深入浅出Zookeeper之四Create请求和处理
客户端接口
public String create(final String path, byte data[], List<ACL> acl,
CreateMode createMode)
throws KeeperException, InterruptedException
{
final String clientPath = path;
PathUtils.validatePath(clientPath, createMode.isSequential());
final String serverPath = prependChroot(clientPath);
//请求头
RequestHeader h = new RequestHeader();
h.setType(ZooDefs.OpCode.create);
//请求体
CreateRequest request = new CreateRequest();
//CREATE请求需要server端响应
CreateResponse response = new CreateResponse();
request.setData(data);
//node类型
request.setFlags(createMode.toFlag());
request.setPath(serverPath);
if (acl != null && acl.size() == 0) {
throw new KeeperException.InvalidACLException();
}
request.setAcl(acl);
//同步提交
ReplyHeader r = cnxn.submitRequest(h, request, response, null);
//异常情况
if (r.getErr() != 0) {
throw KeeperException.create(KeeperException.Code.get(r.getErr()),
clientPath);
}
//真实路径，对于SEQUENTIAL NODE后面会加上序号
if (cnxn.chrootPath == null) {
return response.getPath();
} else {
return response.getPath().substring(cnxn.chrootPath.length());
}
}
请求提交过程和之前的exists一样，都是通过sendthread写出去，都会进入pengding队列等待server端返回。
server端处理也是一样，变化的只是RequestProcessor的业务逻辑。也就是说transport层是通用的，变化的是上层的业务层。
server端执行处理链，PrepRequestProcessor
switch (request.type) {
case OpCode.create:
//反序列化的对象
CreateRequest createRequest = new CreateRequest();
//zxid递增
pRequest2Txn(request.type, zks.getNextZxid(), request, createRequest, true);
break;
......
request.zxid = zks.getZxid();
nextProcessor.processRequest(request);
具体处理
protected void pRequest2Txn(int type, long zxid, Request request, Record record, boolean deserialize)
throws KeeperException, IOException, RequestProcessorException
{
//构造内部的事务头
request.hdr = new TxnHeader(request.sessionId, request.cxid, zxid,
zks.getTime(), type);
switch (type) {
case OpCode.create:
//检查session是否还有效
zks.sessionTracker.checkSession(request.sessionId, request.getOwner());
CreateRequest createRequest = (CreateRequest)record;
//反序列化
if(deserialize)
ByteBufferInputStream.byteBuffer2Record(request.request, createRequest);
String path = createRequest.getPath();
//路径规则检查
int lastSlash = path.lastIndexOf('/');
if (lastSlash == -1 || path.indexOf('\0') != -1 || failCreate) {
LOG.info("Invalid path " + path + " with session 0x" +
Long.toHexString(request.sessionId));
throw new KeeperException.BadArgumentsException(path);
}
//权限去重
List<ACL> listACL = removeDuplicates(createRequest.getAcl());
if (!fixupACL(request.authInfo, listACL)) {
throw new KeeperException.InvalidACLException(path);
}
String parentPath = path.substring(0, lastSlash);
//父节点的ChangeRecord
ChangeRecord parentRecord = getRecordForPath(parentPath);
//权限校验
checkACL(zks, parentRecord.acl, ZooDefs.Perms.CREATE,
request.authInfo);
int parentCVersion = parentRecord.stat.getCversion();
CreateMode createMode =
CreateMode.fromFlag(createRequest.getFlags());
//SEQUENCE节点修改路径
if (createMode.isSequential()) {
path = path + String.format(Locale.ENGLISH, "%010d", parentCVersion);
}
try {
PathUtils.validatePath(path);
} catch(IllegalArgumentException ie) {
LOG.info("Invalid path " + path + " with session 0x" +
Long.toHexString(request.sessionId));
throw new KeeperException.BadArgumentsException(path);
}
//当前节点ChangeRecord，一并校验节点是否已经存在
try {
if (getRecordForPath(path) != null) {
throw new KeeperException.NodeExistsException(path);
}
} catch (KeeperException.NoNodeException e) {
// ignore this one
}
//EPHEMERAL节点不允许创建子节点
boolean ephemeralParent = parentRecord.stat.getEphemeralOwner() != 0;
if (ephemeralParent) {
throw new KeeperException.NoChildrenForEphemeralsException(path);
}
//递增Cversion
int newCversion = parentRecord.stat.getCversion()+1;
//构造事务体，后续会被写入log
request.txn = new CreateTxn(path, createRequest.getData(),
listACL,
createMode.isEphemeral(), newCversion);
StatPersisted s = new StatPersisted();
//如果是临时节点，则owner为sessionId
if (createMode.isEphemeral()) {
s.setEphemeralOwner(request.sessionId);
}
parentRecord = parentRecord.duplicate(request.hdr.getZxid());
//递增parent的child数
parentRecord.childCount++;
//递增parent的cversion
parentRecord.stat.setCversion(newCversion);
//添加changeRecord到冗余队列
addChangeRecord(parentRecord);
addChangeRecord(new ChangeRecord(request.hdr.getZxid(), path, s,
0, listACL));
break;
......
