zookeeper源码(08)请求处理及数据读写流程

ServerCnxnFactory

用于接收客户端连接、管理客户端session、处理客户端请求。

ServerCnxn抽象类

代表一个客户端连接对象：

从网络读写数据
数据编解码
将请求转发给上层组件或者从上层组件接收响应
管理连接状态，比如：enableRecv、sessionTimeout、stale、invalid等
保存当前的packetsReceived、packetsSent、lastCxid、lastZxid等
继承了Watcher接口，也可以作为监听器

两个实现类：

NIOServerCnxn - 基于NIO
NettyServerCnxn - 基于Netty

NIOServerCnxnFactory

基于NIO的非阻塞、多线程的ServerCnxnFactory实现类，多线程之间通过queue通信：

1个accept线程，用来接收客户端连接，交给selector线程处理
1-N个selector线程，每个线程会select 1/N个连接，多个selector线程的原因是，由于有大量连接，select()可能会成为性能瓶颈
0-M个socket IO worker线程，做socket读写，如果配置为0则selector线程来做IO
1个清理线程，用于关闭空闲连接

线程数量分配示例：32核的机器，1accept线程，1个清理线程，4个selector线程，64个worker线程。

configure方法

不支持ssl
创建ConnectionExpirerThread线程

根据CPU核数确定各种线程的数量

int numCores = Runtime.getRuntime().availableProcessors();
// 32 cores sweet spot seems to be 4 selector threads
numSelectorThreads = Integer.getInteger(
    ZOOKEEPER_NIO_NUM_SELECTOR_THREADS,
    Math.max((int) Math.sqrt((float) numCores / 2), 1));

// 64
numWorkerThreads = Integer.getInteger(ZOOKEEPER_NIO_NUM_WORKER_THREADS, 2 * numCores);

创建SelectorThread线程
创建ServerSocketChannel、启动监听、设置非阻塞
创建AcceptThread线程

start方法

启动acceptThread、selectorThreads、workerPool、expirerThread线程。

acceptThread线程

1个accept线程，用来接收客户端连接，交给selector线程处理：

select查找acceptable的key

doAccept接受连接

if (key.isAcceptable()) {
    if (!doAccept()) {
        pauseAccept(10);
    }
}

给sc(SocketChannel)设置非阻塞、验证远程IP连接数不超过maxClientCnxns(60)、获取SelectorThread开始select读写事件

// Round-robin assign this connection to a selector thread
if (!selectorIterator.hasNext()) {
    selectorIterator = selectorThreads.iterator();
}
SelectorThread selectorThread = selectorIterator.next();
// 使用队列缓存SocketChannel
if (!selectorThread.addAcceptedConnection(sc)) {
    throw new IOException("Unable to add connection to selector queue");
}

selectorThread线程

run方法select读写事件、接受客户连接、为key注册"感兴趣"的事件：

run方法

public void run() {
    try {
        while (!stopped) {
            try {
                select(); // select读写事件
                processAcceptedConnections(); // 接受客户连接
                processInterestOpsUpdateRequests();
            } catch (RuntimeException e) {
            } catch (Exception e) {
            }
        }
    }
    // ...
}

接受客户连接会注册OP_READ、创建NIOServerCnxn、绑定到key上面

private void processAcceptedConnections() {
    SocketChannel accepted;
    while (!stopped && (accepted = acceptedQueue.poll()) != null) {
        SelectionKey key = null;
        try {
            key = accepted.register(selector, SelectionKey.OP_READ);
            NIOServerCnxn cnxn = createConnection(accepted, key, this);
            key.attach(cnxn); // 绑定到key上
            addCnxn(cnxn); // 维护连接层会话
        } catch (IOException e) {
            //  略
        }
    }
}

select到读写事件会交给handleIO方法处理

private void handleIO(SelectionKey key) {
    IOWorkRequest workRequest = new IOWorkRequest(this, key);
    NIOServerCnxn cnxn = (NIOServerCnxn) key.attachment();

    // Stop selecting this key while processing on its connection
    cnxn.disableSelectable();
    key.interestOps(0); // 重置感兴趣的事件，IO处理完成之后会重新注册读写事件
    touchCnxn(cnxn); // 维护连接层会话，刷新过期时间
    workerPool.schedule(workRequest); // workRequest.doWork方法做异步读写
}

为key注册"感兴趣"的事件

private void processInterestOpsUpdateRequests() {
    SelectionKey key;
    while (!stopped && (key = updateQueue.poll()) != null) {
        NIOServerCnxn cnxn = (NIOServerCnxn) key.attachment();
        if (cnxn.isSelectable()) {
            key.interestOps(cnxn.getInterestOps());
        }
    }
}

workRequest.doWork方法

workRequest是IOWorkRequest类型对象，doWork会read数据并传递给上层组件：

public void doWork() throws InterruptedException {
    // 略

    if (key.isReadable() || key.isWritable()) {
        cnxn.doIO(key); // 在workerPool线程上执行

        // 略
        touchCnxn(cnxn); // 维护连接层会话，刷新过期时间
    }

    // 略
}

数据包使用 len body 方式传输，read的过程不介绍了，cnxn在read到完整的数据之后会调用readConnectRequest或readRequest方法将数据传递给上层组件：

// 应用层建立连接
private void readConnectRequest() throws IOException, ClientCnxnLimitException {
    BinaryInputArchive bia = BinaryInputArchive.getArchive(new ByteBufferInputStream(incomingBuffer));
    // ConnectRequest封装:
    // protocolVersion(0), lastZxidSeen(0), timeOut(3s), sessionId(0), passwd(16位byte), readOnly(F)
    ConnectRequest request = protocolManager.deserializeConnectRequest(bia);
    zkServer.processConnectRequest(this, request);
    initialized = true;
}

protected void readRequest() throws IOException {
    RequestHeader h = new RequestHeader();
    // 请求头，封装客户端xid和type由客户端传递过来
    ByteBufferInputStream.byteBuffer2Record(incomingBuffer, h);
    // 转ByteBufferRequestRecord对象，封装请求字节流
    // readRecord将字节流反序列化为指定的Record实现类对象
    RequestRecord request = RequestRecord.fromBytes(incomingBuffer.slice());
    zkServer.processPacket(this, h, request);
}

