文章目錄
前言
**Server端 **
(Cat-consumer 用於實時分析從客戶端提供的數據\Cat-home 作爲用戶給用戶提供展示的控制端
,並且Cat-home做展示時,通過對Cat-Consumer的調用獲取其他節點的數據,將所有數據彙總展示
consumer、home以及路由中心都是部署在一起的,每個服務端節點都可以充當任何一個角色)
**Client端 **
(Cat-client 提供給業務以及中間層埋點的底層SDK)
相關文章:
[分佈式監控CAT] Server端源碼解析——初始化
[分佈式監控CAT] Client端—定製化SDK\自動埋點實現
[分佈式監控CAT] Client端源碼解析
[分佈式監控CAT] Server端源碼解析——消息消費\報表處理
Client端
cat-client模塊的包結構
└─com
├─dianping
│ └─cat
│ ├─build
│ ├─configuration
│ ├─log4j
│ ├─message
│ │ ├─internal
│ │ ├─io
│ │ └─spi
│ │ ├─codec
│ │ └─internal
│ ├─servlet
│ └─status
└─site
├─helper
└─lookup
└─util
Client模塊架構圖
類圖
源碼閱讀
閱讀思路:
我們通過一個測試用例,debug來理解源碼。
//靜態方法獲取Transaction對象
Transaction t=Cat.newTransaction("logTransaction", "logTransaction");
TimeUnit.SECONDS.sleep(30);
t.setStatus("0");
t.complete();
接着我們着重看看關鍵代碼:
Cat.java
private static Cat s_instance = new Cat();
private static volatile boolean s_init = false;
private static void checkAndInitialize() {
if (!s_init) {
synchronized (s_instance) {
if (!s_init) {
initialize(new File(getCatHome(), "client.xml"));
log("WARN", "Cat is lazy initialized!");
s_init = true;
}
}
}
}
private Cat() {
}
public static MessageProducer getProducer() {
checkAndInitialize();
return s_instance.m_producer;
}
Cat lazy Init
可以看到類加載時已經完成了Cat對象的初始化,內存中有且僅有一個Cat Object(static Cat s_instance = new Cat();),但是包含配置信息的完整的Cat對象並沒有完全初始化完成。調用Cat時會先嚐試獲取producer對象,並在獲取之前檢查客戶端配置是否加載完畢(checkAndInitialize)。
checkAndInitialize()通過使用doublecheck來對Cat相關配置填充的單次初始化加載。
1.cat-client首先會使用plexus(一個比較老的IOC容器)加載配置文件/META-INF/plexus/plexus.xml,完成IOC容器的初始化。
2.接着使用…/…/client.xml文件完成cat對象的配置信息填充初始化。並且啓動這四個daemon線程,後文詳細說明:
cat-StatusUpdateTask 用來每秒鐘上報客戶端基本信息(JVM等信息)
cat-merge-atomic-task(消息合併檢查)
cat-TcpSocketSender-ChannelManager(NIO 連接服務端檢查)
cat-TcpSocketSender(消息發送服務端)
CatClientModule
public class CatClientModule extends AbstractModule {
public static final String ID = "cat-client";
@Override
protected void execute(final ModuleContext ctx) throws Exception {
ctx.info("Current working directory is " + System.getProperty("user.dir"));
// initialize milli-second resolution level timer
MilliSecondTimer.initialize();
// tracking thread start/stop,此處增加經典的hook,用於線程池關閉的清理工作。
Threads.addListener(new CatThreadListener(ctx));
// warm up Cat
Cat.getInstance().setContainer(((DefaultModuleContext) ctx).getContainer());
// bring up TransportManager
ctx.lookup(TransportManager.class);
ClientConfigManager clientConfigManager = ctx.lookup(ClientConfigManager.class);
if (clientConfigManager.isCatEnabled()) {
// start status update task
StatusUpdateTask statusUpdateTask = ctx.lookup(StatusUpdateTask.class);
Threads.forGroup("cat").start(statusUpdateTask);
LockSupport.parkNanos(10 * 1000 * 1000L); // wait 10 ms
// MmapConsumerTask mmapReaderTask = ctx.lookup(MmapConsumerTask.class);
// Threads.forGroup("cat").start(mmapReaderTask);
}
}
這裏plexusIOC的具體的初始化加載邏輯在org\unidal\framework\foundation-service\2.5.0\foundation-service-2.5.0.jar中,有興趣可以仔細查看。
當準備工作做完之後,會執行具體的消息構造:
消息構造
DefaultMessageProducer.newTransaction(String type, String name)
@Override
public Transaction newTransaction(String type, String name) {
// this enable CAT client logging cat message without explicit setup
