上文：
zookeeper源码分析之一服务端启动过程
中，我们介绍了zookeeper服务器的启动过程，其中单机是ZookeeperServer启动，集群使用QuorumPeer启动，那么这次我们分析各自一下消息处理过程：
前文可以看到在
1.在单机情况下NettyServerCnxnFactory中启动ZookeeperServer来处理消息：
public synchronized void startup() { if (sessionTracker == null) { createSessionTracker(); } startSessionTracker(); setupRequestProcessors(); registerJMX(); state = State.RUNNING; notifyAll(); }
消息处理器的调用如下：
protected void setupRequestProcessors() { RequestProcessor finalProcessor = new FinalRequestProcessor(this); RequestProcessor syncProcessor = new SyncRequestProcessor(this, finalProcessor); ((SyncRequestProcessor)syncProcessor).start(); firstProcessor = new PrepRequestProcessor(this, syncProcessor); ((PrepRequestProcessor)firstProcessor).start(); }
我们看到启动两个消息处理器来处理请求：第一个同步消息处理器预消息服务器，最后一个同步请求处理器和异步请求处理器。
1.1 第一个消息服务器处理器预消息服务器PrepRequestProcessor
@Override public void run() { try { while (true) { Request request = submittedRequests.take(); long traceMask = ZooTrace.CLIENT_REQUEST_TRACE_MASK; if (request.type == OpCode.ping) { traceMask = ZooTrace.CLIENT_PING_TRACE_MASK; } if (LOG.isTraceEnabled()) { ZooTrace.logRequest(LOG, traceMask, 'P', request, ""); } if (Request.requestOfDeath == request) { break; } pRequest(request); } } catch (RequestProcessorException e) { if (e.getCause() instanceof XidRolloverException) { LOG.info(e.getCause().getMessage()); } handleException(this.getName(), e); } catch (Exception e) { handleException(this.getName(), e); } LOG.info("PrepRequestProcessor exited loop!"); }
可以看到，while(true)是一个一直循环处理的过程，其中红色的部分为处理的主体。
/** * This method will be called inside the ProcessRequestThread, which is a * singleton, so there will be a single thread calling this code. * * @param request */ protected void pRequest(Request request) throws RequestProcessorException { // LOG.info("Prep>>> cxid = " + request.cxid + " type = " + // request.type + " id = 0x" + Long.toHexString(request.sessionId)); request.setHdr(null); request.setTxn(null); try { switch (request.type) { case OpCode.createContainer: case OpCode.create: case OpCode.create2: CreateRequest create2Request = new CreateRequest(); pRequest2Txn(request.type, zks.getNextZxid(), request, create2Request, true); break; case OpCode.deleteContainer: case OpCode.delete: DeleteRequest deleteRequest = new DeleteRequest(); pRequest2Txn(request.type, zks.getNextZxid(), request, deleteRequest, true); break; case OpCode.setData: SetDataRequest setDataRequest = new SetDataRequest(); pRequest2Txn(request.type, zks.getNextZxid(), request, setDataRequest, true); break; case OpCode.reconfig: ReconfigRequest reconfigRequest = new ReconfigRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, reconfigRequest); pRequest2Txn(request.type, zks.getNextZxid(), request, reconfigRequest, true); break; case OpCode.setACL: SetACLRequest setAclRequest = new SetACLRequest(); pRequest2Txn(request.type, zks.getNextZxid(), request, setAclRequest, true); break; case OpCode.check: CheckVersionRequest checkRequest = new CheckVersionRequest(); pRequest2Txn(request.type, zks.getNextZxid(), request, checkRequest, true); break; case OpCode.multi: MultiTransactionRecord multiRequest = new MultiTransactionRecord(); try { ByteBufferInputStream.byteBuffer2Record(request.request, multiRequest); } catch(IOException e) { request.setHdr(new TxnHeader(request.sessionId, request.cxid, zks.getNextZxid(), Time.currentWallTime(), OpCode.multi)); throw e; } List<Txn> txns = new ArrayList<Txn>(); //Each op in a multi-op must have the same zxid! long zxid = zks.getNextZxid(); KeeperException ke = null; //Store off current pending change records in case we need to rollback Map<String, ChangeRecord> pendingChanges = getPendingChanges(multiRequest); for(Op