NettyServerCnxnFactory

基于Netty的ServerCnxnFactory实现。

CnxnChannelHandler类

核心的网络层处理器，此处记录重要代码：

class CnxnChannelHandler extends ChannelDuplexHandler {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        final Channel channel = ctx.channel();
        // 略
        // 创建NettyServerCnxn绑定到channel
        NettyServerCnxn cnxn = new NettyServerCnxn(channel, zkServer, NettyServerCnxnFactory.this);
        ctx.channel().attr(CONNECTION_ATTRIBUTE).set(cnxn);

        // 略
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try {
            try {
                NettyServerCnxn cnxn = ctx.channel().attr(CONNECTION_ATTRIBUTE).get();
                if (cnxn == null) {
                    LOG.error("channelRead() on a closed or closing NettyServerCnxn");
                } else {
                    // 读取请求数据
                    cnxn.processMessage((ByteBuf) msg);
                }
            } catch (Exception ex) {
                throw ex;
            }
        } finally {
            ReferenceCountUtil.release(msg);
        }
    }
}

cnxn读取请求数据

void processMessage(ByteBuf buf) {
    if (throttled.get()) {
        // 略
    } else {
        if (queuedBuffer != null) {
            appendToQueuedBuffer(buf.retainedDuplicate());
            processQueuedBuffer();
        } else {
            receiveMessage(buf); // 解码逻辑在此方法中
            // Have to check !closingChannel, because an error in
            // receiveMessage() could have led to close() being called.
            if (!closingChannel && buf.isReadable()) {
                if (queuedBuffer == null) {
                    queuedBuffer = channel.alloc().compositeBuffer();
                }
                appendToQueuedBuffer(buf.retainedSlice(buf.readerIndex(), buf.readableBytes()));
            }
        }
    }
}

read到完整的数据之后会将数据传递给上层组件：

if (initialized) {
    RequestHeader h = new RequestHeader();
    ByteBufferInputStream.byteBuffer2Record(bb, h);
    RequestRecord request = RequestRecord.fromBytes(bb.slice());
    zks.processPacket(this, h, request);
} else {
    // 应用层建立连接
    BinaryInputArchive bia = BinaryInputArchive.getArchive(new ByteBufferInputStream(bb));
    ConnectRequest request = protocolManager.deserializeConnectRequest(bia);
    zks.processConnectRequest(this, request);
    initialized = true;
}

ZooKeeperServer处理方法

processConnectRequest方法处理连接请求

ZooKeeperServer的processConnectRequest方法用来处理连接请求：

public void processConnectRequest(
        ServerCnxn cnxn, ConnectRequest request) throws IOException, ClientCnxnLimitException {

    long sessionId = request.getSessionId(); // 默认0
    int tokensNeeded = 1;
    // 略

    // ro验证
    if (!request.getReadOnly() && this instanceof ReadOnlyZooKeeperServer) {
        String msg = "Refusing session request for not-read-only client";
        throw new CloseRequestException(msg, ServerCnxn.DisconnectReason.NOT_READ_ONLY_CLIENT);
    }
    // 客户端zxid验证
    if (request.getLastZxidSeen() > zkDb.dataTree.lastProcessedZxid) {
        String msg = "Refusing session request for client "
                     + cnxn.getRemoteSocketAddress()
                     + " as it has seen zxid 0x"
                     + Long.toHexString(request.getLastZxidSeen())
                     + " our last zxid is 0x"
                     + Long.toHexString(getZKDatabase().getDataTreeLastProcessedZxid())
                     + " client must try another server";
        throw new CloseRequestException(msg, ServerCnxn.DisconnectReason.CLIENT_ZXID_AHEAD);
    }
    int sessionTimeout = request.getTimeOut(); // 客户端默认30000
    byte[] passwd = request.getPasswd();
    int minSessionTimeout = getMinSessionTimeout(); // 默认tickTime * 2
    if (sessionTimeout < minSessionTimeout) {
        sessionTimeout = minSessionTimeout;
    }
    int maxSessionTimeout = getMaxSessionTimeout(); // 默认tickTime * 20
    if (sessionTimeout > maxSessionTimeout) {
        sessionTimeout = maxSessionTimeout;
    }
    cnxn.setSessionTimeout(sessionTimeout); // 设置超时时长

    // We don't want to receive any packets until we are sure that the session is setup
    cnxn.disableRecv();

    if (sessionId == 0) {
        // 创建新session
        long id = createSession(cnxn, passwd, sessionTimeout);
    } else {
        validateSession(cnxn, sessionId);
        // 杀掉旧的session和连接
        if (serverCnxnFactory != null) {
            serverCnxnFactory.closeSession(sessionId, ServerCnxn.DisconnectReason.CLIENT_RECONNECT);
        }
        if (secureServerCnxnFactory != null) {
            secureServerCnxnFactory.closeSession(sessionId, ServerCnxn.DisconnectReason.CLIENT_RECONNECT);
        }
        // add新session
        cnxn.setSessionId(sessionId);
        // 返回connect响应
        reopenSession(cnxn, sessionId, passwd, sessionTimeout);
        ServerMetrics.getMetrics().CONNECTION_REVALIDATE_COUNT.add(1);
    }
}