if (!m_manager.hasContext()) {
//詳細可見下文源碼,此處就是用ThreadLocal存儲一個Context對象:ctx = new Context(m_domain.getId(), m_hostName, m_domain.getIp());
m_manager.setup();
}
if (m_manager.isMessageEnabled()) {
DefaultTransaction transaction = new DefaultTransaction(type, name, m_manager);
//向Context中填充構造的消息體:Context.m_tree;Context.m_stack;稍後看看Context這個對象
m_manager.start(transaction, false);
return transaction;
} else {
return NullMessage.TRANSACTION;
}
}
DefaultMessageManager.start(Transaction transaction, boolean forked)
@Override
public void start(Transaction transaction, boolean forked) {
Context ctx = getContext();//這裏獲取上文中說到的ThreadLocal中構造的Context對象
if (ctx != null) {
ctx.start(transaction, forked);
if (transaction instanceof TaggedTransaction) {
TaggedTransaction tt = (TaggedTransaction) transaction;
m_taggedTransactions.put(tt.getTag(), tt);
}
} else if (m_firstMessage) {
m_firstMessage = false;
m_logger.warn("CAT client is not enabled because it's not initialized yet");
}
}
DefaultMessageManager.Context.start(Transaction transaction, boolean forked)
public void start(Transaction transaction, boolean forked) {
if (!m_stack.isEmpty()) {//
{
Transaction parent = m_stack.peek();
addTransactionChild(transaction, parent);
}
} else {
m_tree.setMessage(transaction);//在這裏把返回的transaction放在tree上,如果有嵌套結構,後邊繼續在tree上添枝加葉
}
if (!forked) {
m_stack.push(transaction);
}
}
這部分代碼可以看出,
通過ThreadLocal<.Context.>,使Context中實際的消息的構造保證了線程安全。
如果當前Context的棧m_stack不爲空,那麼接着之前的消息後邊,將當前消息構造爲一個孩子結點。如果當前消息之前沒有其他消息,放入m_stack中,並setMessage.也就是當前消息時父節點。
至此,消息體構造完畢。
這裏需要看一下Context類,是DefaultMessageManager包私有的內部類。
Context.java
class Context {
private MessageTree m_tree;//初始化的時候構建一個MessageTree
private Stack<Transaction> m_stack;
private int m_length;
private boolean m_traceMode;
private long m_totalDurationInMicros; // for truncate message
private Set<Throwable> m_knownExceptions;
public Context(String domain, String hostName, String ipAddress) {
m_tree = new DefaultMessageTree();
m_stack = new Stack<Transaction>();
Thread thread = Thread.currentThread();
String groupName = thread.getThreadGroup().getName();
m_tree.setThreadGroupName(groupName);
m_tree.setThreadId(String.valueOf(thread.getId()));
m_tree.setThreadName(thread.getName());
m_tree.setDomain(domain);
m_tree.setHostName(hostName);
m_tree.setIpAddress(ipAddress);
m_length = 1;
m_knownExceptions = new HashSet<Throwable>();
}
每個線程通過使用ThreadLocal構造一個Context對象並存儲。Context主要包含當前的消息體m_tree,和多個嵌套消息體填充的棧:m_stack 。
再回到我們原來的UnitTest代碼,
Transaction t=Cat.newTransaction("logTransaction", "logTransaction");
這行代碼完成了客戶端plexusIOC容器的初始化,cat-client的加載初始化、啓動了四個daemon線程,並返回了Transaction對象。
t.setStatus("0");//很簡單,就是這是一個屬性值
t.complete();
消息完成後,將消息放入一個隊列中,從而保證異步上報。
transaction.complete();
complete的具體代碼如下:
........
public void complete() {
try {
if (isCompleted()) {
// complete() was called more than once
DefaultEvent event = new DefaultEvent("cat", "BadInstrument");
event.setStatus("TransactionAlreadyCompleted");
event.complete();
addChild(event);
} else {
m_durationInMicro = (System.nanoTime() - m_durationStart) / 1000L;
setCompleted(true);
if (m_manager != null) {
m_manager.end(this);
}
}
} catch (Exception e) {
// ignore
}
}
........