op: multiRequest) { Record subrequest = op.toRequestRecord(); int type; Record txn; /* If we've already failed one of the ops, don't bother * trying the rest as we know it's going to fail and it * would be confusing in the logfiles. */ if (ke != null) { type = OpCode.error; txn = new ErrorTxn(Code.RUNTIMEINCONSISTENCY.intValue()); } /* Prep the request and convert to a Txn */ else { try { pRequest2Txn(op.getType(), zxid, request, subrequest, false); type = request.getHdr().getType(); txn = request.getTxn(); } catch (KeeperException e) { ke = e; type = OpCode.error; txn = new ErrorTxn(e.code().intValue()); LOG.info("Got user-level KeeperException when processing " + request.toString() + " aborting remaining multi ops." + " Error Path:" + e.getPath() + " Error:" + e.getMessage()); request.setException(e); /* Rollback change records from failed multi-op */ rollbackPendingChanges(zxid, pendingChanges); } } //FIXME: I don't want to have to serialize it here and then // immediately deserialize in next processor. But I'm // not sure how else to get the txn stored into our list. ByteArrayOutputStream baos = new ByteArrayOutputStream(); BinaryOutputArchive boa = BinaryOutputArchive.getArchive(baos); txn.serialize(boa, "request") ; ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray()); txns.add(new Txn(type, bb.array())); } request.setHdr(new TxnHeader(request.sessionId, request.cxid, zxid, Time.currentWallTime(), request.type)); request.setTxn(new MultiTxn(txns)); break; //create/close session don't require request record case OpCode.createSession: case OpCode.closeSession: if (!request.isLocalSession()) { pRequest2Txn(request.type, zks.getNextZxid(), request, null, true); } break; //All the rest don't need to create a Txn - just verify session case OpCode.sync: case OpCode.exists: case OpCode.getData: case OpCode.getACL: case OpCode.getChildren: case OpCode.getChildren2: case OpCode.ping: case OpCode.setWatches: case OpCode.checkWatches: case OpCode.removeWatches: zks.sessionTracker.checkSession(request.sessionId, request.getOwner()); break; default: LOG.warn("unknown type " + request.type); break; } } catch (KeeperException e) { if (request.getHdr() != null) { request.getHdr().setType(OpCode.error); request.setTxn(new ErrorTxn(e.code().intValue())); } LOG.info("Got user-level KeeperException when processing " + request.toString() + " Error Path:" + e.getPath() + " Error:" + e.getMessage()); request.setException(e); } catch (Exception e) { // log at error level as we are returning a marshalling // error to the user LOG.error("Failed to process " + request, e); StringBuilder sb = new StringBuilder(); ByteBuffer bb = request.request; if(bb != null){ bb.rewind(); while (bb.hasRemaining()) { sb.append(Integer.toHexString(bb.get() & 0xff)); } } else { sb.append("request buffer is null"); } LOG.error("Dumping request buffer: 0x" + sb.toString()); if (request.getHdr() != null) { request.getHdr().setType(OpCode.error); request.setTxn(new ErrorTxn(Code.MARSHALLINGERROR.intValue())); } } request.zxid = zks.getZxid(); nextProcessor.processRequest(request); }
排除异常的逻辑，该方法是处理不同类型的request，根据type选择一个处理分支，ProcessRequestThread内部调用该方法，它是单例的，因此只有一个单线程调用此代码。以create请求为例(红色部分)，了解工作机制：