// 重点看一下创建新session
long createSession(ServerCnxn cnxn, byte[] passwd, int timeout) {
    if (passwd == null) {
        passwd = new byte[0];
    }
    long sessionId = sessionTracker.createSession(timeout); // 创建Session返回sessionId
    Random r = new Random(sessionId ^ superSecret);
    r.nextBytes(passwd); // passwd会赋值给request.passwd
    CreateSessionTxn txn = new CreateSessionTxn(timeout);
    cnxn.setSessionId(sessionId);
    // 给业务层处理器提交createSession请求
    // RequestRecord.fromRecord(txn)返回SimpleRequestRecord对象，封装Record对象
    Request si = new Request(cnxn, sessionId, 0, OpCode.createSession, RequestRecord.fromRecord(txn), null);
    submitRequest(si);
    return sessionId;
}

processPacket方法处理业务请求

ZooKeeperServer的processPacket方法用来处理业务请求：

public void processPacket(ServerCnxn cnxn, RequestHeader h, RequestRecord request) throws IOException {

    cnxn.incrOutstandingAndCheckThrottle(h);

    if (h.getType() == OpCode.auth) {
        // 略
        return;
    } else if (h.getType() == OpCode.sasl) {
        // 略
    } else {
        if (!authHelper.enforceAuthentication(cnxn, h.getXid())) {
            return;
        } else {
            Request si = new Request(
                cnxn, cnxn.getSessionId(), h.getXid(), h.getType(), request, cnxn.getAuthInfo());
            int length = request.limit();
            // 大请求验证
            if (isLargeRequest(length)) { // 默认返回false
                checkRequestSizeWhenMessageReceived(length);
                si.setLargeRequestSize(length);
            }
            si.setOwner(ServerCnxn.me);
            // 提交给业务层处理器
            submitRequest(si);
        }
    }
}

submitRequest流程

先把request提交给requestThrottler组件
requestThrottler是一个限流(默认不启用)组件，内部使用队列缓存request，异步线程消费队列，将request提交给业务处理器
直到submitRequest方法，业务处理才离开workerPool线程

if (request != null) {
    if (request.isStale()) {
        ServerMetrics.getMetrics().STALE_REQUESTS.add(1);
    }
    final long elapsedTime = Time.currentElapsedTime() - request.requestThrottleQueueTime;
    ServerMetrics.getMetrics().REQUEST_THROTTLE_QUEUE_TIME.add(elapsedTime);
    // 默认不限流
    if (shouldThrottleOp(request, elapsedTime)) {
      request.setIsThrottled(true);
      ServerMetrics.getMetrics().THROTTLED_OPS.add(1);
    }
    // 提交
    zks.submitRequestNow(request);
}

submitRequestNow方法将请求提交给业务层处理器：

public void submitRequestNow(Request si) {
    // 略
    try {
        touch(si.cnxn); // 刷新session过期时间
        boolean validpacket = Request.isValid(si.type);
        if (validpacket) {
            setLocalSessionFlag(si);
            firstProcessor.processRequest(si); // 提交给业务层处理器
            if (si.cnxn != null) {
                incInProcess();
            }
        } else {
            // Update request accounting/throttling limits
            requestFinished(si);
            new UnimplementedRequestProcessor().processRequest(si);
        }
    } catch (MissingSessionException e) {
        requestFinished(si);
    } catch (RequestProcessorException e) {
        requestFinished(si);
    }
}

Leader客户端业务层处理器链

在之前的文章已经介绍，leader使用LeaderZooKeeperServer作为服务实现类。

本章节介绍"leader处理客户端请求"的流程。

处理器链

// 构建处理器链
protected void setupRequestProcessors() {
    RequestProcessor finalProcessor = new FinalRequestProcessor(this);
    RequestProcessor toBeAppliedProcessor =
        new Leader.ToBeAppliedRequestProcessor(finalProcessor, getLeader());
    commitProcessor = new CommitProcessor(
        toBeAppliedProcessor, Long.toString(getServerId()), false, getZooKeeperServerListener());
    commitProcessor.start();
    ProposalRequestProcessor proposalProcessor = new ProposalRequestProcessor(this, commitProcessor);
    proposalProcessor.initialize();
    prepRequestProcessor = new PrepRequestProcessor(this, proposalProcessor);
    prepRequestProcessor.start();
    firstProcessor = new LeaderRequestProcessor(this, prepRequestProcessor);

    setupContainerManager();
}

FinalRequestProcessor - 处理与请求相关的事务，并提供查询服务，给客户端发响应，位于RequestProcessor链末尾
ToBeAppliedRequestProcessor - 维护toBeApplied列表，之后必须是FinalRequestProcessor且processRequest必须同步处理
CommitProcessor - 等待commit完成之后调用下游RequestProcessor处理器

ProposalRequestProcessor - 发起proposal并将Request转发给内部的SyncRequestProcessor和AckRequestProcessor

public ProposalRequestProcessor(LeaderZooKeeperServer zks, RequestProcessor nextProcessor) {
    this.zks = zks;
    this.nextProcessor = nextProcessor;
    // 内部有维护一个SyncRequestProcessor和AckRequestProcessor
    AckRequestProcessor ackProcessor = new AckRequestProcessor(zks.getLeader());
    syncProcessor = new SyncRequestProcessor(zks, ackProcessor);

    forwardLearnerRequestsToCommitProcessorDisabled = Boolean.getBoolean(
            FORWARD_LEARNER_REQUESTS_TO_COMMIT_PROCESSOR_DISABLED);
}

PrepRequestProcessor - 通常位于RequestProcessor链开头，为更新请求关联的事务做设置
LeaderRequestProcessor - 负责执行本地会话升级，只有直接提交给leader的Request才能通过这个处理器

LeaderRequestProcessor

public void processRequest(Request request) throws RequestProcessorException {
    // 略