@Override
public void end(Transaction transaction) {
Context ctx = getContext();
if (ctx != null && transaction.isStandalone()) {
if (ctx.end(this, transaction)) {
m_context.remove();
}
}
}
........
public boolean end(DefaultMessageManager manager, Transaction transaction) {
if (!m_stack.isEmpty()) {
Transaction current = m_stack.pop();//Context的成員變量m_stack彈出棧頂元素,LIFO當然是最新的current元素。
if (transaction == current) {
m_validator.validate(m_stack.isEmpty() ? null : m_stack.peek(), current);
} else {
while (transaction != current && !m_stack.empty()) {
m_validator.validate(m_stack.peek(), current);
current = m_stack.pop();
}
}
if (m_stack.isEmpty()) {//如果當前線程存儲的Context中m_stack無元素
MessageTree tree = m_tree.copy();
m_tree.setMessageId(null);//清理m_tree
m_tree.setMessage(null);
if (m_totalDurationInMicros > 0) {
adjustForTruncatedTransaction((Transaction) tree.getMessage());
}
manager.flush(tree);//將消息放入消費隊列中
return true;
}
}
return false;
}
........
public void flush(MessageTree tree) {
if (tree.getMessageId() == null) {
tree.setMessageId(nextMessageId());//爲消息體生產全局唯一ID,詳見snowflate算法
}
MessageSender sender = m_transportManager.getSender();
if (sender != null && isMessageEnabled()) {
sender.send(tree);
reset();//ThreadLocal中存儲的Context清理
} else {
m_throttleTimes++;
if (m_throttleTimes % 10000 == 0 || m_throttleTimes == 1) {
m_logger.info("Cat Message is throttled! Times:" + m_throttleTimes);
}
}
}
........
private Context getContext() {
if (Cat.isInitialized()) {
Context ctx = m_context.get();//ThreadLocal存儲一個Context對象
if (ctx != null) {
return ctx;
} else {
if (m_domain != null) {
ctx = new Context(m_domain.getId(), m_hostName, m_domain.getIp());
} else {
ctx = new Context("Unknown", m_hostName, "");
}
m_context.set(ctx);
return ctx;
}
}
return null;
}
//TcpSocketSender.send(MessageTree tree)
private MessageQueue m_queue = new DefaultMessageQueue(SIZE);
private MessageQueue m_atomicTrees = new DefaultMessageQueue(SIZE);
@Override
public void send(MessageTree tree) {
if (isAtomicMessage(tree)) {
boolean result = m_atomicTrees.offer(tree, m_manager.getSample());
if (!result) {
logQueueFullInfo(tree);
}
} else {
boolean result = m_queue.offer(tree, m_manager.getSample());
if (!result) {
logQueueFullInfo(tree);
}
}
}
至此,構造的消息體放入了阻塞隊列中等待上傳。如圖左邊。
CAT客戶端在收集端數據方面使用ThreadLocal(線程局部變量),是線程本地變量。保證了線程安全。
爲什麼這樣設計,基於ThreadLocal收集消息?
業務方在處理業務邏輯時基本都是在一個線程內部調用後端服務、數據庫、緩存等,將這些數據拿回來再進行業務邏輯封裝,最後將結果展示給用戶。所以將監控請求作爲一個監控上下文存入線程變量就非常合適。
(此圖源自作者的公開分享,原圖來源請點擊此處)
總結
至此,我們可以看到Cat-SDK通過ThreadLocal對消息進行收集,
收集進來按照時間以及類型構造爲Tree結構,在compele()方法中將這個構造的消息放入一個內存隊列中,等待TcpSockekSender這個Daemon線程異步上報給服務端。
接着我們來看看消息上傳服務端的代碼,這裏會有一個線程cat-TcpSocketSender監聽消費隊列,並消費(上傳服務端):
通信上報服務端使用了Netty-Client,並且自定義了消息協議。
TcpSocketSender.java
@Override
public void run() {
m_active = true;
while (m_active) {
ChannelFuture channel = m_manager.channel();
if (channel != null && checkWritable(channel)) {
try {
MessageTree tree = m_queue.poll();
if (tree != null) {
sendInternal(tree);//netty NIO編碼後TCP發送到服務端。
tree.setMessage(null);
}
} catch (Throwable t) {
m_logger.error("Error when sending message over TCP socket!", t);
}
} else {
long current = System.currentTimeMillis();
long oldTimestamp = current - HOUR;
while (true) {
try {
MessageTree tree = m_queue.peek();
if (tree != null && tree.getMessage().getTimestamp() < oldTimestamp) {
MessageTree discradTree = m_queue.poll();
if (discradTree != null) {
m_statistics.onOverflowed(discradTree);
}
} else {
break;
}
} catch (Exception e) {
m_logger.error(e.getMessage(), e);
break;
}
}
try {
Thread.sleep(5);
} catch (Exception e) {
// ignore it
m_active = false;
}
}
}
}
private void sendInternal(MessageTree tree) {
ChannelFuture future = m_manager.channel();
ByteBuf buf = PooledByteBufAllocator.DEFAULT.buffer(10 * 1024); // 10K
System.out.println(tree);
m_codec.encode(tree, buf);//編碼後發送
int size = buf.readableBytes();
Channel channel = future.channel();
channel.writeAndFlush(buf);
if (m_statistics != null) {
m_statistics.onBytes(size);
}
}
接下來我們着重看看,隨着cat-client加載啓動的幾個daemon Thread後臺線程:
cat-merge-atomic-task
接上文,符合如下邏輯判斷的atomicMessage會放入m_atomicTrees消息隊列,然後由這個後臺線程監聽並消費。
具體代碼如下:
TcpSocketSender.java
private MessageQueue m_atomicTrees = new DefaultMessageQueue(SIZE);
......
