeatPacket();
                } else {
                    try {
                        // 写入管道拥挤（客户端请求过于频繁）时，会进行一定的休眠
                        backOffIfNecessary();
                    } catch (InterruptedException e) {
                        LOG.debug("Thread interrupted", e);
                    }
                    one = dataQueue.getFirst(); // regular data packet
                    SpanId[] parents = one.getTraceParents();
                    if (parents.length > 0) {
                        scope = dfsClient.getTracer().
                            newScope("dataStreamer", parents[0]);
                        scope.getSpan().setParents(parents);
                    }
                }
            }
 
            // get new block from namenode.
            LOG.debug("stage={}, {}", stage, this);
 
            if (stage == BlockConstructionStage.PIPELINE_SETUP_CREATE) {
                // 此逻辑用于创建新文件
                LOG.debug("Allocating new block: {}", this);
                //nextBlockOutputStream()方法用来向Namenode 申请块信息，返回LocatedBlock 对象，
                // 其包含了 数据流pipeline 数据流节点信息 DatanodeInfo
                setPipeline(nextBlockOutputStream());
                // 初始化数据流，在其中会启动一个ResponseProcessor线程，此线程用来处理来自dn的响应
                // 所谓响应即ack，每当我们发出一个数据Packet，DataNode都需要发送ACK回复我们表示他收到了
                // 因此这样可以看出是每一个block对应一个响应线程，当此block写完关闭时，则会关闭此线程
                initDataStreaming();
            } else if (stage == BlockConstructionStage.PIPELINE_SETUP_APPEND) {
                // 此逻辑用于往文件添加数据
                LOG.debug("Append to block {}", block);
                // 这里也是创建一个dataStreamer
                setupPipelineForAppendOrRecovery();
                if (streamerClosed) {
                    continue;
                }
                // 初始化dataStream，在其中会启动一个ResponseProcessor线程，此线程用来处理来自dn的响应
                // 所谓响应即ack，每当我们发出一个数据Packet，DataNode都需要发送ACK回复我们表示他收到了
                initDataStreaming();
            }
 
            // 获取packet数据在block中的最后偏移量
            long lastByteOffsetInBlock = one.getLastByteOffsetBlock();
            if (lastByteOffsetInBlock > stat.getBlockSize()) {
                throw new IOException("BlockSize " + stat.getBlockSize() +
                                      " < lastByteOffsetInBlock, " + this + ", " + one);
            }
 
            // 判断是否是最后一个packet
            // 里面会等待所有lastPacket之前的Packet被确认。然后把流水线状态设置为关闭，
            // 但是此时还没有把lastPacket写到流水线上。
            if (one.isLastPacketInBlock()) {
                // wait for all data packets have been successfully acked
                synchronized (dataQueue) {
                    while (!shouldStop() && ackQueue.size() != 0) {
                        try {
                            // wait for acks to arrive from datanodes
                            // 等待从dn返回的ack
                            dataQueue.wait(1000);
                        } catch (InterruptedException  e) {
                            LOG.debug("Thread interrupted", e);
                        }
                    }
                }
                if (shouldStop()) {
                    continue;
                }
                // 指示pipeline关闭
                stage = BlockConstructionStage.PIPELINE_CLOSE;
            }
 
            // send the packet
            SpanId spanId = SpanId.INVALID;
            synchronized (dataQueue) {
                // move packet from dataQueue to ackQueue
                if (!one.isHeartbeatPacket()) {
                    if (scope != null) {
                        spanId = scope.getSpanId();
                        scope.detach();
                        one.setTraceScope(scope);
                    }
                    scope = null;
                    // 将此处理的packet移到ack队列中，指示这些packet处于等待被确认的过程中
                    dataQueue.removeFirst();
                    ackQueue.addLast(one);
                    packetSendTime.put(one.getSeqno(), Time.monotonicNow());
                    dataQueue.notifyAll();
                }
            }
 
            LOG.debug("{} sending {}", this, one);
 