CreateRequest createRequest = (CreateRequest)record; if (deserialize) { ByteBufferInputStream.byteBuffer2Record(request.request, createRequest); } CreateMode createMode = CreateMode.fromFlag(createRequest.getFlags()); validateCreateRequest(createMode, request); String path = createRequest.getPath(); String parentPath = validatePathForCreate(path, request.sessionId); List<ACL> listACL = fixupACL(path, request.authInfo, createRequest.getAcl()); ChangeRecord parentRecord = getRecordForPath(parentPath); checkACL(zks, parentRecord.acl, ZooDefs.Perms.CREATE, request.authInfo); int parentCVersion = parentRecord.stat.getCversion(); if (createMode.isSequential()) { path = path + String.format(Locale.ENGLISH, "%010d", parentCVersion); } validatePath(path, request.sessionId); try { if (getRecordForPath(path) != null) { throw new KeeperException.NodeExistsException(path); } } catch (KeeperException.NoNodeException e) { // ignore this one } boolean ephemeralParent = (parentRecord.stat.getEphemeralOwner() != 0) && (parentRecord.stat.getEphemeralOwner() != DataTree.CONTAINER_EPHEMERAL_OWNER); if (ephemeralParent) { throw new KeeperException.NoChildrenForEphemeralsException(path); } int newCversion = parentRecord.stat.getCversion()+1; if (type == OpCode.createContainer) { request.setTxn(new CreateContainerTxn(path, createRequest.getData(), listACL, newCversion)); } else { request.setTxn(new CreateTxn(path, createRequest.getData(), listACL, createMode.isEphemeral(), newCversion)); } StatPersisted s = new StatPersisted(); if (createMode.isEphemeral()) { s.setEphemeralOwner(request.sessionId); } parentRecord = parentRecord.duplicate(request.getHdr().getZxid()); parentRecord.childCount++; parentRecord.stat.setCversion(newCversion); addChangeRecord(parentRecord); addChangeRecord(new ChangeRecord(request.getHdr().getZxid(), path, s, 0, listACL)); break;
调用方法，处理变化：
private void addChangeRecord(ChangeRecord c) { synchronized (zks.outstandingChanges) { zks.outstandingChanges.add(c); zks.outstandingChangesForPath.put(c.path, c); } }
继续向下
private void addChangeRecord(ChangeRecord c) { synchronized (zks.outstandingChanges) { zks.outstandingChanges.add(c); zks.outstandingChangesForPath.put(c.path, c); } }
其中：outstandingChanges 是一组ChangeRecord，outstandingChangesForPath是map的ChangeRecord，如下定义：
final List<ChangeRecord> outstandingChanges = new ArrayList<ChangeRecord>();
// this data structure must be accessed under the outstandingChanges lock
final HashMap<String, ChangeRecord> outstandingChangesForPath =
new HashMap<String, ChangeRecord>();
ChangeRecord是一个数据结构，方便PrepRP和FinalRp共享信息。
ChangeRecord(long zxid, String path, StatPersisted stat, int childCount, List<ACL> acl) { this.zxid = zxid; this.path = path; this.stat = stat; this.childCount = childCount; this.acl = acl; }
1.2 先看一下同步请求处理器FinalRequestProcessor，这个请求处理器实际上应用到一个请求的所有事务，针对任何查询提供服务。它通常处于请求处理的最后（不会有下一个消息处理器），故此得名。 它是如何处理请求呢？
public void processRequest(Request request) { if (LOG.isDebugEnabled()) { LOG.debug("Processing request:: " + request); } // request.addRQRec(">final"); long traceMask = ZooTrace.CLIENT_REQUEST_TRACE_MASK; if (request.type == OpCode.ping) { traceMask = ZooTrace.SERVER_PING_TRACE_MASK; } if (LOG.isTraceEnabled()) { ZooTrace.logRequest(LOG, traceMask, 'E', request, ""); } ProcessTxnResult rc = null; synchronized (zks.outstandingChanges) { // Need to process local session requests rc = zks.processTxn(request); // request.hdr is set for write requests, which are the only ones // that add to outstandingChanges. if (request.getHdr() != null) { TxnHeader hdr = request.getHdr(); Record txn = request.getTxn(); long zxid = hdr.getZxid(); while (!zks.outstandingChanges.isEmpty() && zks.outstandingChanges.get(0).zxid <= zxid) { ChangeRecord cr = zks.outstandingChanges.remove(0); if (cr.zxid < zxid) { LOG.warn("Zxid outstanding " + cr.zxid + " is less than current " + zxid); } if (zks.outstandingChangesForPath.get(cr.path) == cr) { zks.outstandingChangesForPath.remove(cr.path); } } } // do not add non quorum packets to the queue. if (request.isQuorum()) { zks.getZKDatabase().addCommittedProposal(request); } } // ZOOKEEPER-558: // In some cases the server does not close the