private boolean isAtomicMessage(MessageTree tree) {
Message message = tree.getMessage();//從tree上拿去message
if (message instanceof Transaction) {//如果這個message實現了Transaction接口,也就是Transaction類型的消息
String type = message.getType();
if (type.startsWith("Cache.") || "SQL".equals(type)) {//如果以Cache.,SQL開頭的則返回True
return true;
} else {
return false;
}
} else {
return true;
}
//看到這裏,也就是說,"Cache","SQL"開頭的Transaction消息,或者非Transaction消息,認爲是atomicMessage.
}
......
public void send(MessageTree tree) {
if (isAtomicMessage(tree)) {//如果符合atomicMessage
boolean result = m_atomicTrees.offer(tree, m_manager.getSample());
if (!result) {
logQueueFullInfo(tree);//隊列溢出處理
}
} else {
boolean result = m_queue.offer(tree, m_manager.getSample());
if (!result) {
logQueueFullInfo(tree);
}
}
}
......
public class DefaultMessageQueue implements MessageQueue {
private BlockingQueue<MessageTree> m_queue;
private AtomicInteger m_count = new AtomicInteger();
public DefaultMessageQueue(int size) {
m_queue = new LinkedBlockingQueue<MessageTree>(size);
}
@Override
public boolean offer(MessageTree tree) {
return m_queue.offer(tree);
}
@Override
public boolean offer(MessageTree tree, double sampleRatio) {
if (tree.isSample() && sampleRatio < 1.0) {//如果這個消息是sample,並且sampleRation大於1
if (sampleRatio > 0) {//這段邏輯就是按採樣率去剔除一些消息,只選取其中一部分進行後續的消費上傳。
int count = m_count.incrementAndGet();
if (count % (1 / sampleRatio) == 0) {
return offer(tree);
}
}
return false;
} else {//不做採樣過濾,放入隊列
return offer(tree);
}
}
@Override
public MessageTree peek() {
return m_queue.peek();
}
@Override
public MessageTree poll() {
try {
return m_queue.poll(5, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
return null;
}
}
@Override
public int size() {
return m_queue.size();
}
}
接下來,看看這個後臺進程的消費動作:
......
private boolean shouldMerge(MessageQueue trees) {
MessageTree tree = trees.peek();//獲取對頭元素,非移除
if (tree != null) {
long firstTime = tree.getMessage().getTimestamp();
int maxDuration = 1000 * 30;
//消息在30s內生成,或者隊列擠壓消息超過200,則需要merge
if (System.currentTimeMillis() - firstTime > maxDuration || trees.size() >= MAX_CHILD_NUMBER) {
return true;
}
}
return false;
}
......