SyncRequestProcessor处理，主要是log写入，和之前的分析类似，不赘述
FinalRequestProcessor处理，修改内存中的datatree结构
switch (header.getType()) {
case OpCode.create:
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());
break;
public String createNode(String path, byte data[], List<ACL> acl,
long ephemeralOwner, int parentCVersion, long zxid, long time)
throws KeeperException.NoNodeException,
KeeperException.NodeExistsException {
//各种参数设置
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();
}
//修改parent节点内容
synchronized (parent) {
Set<String> children = parent.getChildren();
if (children != null) {
if (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);
//添加目标节点
DataNode child = new DataNode(parent, data, longval, stat);
parent.addChild(childName);
nodes.put(path, child);
//添加ephemeral类型节点
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);
}
}
}
......
//dataWatches和childWatches事件触发
dataWatches.triggerWatch(path, Event.EventType.NodeCreated);
childWatches.triggerWatch(parentName.equals("") ? "/" : parentName,
Event.EventType.NodeChildrenChanged);
return path;
}
事件触发过程
public Set<Watcher> triggerWatch(String path, EventType type, Set<Watcher> supress) {
WatchedEvent e = new WatchedEvent(type,
KeeperState.SyncConnected, path);
HashSet<Watcher> watchers;
synchronized (this) {
//拿节点对应的watcher列表，只通知一次
watchers = watchTable.remove(path);
.......
for (Watcher w : watchers) {
HashSet<String> paths = watch2Paths.get(w);
if (paths != null) {
paths.remove(path);
}
}
}
//挨个通知
for (Watcher w : watchers) {
if (supress != null && supress.contains(w)) {
continue;
}
w.process(e);
}
return watchers;
}
具体处理，NIOServerCncx
synchronized public void process(WatchedEvent event) {
//事件通知的响应头
ReplyHeader h = new ReplyHeader(-1, -1L, 0);
......
// Convert WatchedEvent to a type that can be sent over the wire
WatcherEvent e = event.getWrapper();
//发送响应
sendResponse(h, e, "notification");
}
具体发送：
synchronized public void sendResponse(ReplyHeader h, Record r, String tag) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// Make space for length
BinaryOutputArchive bos = BinaryOutputArchive.getArchive(baos);
try {
//占位
baos.write(fourBytes);
//序列化
bos.writeRecord(h, "header");
if (r != null) {
bos.writeRecord(r, tag);
}
baos.close();
} catch (IOException e) {
LOG.error("Error serializing response");
}
//转换成byte数组
byte b[] = baos.toByteArray();
ByteBuffer bb = ByteBuffer.wrap(b);
//最后写入长度
bb.putInt(b.length - 4).rewind();
//通过channel异步写
sendBuffer(bb);
if (h.getXid() > 0) {
synchronized(this){
outstandingRequests--;
}
// check throttling
synchronized (this.factory) {
if (zkServer.getInProcess() < outstandingLimit
|| outstandingRequests < 1) {
sk.selector().wakeup();
enableRecv();
}
}
}
} catch(Exception e) {
LOG.warn("Unexpected exception. Destruction averted.", e);
}
}
server端就处理完了，接下来client端SendThread收到响应
if (replyHdr.getXid() == -1) {
// -1 means notification
if (LOG.isDebugEnabled()) {
LOG.debug("Got notification sessionid:0x"
+ Long.toHexString(sessionId));
}
//反序列化
WatcherEvent event = new WatcherEvent();
event.deserialize(bbia, "response");
// convert from a server path to a client path
//路径切换，如果client用了相对路径的话
if (chrootPath != null) {
String serverPath = event.getPath();
if(serverPath.compareTo(chrootPath)==0)
event.setPath("/");
else if (serverPath.length() > chrootPath.length())
event.setPath(serverPath.substring(chrootPath.length()));
else {
LOG.warn("Got server path " + event.getPath()
+ " which is too short for chroot path "
+ chrootPath);
}
}
//通过eventThread派发事件，通知之前注册的watcher
WatchedEvent we = new WatchedEvent(event);
if (LOG.isDebugEnabled()) {
LOG.debug("Got " + we + " for sessionid 0x"
+ Long.toHexString(sessionId));
}
eventThread.queueEvent( we );
return;
}
eventThread端处理和之前类似
case NodeCreated:
//通知dataWatcher，只一次
synchronized (dataWatches) {
addTo(dataWatches.remove(clientPath), result);
}
//通知existWatcher，只一次
synchronized (existWatches) {
addTo(existWatches.remove(clientPath), result);
}
break;
if (event instanceof WatcherSetEventPair) {
// each watcher will process the event
WatcherSetEventPair pair = (WatcherSetEventPair) event;
//挨个通知
for (Watcher watcher : pair.watchers) {
try {
watcher.process(pair.event);
} catch (Throwable t) {
LOG.error("Error while calling watcher ", t);
}
}
} 以上就完成了create操作的处理，之后的delete，set，get操作都是类似的，大家有兴趣的直接阅读相关代码即可:)