connection (e.g., closeconn buffer // was not being queued — ZOOKEEPER-558) properly. This happens, for example, // when the client closes the connection. The server should still close the session, though. // Calling closeSession() after losing the cnxn, results in the client close session response being dropped. if (request.type == OpCode.closeSession && connClosedByClient(request)) { // We need to check if we can close the session id. // Sometimes the corresponding ServerCnxnFactory could be null because // we are just playing diffs from the leader. if (closeSession(zks.serverCnxnFactory, request.sessionId) || closeSession(zks.secureServerCnxnFactory, request.sessionId)) { return; } } if (request.cnxn == null) { return; } ServerCnxn cnxn = request.cnxn; String lastOp = "NA"; zks.decInProcess(); Code err = Code.OK; Record rsp = null; try { if (request.getHdr() != null && request.getHdr().getType() == OpCode.error) { /* * When local session upgrading is disabled, leader will * reject the ephemeral node creation due to session expire. * However, if this is the follower that issue the request, * it will have the correct error code, so we should use that * and report to user */ if (request.getException() != null) { throw request.getException(); } else { throw KeeperException.create(KeeperException.Code .get(((ErrorTxn) request.getTxn()).getErr())); } } KeeperException ke = request.getException(); if (ke != null && request.type != OpCode.multi) { throw ke; } if (LOG.isDebugEnabled()) { LOG.debug("{}",request); } switch (request.type) { case OpCode.ping: { zks.serverStats().updateLatency(request.createTime); lastOp = "PING"; cnxn.updateStatsForResponse(request.cxid, request.zxid, lastOp, request.createTime, Time.currentElapsedTime()); cnxn.sendResponse(new ReplyHeader(-2, zks.getZKDatabase().getDataTreeLastProcessedZxid(), 0), null, "response"); return; } case OpCode.createSession: { zks.serverStats().updateLatency(request.createTime); lastOp = "SESS"; cnxn.updateStatsForResponse(request.cxid, request.zxid, lastOp, request.createTime, Time.currentElapsedTime()); zks.finishSessionInit(request.cnxn, true); return; } case OpCode.multi: { lastOp = "MULT"; rsp = new MultiResponse() ; for (ProcessTxnResult subTxnResult : rc.multiResult) { OpResult subResult ; switch (subTxnResult.type) { case OpCode.check: subResult = new CheckResult(); break; case OpCode.create: subResult = new CreateResult(subTxnResult.path); break; case OpCode.create2: case OpCode.createContainer: subResult = new CreateResult(subTxnResult.path, subTxnResult.stat); break; case OpCode.delete: case OpCode.deleteContainer: subResult = new DeleteResult(); break; case OpCode.setData: subResult = new SetDataResult(subTxnResult.stat); break; case OpCode.error: subResult = new ErrorResult(subTxnResult.err) ; break; default: throw new IOException("Invalid type of op"); } ((MultiResponse)rsp).add(subResult); } break; } case OpCode.create: { lastOp = "CREA"; rsp = new CreateResponse(rc.path); err = Code.get(rc.err); break; } case OpCode.create2: case OpCode.createContainer: { lastOp = "CREA"; rsp = new Create2Response(rc.path, rc.stat); err = Code.get(rc.err); break; } case OpCode.delete: case OpCode.deleteContainer: { lastOp = "DELE"; err = Code.get(rc.err); break; } case OpCode.setData: { lastOp = "SETD"; rsp = new SetDataResponse(rc.stat); err = Code.get(rc.err); break; } case OpCode.reconfig: { lastOp = "RECO"; rsp = new GetDataResponse(((QuorumZooKeeperServer)zks).self.getQuorumVerifier().toString().getBytes(), rc.stat); err = Code.get(rc.err); break; } case OpCode.setACL: { lastOp = "SETA"; rsp = new SetACLResponse(rc.stat); err = Code.get(rc.err); break; } case OpCode.closeSession: { lastOp = "CLOS"; err = Code.get(rc.err); break; } case OpCode.sync: { lastOp = "SYNC"; SyncRequest syncRequest = new SyncRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, syncRequest); rsp = new SyncResponse(syncRequest.getPath()); break; } case OpCode.check: { lastOp = "CHEC"; rsp = new SetDataResponse(rc.stat); err = Code.get(rc.err); break; } case OpCode.exists: { lastOp = "EXIS"; // TODO we need to figure out the security requirement for this! ExistsRequest existsRequest = new ExistsRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, existsRequest); String path = existsRequest.getPath(); if (path.indexOf('\0') != -1) { throw new KeeperException.BadArgumentsException(); } Stat stat = zks.getZKDatabase().statNode(path, existsRequest .getWatch() ? cnxn : null); rsp = new ExistsResponse(stat); break; } case OpCode.getData: { lastOp = "GETD"; GetDataRequest getDataRequest = new GetDataRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, getDataRequest); DataNode n = zks.getZKDatabase().getNode(getDataRequest.getPath()); if (n == null) { throw new KeeperException.NoNodeException(); } Long aclL; synchronized(n) { aclL = n.acl; } PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclL), ZooDefs.Perms.READ, request.authInfo); Stat stat = new Stat(); byte b[] = zks.getZKDatabase().getData(getDataRequest.getPath(), stat, getDataRequest.getWatch() ? cnxn : null); rsp = new GetDataResponse(b, stat); break; } case OpCode.setWatches: { lastOp = "SETW"; SetWatches setWatches = new SetWatches(); // XXX We really should NOT need this!!!! request.request.rewind(); ByteBufferInputStream.byteBuffer2Record(request.request, setWatches); long relativeZxid = setWatches.getRelativeZxid(); zks.getZKDatabase().setWatches(relativeZxid, setWatches.getDataWatches(), setWatches.getExistWatches(), setWatches.getChildWatches(), cnxn); break; } case OpCode.getACL: { lastOp = "GETA"; GetACLRequest getACLRequest = new GetACLRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, getACLRequest); Stat stat = new Stat(); List<ACL> acl = zks.getZKDatabase().getACL(getACLRequest.getPath(), stat); rsp = new GetACLResponse(acl, stat); break; } case OpCode.getChildren: { lastOp = "GETC"; GetChildrenRequest getChildrenRequest = new GetChildrenRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, getChildrenRequest); DataNode n = zks.getZKDatabase().getNode(getChildrenRequest.getPath()); if (n == null) { throw new KeeperException.NoNodeException(); } Long aclG; synchronized(n) { aclG = n.acl; } PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclG), ZooDefs.Perms.READ, request.authInfo); List<String> children = zks.getZKDatabase().getChildren( getChildrenRequest.getPath(), null, getChildrenRequest .getWatch() ? cnxn : null); rsp = new GetChildrenResponse(children); break; } case OpCode.getChildren2: { lastOp = "GETC"; GetChildren2Request getChildren2Request = new GetChildren2Request(); ByteBufferInputStream.byteBuffer2Record(request.request, getChildren2Request); Stat stat = new Stat(); DataNode n = zks.getZKDatabase().getNode(getChildren2Request.getPath()); if (n == null) { throw new KeeperException.NoNodeException(); } Long aclG; synchronized(n) { aclG = n.acl; } PrepRequestProcessor.checkACL(zks, zks.getZKDatabase().convertLong(aclG), ZooDefs.Perms.READ, request.authInfo); List<String> children = zks.getZKDatabase().getChildren( getChildren2Request.getPath(), stat, getChildren2Request .getWatch() ? cnxn : null); rsp = new GetChildren2Response(children, stat); break; } case OpCode.checkWatches: { lastOp = "CHKW"; CheckWatchesRequest checkWatches = new CheckWatchesRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, checkWatches); WatcherType