@Override
public void run() {
while (true) {
if (shouldMerge(m_atomicTrees)) {
MessageTree tree = mergeTree(m_atomicTrees);//把m_atomicTrees隊列中的消息merge爲一條消息樹
boolean result = m_queue.offer(tree);//放入m_queue隊列,等待cat-TcpSocketSender線程正常消費
if (!result) {
logQueueFullInfo(tree);
}
} else {
try {
Thread.sleep(5);
} catch (InterruptedException e) {
break;
}
}
}
}
.....
private MessageTree mergeTree(MessageQueue trees) {
int max = MAX_CHILD_NUMBER;
DefaultTransaction tran = new DefaultTransaction("_CatMergeTree", "_CatMergeTree", null);//增加merge處理埋點
MessageTree first = trees.poll();//從隊列頭部移除
tran.setStatus(Transaction.SUCCESS);
tran.setCompleted(true);
tran.addChild(first.getMessage());
tran.setTimestamp(first.getMessage().getTimestamp());
long lastTimestamp = 0;
long lastDuration = 0;
//這段邏輯就是不停從這個m_atomicTrees隊列頭部拿去messsage,並使用同一個messageId,把隊列中所有的消息合併爲一條Transaction消息。
while (max >= 0) {
MessageTree tree = trees.poll();//接着 從隊列頭部移除
if (tree == null) {
tran.setDurationInMillis(lastTimestamp - tran.getTimestamp() + lastDuration);
break;
}
lastTimestamp = tree.getMessage().getTimestamp();
if(tree.getMessage() instanceof DefaultTransaction){
lastDuration = ((DefaultTransaction) tree.getMessage()).getDurationInMillis();
} else {
lastDuration = 0;
}
tran.addChild(tree.getMessage());
m_factory.reuse(tree.getMessageId());
max--;
}
((DefaultMessageTree) first).setMessage(tran);
return first;
}
爲什麼要使用TCP協議
從上邊的代碼可以看到,CAT使用了TCP協議上報消息(引入了netty框架)。那麼爲什麼不適用http協議上報呢?
選擇TCP的理由:對於客戶端的數據採集儘量降低性能損耗,TCP協議比HTTP協議更加輕量級(比如TCP不需要header等額外的損耗),在高qps的場景下具備明顯的性能優勢。另外,CAT的設計也不需要保留一個
Http鏈接供外部調用,這樣的埋點方式效率低下,並不考慮。
TcpSocketSender-ChannelManager 後臺線程
這個線程是通過服務端配置的路由ip,10s輪詢一次,當滿足自旋n(n=m_count%30)次,去檢查路由服務端ip是否變動,並保證連接正常。
典型的拉取配置信息機制。
@Override
public void run() {
while (m_active) {
// make save message id index asyc
m_idfactory.saveMark();
checkServerChanged();// 每100s檢查連接信息(shouldCheckServerConfig),並進行連接,使用TCP協議建立長連接
ChannelFuture activeFuture = m_activeChannelHolder.getActiveFuture();//根據服務端配置的路由,獲取其中一個服務端ip並建立連接.
try {
} catch (Exception e) {
e.printStackTrace();
}
List<InetSocketAddress> serverAddresses = m_activeChannelHolder.getServerAddresses();
doubleCheckActiveServer(activeFuture);//檢查當前連接是否正常
reconnectDefaultServer(activeFuture, serverAddresses);//如果不正常,則繼續嘗試建立其他連接。當所有default-server ip都無法連接時,默認會走backServer的Ip進行連接。
try {
Thread.sleep(10 * 1000L); // check every 10 seconds
} catch (InterruptedException e) {
}
}
}
....
private void checkServerChanged() {
if (shouldCheckServerConfig(++m_count)) {//每遍歷監聽n(n=m_count%30)次或者沒有成功的連接,則檢查連接信息
Pair<Boolean, String> pair = routerConfigChanged();
if (pair.getKey()) {
String servers = pair.getValue();
List<InetSocketAddress> serverAddresses = parseSocketAddress(servers);
ChannelHolder newHolder = initChannel(serverAddresses, servers);//建立連接
if (newHolder != null) {
if (newHolder.isConnectChanged()) {
ChannelHolder last = m_activeChannelHolder;
m_activeChannelHolder = newHolder;
closeChannelHolder(last);
m_logger.info("switch active channel to " + m_activeChannelHolder);
} else {
m_activeChannelHolder = newHolder;
}
}
}
}
}
private ChannelHolder initChannel(List<InetSocketAddress> addresses, String serverConfig) {
try {
int len = addresses.size();
for (int i = 0; i < len; i++) {//遍歷,連接成功返回
InetSocketAddress address = addresses.get(i);
String hostAddress = address.getAddress().getHostAddress();
ChannelHolder holder = null;
if (m_activeChannelHolder != null && hostAddress.equals(m_activeChannelHolder.getIp())) {//當前的鏈接ip和address一致,那麼就複用,否則新建立連接。(稍後關閉之前過期的連接。)