    // 默认不支持localSession
    Request upgradeRequest = null;
    try {
        upgradeRequest = lzks.checkUpgradeSession(request);
    } catch (KeeperException ke) {
        // 略
    } catch (IOException ie) {
        // 略
    }
    // 此处upgradeRequest==null
    if (upgradeRequest != null) {
        nextProcessor.processRequest(upgradeRequest);
    }
    // 调用下游processor
    nextProcessor.processRequest(request);
}

PrepRequestProcessor

事务设置：

使用队列缓存request
消费线程从队列拉request设置事务

run方法

public void run() {
    try {
        while (true) {
            ServerMetrics.getMetrics().PREP_PROCESSOR_QUEUE_SIZE.add(submittedRequests.size());
            Request request = submittedRequests.take();
            ServerMetrics.getMetrics().PREP_PROCESSOR_QUEUE_TIME
                .add(Time.currentElapsedTime() - request.prepQueueStartTime);
            // 略
            if (Request.requestOfDeath == request) {
                break;
            }

            request.prepStartTime = Time.currentElapsedTime();
            pRequest(request);
        }
    } catch (Exception e) {
        handleException(this.getName(), e);
    }
}

protected void pRequest(Request request) throws RequestProcessorException {
    request.setHdr(null);
    request.setTxn(null);

    if (!request.isThrottled()) {
      pRequestHelper(request);
    }

    request.zxid = zks.getZxid(); // zxid
    long timeFinishedPrepare = Time.currentElapsedTime();
    ServerMetrics.getMetrics().PREP_PROCESS_TIME.add(timeFinishedPrepare - request.prepStartTime);
    nextProcessor.processRequest(request); // 调用下游processor
    ServerMetrics.getMetrics().PROPOSAL_PROCESS_TIME.add(Time.currentElapsedTime() - timeFinishedPrepare);
}

pRequestHelper方法

private void pRequestHelper(Request request) {
    try {
        switch (request.type) {
        case OpCode.createContainer:
        case OpCode.create:
        case OpCode.create2:
            // 创建节点请求封装path、data、acl、flag
            CreateRequest create2Request = request.readRequestRecord(CreateRequest::new);
            // zks.getNextZxid()获取递增zxid
            pRequest2Txn(request.type, zks.getNextZxid(), request, create2Request);
            break;
        case OpCode.createTTL:
            // 创建ttl请求封装path、data、acl、flag、ttl
            CreateTTLRequest createTtlRequest = request.readRequestRecord(CreateTTLRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, createTtlRequest);
            break;
        case OpCode.deleteContainer:
            // 封装path
            DeleteContainerRequest deleteContainerRequest =
                request.readRequestRecord(DeleteContainerRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, deleteContainerRequest);
            break;
        case OpCode.delete:
            // 删除节点请求封装path、version
            DeleteRequest deleteRequest = request.readRequestRecord(DeleteRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, deleteRequest);
            break;
        case OpCode.setData:
            // 设置节点数据请求封装path、data、version
            SetDataRequest setDataRequest = request.readRequestRecord(SetDataRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, setDataRequest);
            break;
        case OpCode.reconfig:
            // reconfig请求封装joiningServers、leavingServers、newMembers、curConfigId
            ReconfigRequest reconfigRequest = request.readRequestRecord(ReconfigRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, reconfigRequest);
            break;
        case OpCode.setACL:
            // 设置acl请求封装path、acl、version
            SetACLRequest setAclRequest = request.readRequestRecord(SetACLRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, setAclRequest);
            break;
        case OpCode.check:
            // check请求封装path、version
            CheckVersionRequest checkRequest = request.readRequestRecord(CheckVersionRequest::new);
            pRequest2Txn(request.type, zks.getNextZxid(), request, checkRequest);
            break;
        case OpCode.multi:
            // 遍历 逐个pRequest2Txn
            // pRequest2Txn(op.getType(), zxid, request, subrequest)
            // 封装MultiTxn
            break;

        // create/close session don't require request record
        case OpCode.createSession:
        case OpCode.closeSession:
            if (!request.isLocalSession()) { // 非本地会话
                pRequest2Txn(request.type, zks.getNextZxid(), request, null);
            }
            break;

        // All the rest don't need to create a Txn - just verify session
        case OpCode.sync:
        // sync,exists,getData,getACL,getChildren,getAllChildrenNumber,getChildren2,ping
        // setWatches,setWatches2,checkWatches,removeWatches,getEphemerals,multiRead,addWatch
        case OpCode.whoAmI:
            zks.sessionTracker.checkSession(request.sessionId, request.getOwner());
            break;
        default:
            break;
        }
    } catch (KeeperException e) {
        // 略
    } catch (Exception e) {
        // 略
    }
}

pRequest2Txn方法流程

代码量大，仅对重点的业务类型做简单分析。

该方法首先会为request设置TxnHeader信息：

if (request.getHdr() == null) {
    request.setHdr(new TxnHeader(request.sessionId, request.cxid, zxid, Time.currentWallTime(), type));
}

TxnHeader封装事务请求头：

public class TxnHeader implements Record {
  private long clientId; // 会话ID
  private int cxid; // 客户端xid
  private long zxid; // 服务端xid
  private long time;
  private int type; // 操作类型
}

pRequest2Txn - create相关操作

create/create2/createTTL/createContainer操作：

从flags创建createMode并验证ttl和ephemeral

验证acl

zks.checkACL(request.cnxn, parentRecord.acl, ZooDefs.Perms.CREATE, request.authInfo, path, listACL);