            // write out data to remote datanode
            try (TraceScope ignored = dfsClient.getTracer().
                 newScope("DataStreamer#writeTo", spanId)) {
                // 将packet写入流水线中
                one.writeTo(blockStream);
                blockStream.flush();
            } catch (IOException e) {
                // HDFS-3398 treat primary DN is down since client is unable to
                // write to primary DN. If a failed or restarting node has already
                // been recorded by the responder, the following call will have no
                // effect. Pipeline recovery can handle only one node error at a
                // time. If the primary node fails again during the recovery, it
                // will be taken out then.
                // 用于标识当没有明显异常收到时，标记第一个dn为挂起而停止传输
                errorState.markFirstNodeIfNotMarked();
                throw e;
            }
            lastPacket = Time.monotonicNow();
 
            // update bytesSent
            long tmpBytesSent = one.getLastByteOffsetBlock();
            if (bytesSent < tmpBytesSent) {
                bytesSent = tmpBytesSent;
            }
 
            if (shouldStop()) {
                continue;
            }
 
            // Is this block full?
            // 通知当前block已经写完，从而等待acks
            if (one.isLastPacketInBlock()) {
                // wait for the close packet has been acked
                synchronized (dataQueue) {
                    while (!shouldStop() && ackQueue.size() != 0) {
                        dataQueue.wait(1000);// wait for acks to arrive from datanodes
                    }
                }
                if (shouldStop()) {
                    continue;
                }
 
                // 当一个块写完之后，需要添加新的块，会在上一个块end掉的时候（调用endBlock），
                // 把stage设置成PIPELINE_SETUP_CREATE，这样一来下次流水线也是被建立来创建新的块，达到添加块的目的。
                endBlock();
            }
            if (progress != null) { progress.progress(); }
 
            // This is used by unit test to trigger race conditions.
            if (artificialSlowdown != 0 && dfsClient.clientRunning) {
                Thread.sleep(artificialSlowdown);
            }
        } catch (Throwable e) {
            // Log warning if there was a real error.
            if (!errorState.isRestartingNode()) {
                // Since their messages are descriptive enough, do not always
                // log a verbose stack-trace WARN for quota exceptions.
                if (e instanceof QuotaExceededException) {
                    LOG.debug("DataStreamer Quota Exception", e);
                } else {
                    LOG.warn("DataStreamer Exception", e);
                }
            }
            lastException.set(e);
            assert !(e instanceof NullPointerException);
            errorState.setInternalError();
            if (!errorState.isNodeMarked()) {
                // Not a datanode issue
                streamerClosed = true;
            }
        } finally {
            if (scope != null) {
                scope.close();
                scope = null;
            }
        }
    }
    closeInternal();
}

2.4 nextBlockOutputStream

此方法再创建一个新块时被调用：

if (stage == BlockConstructionStage.PIPELINE_SETUP_CREATE) {
    // 此逻辑用于创建新文件
    LOG.debug("Allocating new block: {}", this);
    //nextBlockOutputStream()方法用来向Namenode 申请块信息，返回LocatedBlock 对象，
    // 其包含了 数据流pipeline 数据流节点信息 DatanodeInfo
    setPipeline(nextBlockOutputStream());
    // 初始化数据流，在其中会启动一个nextBlockOutputStream线程，此线程用来处理来自dn的响应
    // 所谓响应即ack，每当我们发出一个数据Packet，DataNode都需要发送ACK回复我们表示他收到了
    // 因此这样可以看出是每一个block对应一个响应线程，当此block写完关闭时，则会关闭此线程
    initDataStreaming();
} 

这个方法返回的是一个LocatedBlock，包含了一个块的信息。包括Block的备份存储位置，块的大小，块的BGS和BlockId。

/**
   * Open a DataStreamer to a DataNode so that it can be written to.
   * This happens when a file is created and each time a new block is allocated.
   * Must get block ID and the IDs of the destinations from the namenode.
   * Returns the list of target datanodes.
   */
protected LocatedBlock nextBlockOutputStream() throws IOException {
    LocatedBlock lb;
    DatanodeInfo[] nodes;
    StorageType[] nextStorageTypes;
    String[] nextStorageIDs;
    int count = dfsClient.getConf().getNumBlockWriteRetry();
    boolean success;
    final ExtendedBlock oldBlock = block.getCurrentBlock();
    // 循环创建一个新块，知道成功或者到达block写入的重试次数
    do {
        // 由于是创建新块，老块的异常就直接清除了
        errorState.resetInternalError();
        lastException.clear();
 