type = WatcherType.fromInt(checkWatches.getType()); boolean containsWatcher = zks.getZKDatabase().containsWatcher( checkWatches.getPath(), type, cnxn); if (!containsWatcher) { String msg = String.format(Locale.ENGLISH, "%s (type: %s)", new Object[] { checkWatches.getPath(), type }); throw new KeeperException.NoWatcherException(msg); } break; } case OpCode.removeWatches: { lastOp = "REMW"; RemoveWatchesRequest removeWatches = new RemoveWatchesRequest(); ByteBufferInputStream.byteBuffer2Record(request.request, removeWatches); WatcherType type = WatcherType.fromInt(removeWatches.getType()); boolean removed = zks.getZKDatabase().removeWatch( removeWatches.getPath(), type, cnxn); if (!removed) { String msg = String.format(Locale.ENGLISH, "%s (type: %s)", new Object[] { removeWatches.getPath(), type }); throw new KeeperException.NoWatcherException(msg); } break; } } } catch (SessionMovedException e) { // session moved is a connection level error, we need to tear // down the connection otw ZOOKEEPER-710 might happen // ie client on slow follower starts to renew session, fails // before this completes, then tries the fast follower (leader) // and is successful, however the initial renew is then // successfully fwd/processed by the leader and as a result // the client and leader disagree on where the client is most // recently attached (and therefore invalid SESSION MOVED generated) cnxn.sendCloseSession(); return; } catch (KeeperException e) { err = e.code(); } catch (Exception e) { // log at error level as we are returning a marshalling // error to the user LOG.error("Failed to process " + request, e); StringBuilder sb = new StringBuilder(); ByteBuffer bb = request.request; bb.rewind(); while (bb.hasRemaining()) { sb.append(Integer.toHexString(bb.get() & 0xff)); } LOG.error("Dumping request buffer: 0x" + sb.toString()); err = Code.MARSHALLINGERROR; } long lastZxid = zks.getZKDatabase().getDataTreeLastProcessedZxid(); ReplyHeader hdr = new ReplyHeader(request.cxid, lastZxid, err.intValue()); zks.serverStats().updateLatency(request.createTime); cnxn.updateStatsForResponse(request.cxid, lastZxid, lastOp, request.createTime, Time.currentElapsedTime()); try { cnxn.sendResponse(hdr, rsp, "response"); if (request.type == OpCode.closeSession) { cnxn.sendCloseSession(); } } catch (IOException e) { LOG.error("FIXMSG",e); } }
第一步，根据共享的outstandingChanges，
先处理事务后处理session：
private ProcessTxnResult processTxn(Request request, TxnHeader hdr, Record txn) { ProcessTxnResult rc; int opCode = request != null ? request.type : hdr.getType(); long sessionId = request != null ? request.sessionId : hdr.getClientId(); if (hdr != null) { rc = getZKDatabase().processTxn(hdr, txn); } else { rc = new ProcessTxnResult(); } if (opCode == OpCode.createSession) { if (hdr != null && txn instanceof CreateSessionTxn) { CreateSessionTxn cst = (CreateSessionTxn) txn; sessionTracker.addGlobalSession(sessionId, cst.getTimeOut()); } else if (request != null && request.isLocalSession()) { request.request.rewind(); int timeout = request.request.getInt(); request.request.rewind(); sessionTracker.addSession(request.sessionId, timeout); } else { LOG.warn("*****>>>>> Got " + txn.getClass() + " " + txn.toString()); } } else if (opCode == OpCode.closeSession) { sessionTracker.removeSession(sessionId); } return rc; }
处理事务，本地和数据库的不同分支， DataTree创建节点
CreateTxn createTxn = (CreateTxn) txn; rc.path = createTxn.getPath(); createNode( createTxn.getPath(), createTxn.getData(), createTxn.getAcl(), createTxn.getEphemeral() ? header.getClientId() : 0, createTxn.getParentCVersion(), header.getZxid(), header.getTime(), null); break;
新增一个节点的逻辑是：