生成顺序节点path

int parentCVersion = parentRecord.stat.getCversion();
if (createMode.isSequential()) {
    // 形如/users/admin0000000001
    path = path + String.format(Locale.ENGLISH, "%010d", parentCVersion);
}
validatePath(path, request.sessionId);

request.setTxn

int newCversion = parentRecord.stat.getCversion() + 1;
if (type == OpCode.createContainer) {
    request.setTxn(new CreateContainerTxn(path, data, listACL, newCversion));
} else if (type == OpCode.createTTL) {
    request.setTxn(new CreateTTLTxn(path, data, listACL, newCversion, ttl));
} else {
    request.setTxn(new CreateTxn(path, data, listACL, createMode.isEphemeral(), newCversion));
}

获取ephemeralOwner

TxnHeader hdr = request.getHdr();
long ephemeralOwner = 0;
if (createMode.isContainer()) {
    ephemeralOwner = EphemeralType.CONTAINER_EPHEMERAL_OWNER;
} else if (createMode.isTTL()) {
    ephemeralOwner = EphemeralType.TTL.toEphemeralOwner(ttl);
} else if (createMode.isEphemeral()) {
    ephemeralOwner = request.sessionId;
}

addChangeRecord

StatPersisted s = DataTree.createStat(hdr.getZxid(), hdr.getTime(), ephemeralOwner);
parentRecord = parentRecord.duplicate(request.getHdr().getZxid());
parentRecord.childCount++;
parentRecord.stat.setCversion(newCversion);
parentRecord.stat.setPzxid(request.getHdr().getZxid());
parentRecord.precalculatedDigest = precalculateDigest(
        DigestOpCode.UPDATE, parentPath, parentRecord.data, parentRecord.stat);
addChangeRecord(parentRecord); // 维护outstandingChanges集
ChangeRecord nodeRecord = new ChangeRecord(request.getHdr().getZxid(), path, s, 0, listACL);
nodeRecord.data = data;
nodeRecord.precalculatedDigest = precalculateDigest(DigestOpCode.ADD, path, nodeRecord.data, s);
setTxnDigest(request, nodeRecord.precalculatedDigest);
addChangeRecord(nodeRecord); // 维护outstandingChanges集

pRequest2Txn - delete操作

验证acl和version

checkAndIncVersion(nodeRecord.stat.getVersion(), deleteRequest.getVersion(), path);

// stat.version与delete.version需要一致

验证没有子节点，有子节点无法删除
创建DeleteTxn
```
request.setTxn(new DeleteTxn(path));
```

addChangeRecord

parentRecord = parentRecord.duplicate(request.getHdr().getZxid());
parentRecord.childCount--;
parentRecord.stat.setPzxid(request.getHdr().getZxid());
parentRecord.precalculatedDigest = precalculateDigest(
        DigestOpCode.UPDATE, parentPath, parentRecord.data, parentRecord.stat);
addChangeRecord(parentRecord); // 维护outstandingChanges集

nodeRecord = new ChangeRecord(request.getHdr().getZxid(), path, null, -1, null);
nodeRecord.precalculatedDigest = precalculateDigest(DigestOpCode.REMOVE, path);
setTxnDigest(request, nodeRecord.precalculatedDigest);
addChangeRecord(nodeRecord); // 维护outstandingChanges集

pRequest2Txn - setData操作

验证acl、获取newVersion

创建SetDataTxn

request.setTxn(new SetDataTxn(path, setDataRequest.getData(), newVersion));

addChangeRecord

nodeRecord = nodeRecord.duplicate(request.getHdr().getZxid());
nodeRecord.stat.setVersion(newVersion);
nodeRecord.stat.setMtime(request.getHdr().getTime());
nodeRecord.stat.setMzxid(zxid);
nodeRecord.data = setDataRequest.getData();
nodeRecord.precalculatedDigest = precalculateDigest(
        DigestOpCode.UPDATE, path, nodeRecord.data, nodeRecord.stat);
setTxnDigest(request, nodeRecord.precalculatedDigest);
addChangeRecord(nodeRecord);

pRequest2Txn - setACL操作

验证acl、获取newVersion

创建SetACLTxn

request.setTxn(new SetACLTxn(path, listACL, newVersion));

addChangeRecord

pRequest2Txn - createSession操作

CreateSessionTxn createSessionTxn = request.readRequestRecord(CreateSessionTxn::new);
request.setTxn(createSessionTxn);
// only add the global session tracker but not to ZKDb
zks.sessionTracker.trackSession(request.sessionId, createSessionTxn.getTimeOut());
zks.setOwner(request.sessionId, request.getOwner());

pRequest2Txn - closeSession操作

long startTime = Time.currentElapsedTime();
synchronized (zks.outstandingChanges) {
    // 获取所有临时节点
    Set es = zks.getZKDatabase().getEphemerals(request.sessionId);
    for (ChangeRecord c : zks.outstandingChanges) {
        if (c.stat == null) {
            // Doing a delete
            es.remove(c.path);
        } else if (c.stat.getEphemeralOwner() == request.sessionId) {
            es.add(c.path);
        }
    }
    for (String path2Delete : es) {
        if (digestEnabled) {
            parentPath = getParentPathAndValidate(path2Delete);
            parentRecord = getRecordForPath(parentPath);
            parentRecord = parentRecord.duplicate(request.getHdr().getZxid());
            parentRecord.stat.setPzxid(request.getHdr().getZxid());
            parentRecord.precalculatedDigest = precalculateDigest(
                    DigestOpCode.UPDATE, parentPath, parentRecord.data, parentRecord.stat);
            addChangeRecord(parentRecord);
        }
        nodeRecord = new ChangeRecord(request.getHdr().getZxid(), path2Delete, null, 0, null);
        nodeRecord.precalculatedDigest = precalculateDigest(DigestOpCode.REMOVE, path2Delete);
        addChangeRecord(nodeRecord);
    }
    if (ZooKeeperServer.isCloseSessionTxnEnabled()) {
        request.setTxn(new CloseSessionTxn(new ArrayList(es)));
    }
    zks.sessionTracker.setSessionClosing(request.sessionId);
}