        // 不想将块副本保存到那些dn节点
        DatanodeInfo[] excluded = getExcludedNodes();
        // 创建一个新块，rpc调用namenode的addBlock操作
        lb = locateFollowingBlock(
            excluded.length > 0 ? excluded : null, oldBlock);
        // 设置一些基础信息，如当前块、传输数据量、密钥等
        block.setCurrentBlock(lb.getBlock());
        block.setNumBytes(0);
        bytesSent = 0;
        accessToken = lb.getBlockToken();
        nodes = lb.getLocations();
        nextStorageTypes = lb.getStorageTypes();
        nextStorageIDs = lb.getStorageIDs();
 
        // Connect to first DataNode in the list.
        // 建立和流水线上的第一个dn的连接
        // 这里会先建立一个pipeline的socket连接
        // 而后调用Sender#writeBlock方法通知那些包含在pipeline中的dn
        // 最后接受来自dn的回复，做后续的判断
        success = createBlockOutputStream(nodes, nextStorageTypes, nextStorageIDs,
                                          0L, false);
 
        if (!success) {
            LOG.warn("Abandoning " + block);
            dfsClient.namenode.abandonBlock(block.getCurrentBlock(),
                                            stat.getFileId(), src, dfsClient.clientName);
            block.setCurrentBlock(null);
            final DatanodeInfo badNode = nodes[errorState.getBadNodeIndex()];
            LOG.warn("Excluding datanode " + badNode);
            excludedNodes.put(badNode, badNode);
        }
    } while (!success && --count >= 0);
 
    if (!success) {
        throw new IOException("Unable to create new block.");
    }
    return lb;
}

2.5 ResponseProcessor线程

这是一个守护线程，用来处理来自dn的ack。DataNode接收到Packet后需要向客户端回复ACK，表示自己已经收到Packet了，而接收处理ACK的线程类就是ResponseProcessor。

对每一个块的传输都需要新建一个ResponseProcessor，当块传输完，客户端会通过endBlock方法间接地把当前ResponseProcessor销毁掉。下次传输新的Block的时候通过初始化传输环境方法initDataStreaming来间接地创建ResponseProcessor。

启动之后同样主要看run()方法呀：

@Override
public void run() {
 
    setName("ResponseProcessor for block " + block);
    // 创建一个代表ack的对象
    PipelineAck ack = new PipelineAck();
 
    TraceScope scope = null;
    // 循环接受ack，除非线程关闭、客户端停止运行、最后一个packet
    while (!responderClosed && dfsClient.clientRunning && !isLastPacketInBlock) {
        // process responses from datanodes.
        try {
            // read an ack from the pipeline
            // 从管道中读取ack
            ack.readFields(blockReplyStream);
            if (ack.getSeqno() != DFSPacket.HEART_BEAT_SEQNO) {
                Long begin = packetSendTime.get(ack.getSeqno());
                if (begin != null) {
                    long duration = Time.monotonicNow() - begin;
                    if (duration > dfsclientSlowLogThresholdMs) {
                        LOG.info("Slow ReadProcessor read fields for block " + block
                                 + " took " + duration + "ms (threshold="
                                 + dfsclientSlowLogThresholdMs + "ms); ack: " + ack
                                 + ", targets: " + Arrays.asList(targets));
                    }
                }
            }
 
            LOG.debug("DFSClient {}", ack);
 