/** * Add a new node to the DataTree. * @param path * Path for the new node. * @param data * Data to store in the node. * @param acl * Node acls * @param ephemeralOwner * the session id that owns this node. -1 indicates this is not * an ephemeral node. * @param zxid * Transaction ID * @param time * @param outputStat * A Stat object to store Stat output results into. * @throws NodeExistsException * @throws NoNodeException * @throws KeeperException */ public void createNode(final String path, byte data[], List<ACL> acl, long ephemeralOwner, int parentCVersion, long zxid, long time, Stat outputStat) throws KeeperException.NoNodeException, KeeperException.NodeExistsException { int lastSlash = path.lastIndexOf('/'); String parentName = path.substring(0, lastSlash); String childName = path.substring(lastSlash + 1); StatPersisted stat = new StatPersisted(); stat.setCtime(time); stat.setMtime(time); stat.setCzxid(zxid); stat.setMzxid(zxid); stat.setPzxid(zxid); stat.setVersion(0); stat.setAversion(0); stat.setEphemeralOwner(ephemeralOwner); DataNode parent = nodes.get(parentName); if (parent == null) { throw new KeeperException.NoNodeException(); } synchronized (parent) { Set<String> children = parent.getChildren(); if (children != null && children.contains(childName)) { throw new KeeperException.NodeExistsException(); } if (parentCVersion == -1) { parentCVersion = parent.stat.getCversion(); parentCVersion++; } parent.stat.setCversion(parentCVersion); parent.stat.setPzxid(zxid); Long longval = convertAcls(acl); DataNode child = new DataNode(data, longval, stat); parent.addChild(childName); nodes.put(path, child); if (ephemeralOwner == CONTAINER_EPHEMERAL_OWNER) { containers.add(path); } else if (ephemeralOwner != 0) { HashSet<String> list = ephemerals.get(ephemeralOwner); if (list == null) { list = new HashSet<String>(); ephemerals.put(ephemeralOwner, list); } synchronized (list) { list.add(path); } } if (outputStat != null) { child.copyStat(outputStat); } } // now check if its one of the zookeeper node child if (parentName.startsWith(quotaZookeeper)) { // now check if its the limit node if (Quotas.limitNode.equals(childName)) { // this is the limit node // get the parent and add it to the trie pTrie.addPath(parentName.substring(quotaZookeeper.length())); } if (Quotas.statNode.equals(childName)) { updateQuotaForPath(parentName .substring(quotaZookeeper.length())); } } // also check to update the quotas for this node String lastPrefix = getMaxPrefixWithQuota(path); if(lastPrefix != null) { // ok we have some match and need to update updateCount(lastPrefix, 1); updateBytes(lastPrefix, data == null ? 0 : data.length); } dataWatches.triggerWatch(path, Event.EventType.NodeCreated); childWatches.triggerWatch(parentName.equals("") ? "/" : parentName, Event.EventType.NodeChildrenChanged); }
最后的逻辑是触发创建节点和子节点改变事件。
Set<Watcher> triggerWatch(String path, EventType type, Set<Watcher> supress) { WatchedEvent e = new WatchedEvent(type, KeeperState.SyncConnected, path); HashSet<Watcher> watchers; synchronized (this) { watchers = watchTable.remove(path); if (watchers == null || watchers.isEmpty()) { if (LOG.isTraceEnabled()) { ZooTrace.logTraceMessage(LOG, ZooTrace.EVENT_DELIVERY_TRACE_MASK, "No watchers for " + path); } return null; } for (Watcher w : watchers) { HashSet<String> paths = watch2Paths.get(w); if (paths != null) { paths.remove(path); } } } for (Watcher w : watchers) { if (supress != null && supress.contains(w)) { continue; } w.process(e); } return watchers; }
WatcherManager调用定义的watcher进行事件处理。
1.3. 再看异步消息处理器SyncRequestProcessor