ProposalRequestProcessor

processRequest方法

public void processRequest(Request request) throws RequestProcessorException {
    if (request instanceof LearnerSyncRequest) { // 处理sync命令，后续补充sync命令分析
        zks.getLeader().processSync((LearnerSyncRequest) request);
    } else {
        if (shouldForwardToNextProcessor(request)) {
            nextProcessor.processRequest(request); // 调用下游processor(CommitProcessor)
        }
        if (request.getHdr() != null) { // 事务消息需要发proposal、写磁盘
            // We need to sync and get consensus on any transactions
            try {
                zks.getLeader().propose(request); // 给follower发proposal
            } catch (XidRolloverException e) {
                throw new RequestProcessorException(e.getMessage(), e);
            }
            // 该对象的nextProcessor是AckRequestProcessor
            syncProcessor.processRequest(request);
        }
    }
}

发proposal

发起一个proposal并发给所有成员：

public Proposal propose(Request request) throws XidRolloverException {
    // zxid的低32位满了，强制重新选举，生成新一轮epoch和zxid
    if ((request.zxid & 0xffffffffL) == 0xffffffffL) {
        String msg =
            "zxid lower 32 bits have rolled over, forcing re-election, and therefore new epoch start";
        shutdown(msg);
        throw new XidRolloverException(msg);
    }

    // 序列化
    byte[] data = request.getSerializeData();
    proposalStats.setLastBufferSize(data.length);
    // 封装数据包
    QuorumPacket pp = new QuorumPacket(Leader.PROPOSAL, request.zxid, data, null);

    // 封装Proposal对象
    Proposal p = new Proposal();
    p.packet = pp;
    p.request = request;

    synchronized (this) {
        p.addQuorumVerifier(self.getQuorumVerifier());

        if (request.getHdr().getType() == OpCode.reconfig) {
            // 此处会把lastSeenQuorumVerifier写入zoo.cfg.dynamic.next文件
            self.setLastSeenQuorumVerifier(request.qv, true);
        }

        if (self.getQuorumVerifier().getVersion() < self.getLastSeenQuorumVerifier().getVersion()) {
            p.addQuorumVerifier(self.getLastSeenQuorumVerifier());
        }

        lastProposed = p.packet.getZxid();
        // 缓存到outstandingProposals中，processAck时会根据quorum状态确定是否提交
        outstandingProposals.put(lastProposed, p);
        // 给follower发数据
        sendPacket(pp);
    }
    ServerMetrics.getMetrics().PROPOSAL_COUNT.add(1);
    return p;
}

syncProcessor.processRequest方法

processRequest方法将request放入queuedRequests队列，异步线程消费做业务处理：

从queuedRequests拉request
写txnlog
```
zks.getZKDatabase().append(si);
```

滚动txnlog文件、生成snapshot文件

// 默认当logCount超过了50000或logSize超过2GB时触发
if (shouldSnapshot()) {
    resetSnapshotStats();
    // 滚动txnlog文件
    zks.getZKDatabase().rollLog();
    // 生成snapshot文件
    if (!snapThreadMutex.tryAcquire()) {
        LOG.warn("Too busy to snap, skipping");
    } else {
        // 异步线程生成snapshot文件
        new ZooKeeperThread("Snapshot Thread") {
            public void run() {
                try {
                    zks.takeSnapshot();
                } catch (Exception e) {
                } finally {
                    snapThreadMutex.release();
                }
            }
        }.start();
    }
}

之后会把request传递给nextProcessor(AckRequestProcessor对象)

AckRequestProcessor

public void processRequest(Request request) {
    QuorumPeer self = leader.self;
    if (self != null) {
        request.logLatency(ServerMetrics.getMetrics().PROPOSAL_ACK_CREATION_LATENCY);
        leader.processAck(self.getMyId(), request.zxid, null);
    }
}

processAck

Keep a count of acks that are received by the leader for a particular proposal.

public synchronized void processAck(long sid, long zxid, SocketAddress followerAddr) {

    // 略

    if ((zxid & 0xffffffffL) == 0) {
        // We no longer process NEWLEADER ack with this method. However,
        // the learner sends an ack back to the leader after it gets
        // UPTODATE, so we just ignore the message.
        return;
    }

    if (outstandingProposals.size() == 0) {
        return;
    }
    // 说明zxid的数据已经提交
    if (lastCommitted >= zxid) {
        // The proposal has already been committed
        return;
    }
    Proposal p = outstandingProposals.get(zxid);
    if (p == null) {
        return;
    }

    // 略

    p.addAck(sid); // 添加ack

    boolean hasCommitted = tryToCommit(p, zxid, followerAddr);

    // reconfig类型命令的特殊处理，略
}

tryToCommit方法会判断quorum状态，即超过半数ack，如果到了quorum状态：

从outstandingProposals集移除
加入到toBeApplied集

给follower发COMMIT

public void commit(long zxid) {
    synchronized (this) {
        lastCommitted = zxid;
    }
    QuorumPacket qp = new QuorumPacket(Leader.COMMIT, zxid, null, null);
    sendPacket(qp); // 发给follower
}

提交

zk.commitProcessor.commit(p.request);

// 会进入commitProcessor的committedRequests队列

CommitProcessor

processRequest方法

本地写磁盘之后即调用此方法：

把request提交到queuedRequests队列
写请求提交到queuedWriteRequests队列

public void processRequest(Request request) {
    request.commitProcQueueStartTime = Time.currentElapsedTime();
    queuedRequests.add(request); // 所有请求
    // If the request will block, add it to the queue of blocking requests
    if (needCommit(request)) { // 写请求
        queuedWriteRequests.add(request);
        numWriteQueuedRequests.incrementAndGet();
    } else {
        numReadQueuedRequests.incrementAndGet();
    }
    wakeup();
}

commit方法

follower对proposal到了quorum状态后，会使用这个方法提交事务，然后会将事务写到ZKDatabase中。

public void commit(Request request) {
    request.commitRecvTime = Time.currentElapsedTime();
    ServerMetrics.getMetrics().COMMITS_QUEUED.add(1);
    committedRequests.add(request); // 进committedRequests队列
    wakeup();
}

run方法

对比queuedRequests、queuedWriteRequests、committedRequests这几个队列，将提交成功的请求或读请求转发给下游的ToBeAppliedRequestProcessor处理器。