            // 获取packet序号，在客户端和DataNode的通信中，数据是以Packet为单位进行传输的，每个packet的序号独一无二
            // 根据这个序号可以获知此ack对应那个packet
            // 序号是从0开始计数的，序号为-1的Packet是心跳包，客户端用他来告诉DataNode客户端还活着。
            // 序号为-2的包为未知包，收到这个包需要抛出异常
            long seqno = ack.getSeqno();
            // processes response status from datanodes.
            ArrayList<DatanodeInfo> congestedNodesFromAck = new ArrayList<>();
            for (int i = ack.getNumOfReplies()-1; i >=0  && dfsClient.clientRunning; i--) {
                // 从ack的header信息中获取对应的dn的状态
                final Status reply = PipelineAck.getStatusFromHeader(ack
                                                                     .getHeaderFlag(i));
                // 根据状态查看dn是否处于繁忙
                if (PipelineAck.getECNFromHeader(ack.getHeaderFlag(i)) ==
                    PipelineAck.ECN.CONGESTED) {
                    congestedNodesFromAck.add(targets[i]);
                }
                // Restart will not be treated differently unless it is
                // the local node or the only one in the pipeline.
                // 根据状态判断是否有dn处于重启过程中
                if (PipelineAck.isRestartOOBStatus(reply)) {
                    final String message = "Datanode " + i + " is restarting: "
                        + targets[i];
                    // 根据是否等待，如果等待将会把将当前传进来的节点标记为正在重启的节点
                    // 并且为他设置重启时限，把BadNode记录清除掉(这时的BadNode一般是流水线上第一个DataNode，
                    // BadNode指的是工作过程发生错误或者无法联系上的DataNode)
                    errorState.initRestartingNode(i, message,
                                                  shouldWaitForRestart(i));
                    throw new IOException(message);
                }
                // node error
                // 检查ACK的回应是否是SUCCESS，如果不是，表示对应的DataNode没有
                // 正常接收Packet，那么将把该DataNode标记为BadNode。
                if (reply != SUCCESS) {
                    errorState.setBadNodeIndex(i); // mark bad datanode
                    throw new IOException("Bad response " + reply +
                                          " for " + block + " from datanode " + targets[i]);
                }
            }
 
            // 将上面得到的繁忙节点加入到DataStreamer的成员变量congestedNodes中，
            // 这个变量用来标记所有繁忙节点，以便输出日志(DataStreamer的backIfNecessary)的时候观察哪些节点繁忙。
            if (!congestedNodesFromAck.isEmpty()) {
                synchronized (congestedNodes) {
                    congestedNodes.clear();
                    congestedNodes.addAll(congestedNodesFromAck);
                }
            } else {
                synchronized (congestedNodes) {
                    congestedNodes.clear();
                    lastCongestionBackoffTime = 0;
                }
            }
 
            assert seqno != PipelineAck.UNKOWN_SEQNO :
            "Ack for unknown seqno should be a failed ack: " + ack;
            if (seqno == DFSPacket.HEART_BEAT_SEQNO) {  // a heartbeat ack
                continue;
            }
 
            // a success ack for a data packet
            DFSPacket one;
            // ackQueue中存储的都是待确认的packet，如果数据包发出去之后流水线失败，
            // 得不到确认。数据包可以从ackQueue恢复，不至于以前的Packet丢失。
            synchronized (dataQueue) {
                one = ackQueue.getFirst();
            }
            // 收到的ACK的序号和ackQueue队头元素的序号一不一样，如果不一样，说明可能收发乱序了
            if (one.getSeqno() != seqno) {
                throw new IOException("ResponseProcessor: Expecting seqno " +
                                      one.getSeqno() + " for block " + block +
                                      " but received " + seqno);
            }
            isLastPacketInBlock = one.isLastPacketInBlock();
 
            // Fail the packet write for testing in order to force a
            // pipeline recovery.
            if (DFSClientFaultInjector.get().failPacket() &&
                isLastPacketInBlock) {
                failPacket = true;
                throw new IOException(
                    "Failing the last packet for testing.");
            }
 
            // update bytesAcked
            // getLastByteOffsetBlock其实就是最后一个包的结尾相对Block起始位置的偏移量。也就是现在写了的数据量。
            // offsetInBlock + dataPos - dataStart
            block.setNumBytes(one.getLastByteOffsetBlock());
 
            synchronized (dataQueue) {
                scope = one.getTraceScope();
                if (scope != null) {
                    scope.reattach();
                    one.setTraceScope(null);
                }
                lastAckedSeqno = seqno;
                pipelineRecoveryCount = 0;
                // 移除已经被确认的packet
                ackQueue.removeFirst();
                packetSendTime.remove(seqno);
                dataQueue.notifyAll();
 
                one.releaseBuffer(byteArrayManager);
            }
        } catch (Throwable e) {
            if (!responderClosed) {
                lastException.set(e);
                errorState.setInternalError();
                // 标记第一个dn为badNode，因为第一个建立连接，嫌疑最大
                errorState.markFirstNodeIfNotMarked();
                synchronized (dataQueue) {
                    dataQueue.notifyAll();
                }
                if (!errorState.isRestartingNode()) {
                    LOG.warn("Exception for " + block, e);
                }
                responderClosed = true;
            }
        } finally {
            if (scope != null) {
                scope.close();
            }
            scope = null;
        }
    }
}