@Override public void run() { try { int logCount = 0; // we do this in an attempt to ensure that not all of the servers // in the ensemble take a snapshot at the same time int randRoll = r.nextInt(snapCount/2); while (true) { Request si = null; if (toFlush.isEmpty()) { si = queuedRequests.take(); } else { si = queuedRequests.poll(); if (si == null) { flush(toFlush); continue; } } if (si == requestOfDeath) { break; } if (si != null) { // track the number of records written to the log if (zks.getZKDatabase().append(si)) { logCount++; if (logCount > (snapCount / 2 + randRoll)) { randRoll = r.nextInt(snapCount/2); // roll the log zks.getZKDatabase().rollLog(); // take a snapshot if (snapInProcess != null && snapInProcess.isAlive()) { LOG.warn("Too busy to snap, skipping"); } else { snapInProcess = new ZooKeeperThread("Snapshot Thread") { public void run() { try { zks.takeSnapshot(); } catch(Exception e) { LOG.warn("Unexpected exception", e); } } }; snapInProcess.start(); } logCount = 0; } } else if (toFlush.isEmpty()) { // optimization for read heavy workloads // iff this is a read, and there are no pending // flushes (writes), then just pass this to the next // processor if (nextProcessor != null) { nextProcessor.processRequest(si); if (nextProcessor instanceof Flushable) { ((Flushable)nextProcessor).flush(); } } continue; } toFlush.add(si); if (toFlush.size() > 1000) { flush(toFlush); } } } } catch (Throwable t) { handleException(this.getName(), t); } finally{ running = false; } LOG.info("SyncRequestProcessor exited!"); }
异步处理日志和快照，启动ZooKeeperThread线程来生成快照。
public void takeSnapshot(){ try { txnLogFactory.save(zkDb.getDataTree(), zkDb.getSessionWithTimeOuts()); } catch (IOException e) { LOG.error("Severe unrecoverable error, exiting", e); // This is a severe error that we cannot recover from, // so we need to exit System.exit(10); } }
FileTxnSnapLog是个工具类，帮助处理txtlog和snapshot。
/** * save the datatree and the sessions into a snapshot * @param dataTree the datatree to be serialized onto disk * @param sessionsWithTimeouts the sesssion timeouts to be * serialized onto disk * @throws IOException */ public void save(DataTree dataTree, ConcurrentHashMap<Long, Integer> sessionsWithTimeouts) throws IOException { long lastZxid = dataTree.lastProcessedZxid; File snapshotFile = new File(snapDir, Util.makeSnapshotName(lastZxid)); LOG.info("Snapshotting: 0x{} to {}", Long.toHexString(lastZxid), snapshotFile); snapLog.serialize(dataTree, sessionsWithTimeouts, snapshotFile); }
持久化为文件
/** * serialize the datatree and session into the file snapshot * @param dt the datatree to be serialized * @param sessions the sessions to be serialized * @param snapShot the file to store snapshot into */ public synchronized void serialize(DataTree dt, Map<Long, Integer> sessions, File snapShot) throws IOException { if (!close) { OutputStream sessOS = new BufferedOutputStream(new FileOutputStream(snapShot)); CheckedOutputStream crcOut = new CheckedOutputStream(sessOS, new Adler32()); //CheckedOutputStream cout = new CheckedOutputStream() OutputArchive oa = BinaryOutputArchive.getArchive(crcOut); FileHeader header = new FileHeader(SNAP_MAGIC, VERSION, dbId); serialize(dt,sessions,oa, header); long val = crcOut.getChecksum().getValue(); oa.writeLong(val, "val"); oa.writeString("/", "path"); sessOS.flush(); crcOut.close(); sessOS.close(); } }
至此，整个流程已经走完。
2. 集群情况下
集群情况和单机略有不同，集群中使用QuorumPeer来启动ServerCnxnFactory，绑定本地地址
@Override public void start() { LOG.info("binding to port " + localAddress); parentChannel = bootstrap.bind(localAddress); }
限于篇幅，后面的逻辑将在下篇中详细描述。
小结
从上面的代码流程中，我们可以看出服务器处理请求要么通过Noi要不通过框架Netty来处理请求，请求通过先通过PrepRequestProcessor接收请求，并进行包装，然后请求类型的不同，设置同享数据；然后通过SyncRequestProcessor来序列化快照和事务日志，并根据命令类型改变db的内容，在日志和快照没有写入前不会进行下一个消息处理器；最后调用FinalRequestProcessor来作为消息处理器的终结者，发送响应消息，并触发watcher的处理程序 。
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