ToBeAppliedRequestProcessor

维护toBeApplied列表：清理已提交成功的request数据。

FinalRequestProcessor

处理与请求相关的事务，并提供查询服务，给客户端发响应，位于RequestProcessor链末尾。

执行事务
区分OpCode执行对应逻辑，发回响应
使用cnxn把响应返回给客户端

执行事务

if (!request.isThrottled()) {
  rc = applyRequest(request);
}

// ProcessTxnResult rc = zks.processTxn(request);

createSession操作

zks.finishSessionInit(request.cnxn, true);

closeSession操作

给客户端发closeConn数据包：

cnxn.sendCloseSession();

create相关操作

create、create2、createTTL、createContainer操作，创建对应的Response对象。

delete相关操作

略。

setData操作

返回SetDataResponse响应。

setACL操作

返回SetACLResponse响应。

getData操作

private Record handleGetDataRequest(
        Record request, ServerCnxn cnxn, List authInfo) throws KeeperException, IOException {
    GetDataRequest getDataRequest = (GetDataRequest) request;
    String path = getDataRequest.getPath();
    DataNode n = zks.getZKDatabase().getNode(path);
    if (n == null) {
        throw new KeeperException.NoNodeException();
    }
    // 检查权限
    zks.checkACL(cnxn, zks.getZKDatabase().aclForNode(n), ZooDefs.Perms.READ, authInfo, path, null);
    Stat stat = new Stat();
    // 查询数据、addWatcher
    byte[] b = zks.getZKDatabase().getData(path, stat, getDataRequest.getWatch() ? cnxn : null);
    return new GetDataResponse(b, stat);
}

setWatches相关操作

setWatches、setWatches2操作：

SetWatches2 setWatches = request.readRequestRecord(SetWatches2::new);
long relativeZxid = setWatches.getRelativeZxid();
zks.getZKDatabase().setWatches(relativeZxid,
        setWatches.getDataWatches(),
        setWatches.getExistWatches(),
        setWatches.getChildWatches(),
        setWatches.getPersistentWatches(),
        setWatches.getPersistentRecursiveWatches(),
        cnxn);

addWatch操作

AddWatchRequest addWatcherRequest = request.readRequestRecord(AddWatchRequest::new);
zks.getZKDatabase().addWatch(addWatcherRequest.getPath(), cnxn, addWatcherRequest.getMode());

removeWatches操作

RemoveWatchesRequest removeWatches = request.readRequestRecord(RemoveWatchesRequest::new);
WatcherType type = WatcherType.fromInt(removeWatches.getType());
path = removeWatches.getPath();
boolean removed = zks.getZKDatabase().removeWatch(path, type, cnxn);

getChildren相关操作

getChildren、getChildren2操作：

GetChildren2Request getChildren2Request = request.readRequestRecord(GetChildren2Request::new);
Stat stat = new Stat();
path = getChildren2Request.getPath();
DataNode n = zks.getZKDatabase().getNode(path);

zks.checkACL(request.cnxn, zks.getZKDatabase().aclForNode(n),
             ZooDefs.Perms.READ, request.authInfo, path, null);
List children = zks.getZKDatabase()
                           .getChildren(path, stat, getChildren2Request.getWatch() ? cnxn : null);
rsp = new GetChildren2Response(children, stat);

Follower处理Leader数据

处理器链

protected void setupRequestProcessors() {
    RequestProcessor finalProcessor = new FinalRequestProcessor(this);
    commitProcessor = new CommitProcessor(
        finalProcessor, Long.toString(getServerId()), true, getZooKeeperServerListener());
    commitProcessor.start();
    firstProcessor = new FollowerRequestProcessor(this, commitProcessor);
    ((FollowerRequestProcessor) firstProcessor).start();

    syncProcessor = new SyncRequestProcessor(this, new SendAckRequestProcessor(getFollower()));
    syncProcessor.start();
}

处理器链：

FollowerRequestProcessor -> CommitProcessor -> FinalRequestProcessor

commitProcessor和syncProcessor处理leader的proposal和commit请求。

processPacket方法

在"zookeeper源码(08)leader、follower和observer"中已经介绍，Follower使用processPacket方法处理来自leader的数据包：

protected void processPacket(QuorumPacket qp) throws Exception {
    switch (qp.getType()) {
    case Leader.PING:
        ping(qp);
        break;
    case Leader.PROPOSAL: // 提案
        ServerMetrics.getMetrics().LEARNER_PROPOSAL_RECEIVED_COUNT.add(1);
        TxnLogEntry logEntry = SerializeUtils.deserializeTxn(qp.getData());
        TxnHeader hdr = logEntry.getHeader();
        Record txn = logEntry.getTxn();
        TxnDigest digest = logEntry.getDigest();
        // 略
        lastQueued = hdr.getZxid();

        // 略

        // 记录log数据
        // 使用syncProcessor持久化log数据，之后给leader发ack
        fzk.logRequest(hdr, txn, digest);
        // 略
        if (om != null) {
            // 略
        }
        break;
    case Leader.COMMIT: // 提交
        ServerMetrics.getMetrics().LEARNER_COMMIT_RECEIVED_COUNT.add(1);
        fzk.commit(qp.getZxid()); // 使用commitProcessor提交log
        if (om != null) {
            // 略
        }
        break;
    case Leader.COMMITANDACTIVATE: // Similar to COMMIT, only for a reconfig operation
        // get the new configuration from the request
        Request request = fzk.pendingTxns.element();
        SetDataTxn setDataTxn = (SetDataTxn) request.getTxn();
        QuorumVerifier qv = self.configFromString(new String(setDataTxn.getData(), UTF_8));

        // get new designated leader from (current) leader's message
        ByteBuffer buffer = ByteBuffer.wrap(qp.getData());
        long suggestedLeaderId = buffer.getLong();
        final long zxid = qp.getZxid();
        boolean majorChange = self.processReconfig(qv, suggestedLeaderId, zxid, true);
        // commit (writes the new config to ZK tree (/zookeeper/config)
        fzk.commit(zxid);

        // 略
        break;
    case Leader.UPTODATE:
        // leader告知follower已处于最新状态，可以开始响应客户端
        // 正常情况下不应该再出现该类型请求
        break;
    case Leader.REVALIDATE:
        if (om == null || !om.revalidateLearnerSession(qp)) {
            revalidate(qp);
        }
        break;
    case Leader.SYNC:
        fzk.sync(); // sync命令
        break;
    default:
        LOG.warn("Unknown packet type");
        break;
    }
}

处理PROPOSAL

syncProcessor.processRequest方法

processRequest方法将request放入queuedRequests队列，异步线程消费做业务处理。

在本地持久化之后，调用下游处理器(SendAckRequestProcessor对象)。

SendAckRequestProcessor

public void processRequest(Request si) {
    if (si.type != OpCode.sync) {
        // 确认zxid已持久化
        QuorumPacket qp = new QuorumPacket(Leader.ACK, si.getHdr().getZxid(), null, null);
        try {
            si.logLatency(ServerMetrics.getMetrics().PROPOSAL_ACK_CREATION_LATENCY);
            learner.writePacket(qp, false);
        } catch (IOException e) {
            // learner.sock.close();
        }
    }
}

public void flush() throws IOException {
    try {
        learner.writePacket(null, true);
    } catch (IOException e) {
        // learner.sock.close();
    }
}

处理COMMIT

提交给commitProcessor处理器，该处理器会继续向下游(FinalRequestProcessor)传递。

FinalRequestProcessor

上文已经介绍，此处省略。

Observer处理Leader数据

处理器链

protected void setupRequestProcessors() {
    // We might consider changing the processor behaviour of
    // Observers to, for example, remove the disk sync requirements.
    // Currently, they behave almost exactly the same as followers.
    RequestProcessor finalProcessor = new FinalRequestProcessor(this);
    commitProcessor = new CommitProcessor(
        finalProcessor, Long.toString(getServerId()), true, getZooKeeperServerListener());
    commitProcessor.start();
    firstProcessor = new ObserverRequestProcessor(this, commitProcessor);
    ((ObserverRequestProcessor) firstProcessor).start();

    if (syncRequestProcessorEnabled) {
        syncProcessor = new SyncRequestProcessor(this, null);
        syncProcessor.start();
    }
}

processPacket方法

protected void processPacket(QuorumPacket qp) throws Exception {
    TxnLogEntry logEntry;
    TxnHeader hdr;
    TxnDigest digest;
    Record txn;
    switch (qp.getType()) {
    case Leader.PING:
        ping(qp);
        break;
    case Leader.PROPOSAL:
        LOG.warn("Ignoring proposal");
        break;
    case Leader.COMMIT:
        LOG.warn("Ignoring commit");
        break;
    case Leader.UPTODATE:
        LOG.error("Received an UPTODATE message after Observer started");
        break;
    case Leader.REVALIDATE:
        revalidate(qp);
        break;
    case Leader.SYNC:
        ((ObserverZooKeeperServer) zk).sync();
        break;
    case Leader.INFORM:
        ServerMetrics.getMetrics().LEARNER_COMMIT_RECEIVED_COUNT.add(1);
        logEntry = SerializeUtils.deserializeTxn(qp.getData());
        hdr = logEntry.getHeader();
        txn = logEntry.getTxn();
        digest = logEntry.getDigest();
        Request request = new Request(hdr.getClientId(), hdr.getCxid(), hdr.getType(), hdr, txn, 0);
        request.logLatency(ServerMetrics.getMetrics().COMMIT_PROPAGATION_LATENCY);
        request.setTxnDigest(digest);
        ObserverZooKeeperServer obs = (ObserverZooKeeperServer) zk;
        obs.commitRequest(request);
        break;
    case Leader.INFORMANDACTIVATE: // 处理reconfig请求
        // get new designated leader from (current) leader's message
        ByteBuffer buffer = ByteBuffer.wrap(qp.getData());
        long suggestedLeaderId = buffer.getLong();

        byte[] remainingdata = new byte[buffer.remaining()];
        buffer.get(remainingdata);
        logEntry = SerializeUtils.deserializeTxn(remainingdata);
        hdr = logEntry.getHeader();
        txn = logEntry.getTxn();
        digest = logEntry.getDigest();
        QuorumVerifier qv = self.configFromString(new String(((SetDataTxn) txn).getData(), UTF_8));

        request = new Request(hdr.getClientId(), hdr.getCxid(), hdr.getType(), hdr, txn, 0);
        request.setTxnDigest(digest);
        obs = (ObserverZooKeeperServer) zk;

        boolean majorChange = self.processReconfig(qv, suggestedLeaderId, qp.getZxid(), true);

        obs.commitRequest(request);

        if (majorChange) {
            throw new Exception("changes proposed in reconfig");
        }
        break;
    default:
        LOG.warn("Unknown packet type: {}", LearnerHandler.packetToString(qp));
        break;
    }
}

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原文地址：https://www.cnblogs.com/xugf/p/18020590