holder = new ChannelHolder();
holder.setActiveFuture(m_activeChannelHolder.getActiveFuture()).setConnectChanged(false);
} else {
ChannelFuture future = createChannel(address);
if (future != null) {
holder = new ChannelHolder();
holder.setActiveFuture(future).setConnectChanged(true);//true表示需要關閉之前的鏈接
}
}
if (holder != null) {
holder.setActiveIndex(i).setIp(hostAddress);
holder.setActiveServerConfig(serverConfig).setServerAddresses(addresses);
m_logger.info("success when init CAT server, new active holder" + holder.toString());
return holder;
}
}
} catch (Exception e) {
m_logger.error(e.getMessage(), e);
}
try {
StringBuilder sb = new StringBuilder();
for (InetSocketAddress address : addresses) {
sb.append(address.toString()).append(";");
}
m_logger.info("Error when init CAT server " + sb.toString());
} catch (Exception e) {
// ignore
}
return null;
}
private boolean shouldCheckServerConfig(int count) {
int duration = 30;
//m_activeChannelHolder.getActiveIndex() == -1表示關閉了當前連接
if (count % duration == 0 || m_activeChannelHolder.getActiveIndex() == -1) {
return true;
} else {
return false;
}
}
private Pair<Boolean, String> routerConfigChanged() {
String current = loadServerConfig();//獲取當前路由表中的服務地址信息。示例:ip1:2280;ip2:2280...;
//current不爲空 && 路由表中的配置沒有任何變化
if (!StringUtils.isEmpty(current) && !current.equals(m_activeChannelHolder.getActiveServerConfig())) {
return new Pair<Boolean, String>(true, current);
} else {
return new Pair<Boolean, String>(false, current);
}
}
private String loadServerConfig() {
try {
//使用http請求獲取路由表配置信息
//示例url:http://ip:port/cat/s/router?domain=someDomain&ip=當前客戶端ip&op=json
//返回的content :{"kvs":{"routers":"ip1:2280;ip2:2280;..;","sample":"1.0"}}
String url = m_configManager.getServerConfigUrl();
InputStream inputstream = Urls.forIO().readTimeout(2000).connectTimeout(1000).openStream(url);
String content = Files.forIO().readFrom(inputstream, "utf-8");
KVConfig routerConfig = (KVConfig) m_jsonBuilder.parse(content.trim(), KVConfig.class);
String current = routerConfig.getValue("routers");
m_sample = Double.valueOf(routerConfig.getValue("sample").trim());
return current.trim();
} catch (Exception e) {
// ignore
}
return null;
}
StatusUpdateTask 後臺線程
這個線程很簡單,類似傳統的agent,每分鐘上報關於應用的各種信息(OS、MXBean信息等等)。而且,在每次線程啓動時上報一個Reboot消息表示重啓動。
MessageId的設計
CAT消息的Message-ID格式applicationName-0a010680-375030-2,CAT消息一共分爲四段:
第一段是應用名applicationName。
第二段是當前這臺機器的IP的16進制格式:
if (m_ipAddress == null) {
String ip = NetworkInterfaceManager.INSTANCE.getLocalHostAddress();
List<String> items = Splitters.by(".").noEmptyItem().split(ip);
byte[] bytes = new byte[4];
for (int i = 0; i < 4; i++) {
bytes[i] = (byte) Integer.parseInt(items.get(i));
}
StringBuilder sb = new StringBuilder(bytes.length / 2);
for (byte b : bytes) {
//1.一個byte 8位
//2.先獲取高4位的16進制字符
//3.在獲取低4位的16進制數
sb.append(Integer.toHexString((b >> 4) & 0x0F));//通常使用0x0f來與一個整數進行&運算,來獲取該整數的最低4個bit位
sb.append(Integer.toHexString(b & 0x0F));
}
m_ipAddress = sb.toString();
第三段的375030,是系統當前時間除以小時得到的整點數。
第四段的2,是表示當前這個客戶端在當前小時的順序遞增號(AtomicInteger自增,每小時結束後重置)。
public String getNextId() {
String id = m_reusedIds.poll();
if (id != null) {
return id;
} else {
long timestamp = getTimestamp();
if (timestamp != m_timestamp) {
m_index = new AtomicInteger(0);
m_timestamp = timestamp;
}
int index = m_index.getAndIncrement();
StringBuilder sb = new StringBuilder(m_domain.length() + 32);
sb.append(m_domain);
sb.append('-');
sb.append(m_ipAddress);
sb.append('-');
sb.append(timestamp);
sb.append('-');
sb.append(index);
return sb.toString();
}
總之,同一個小時內、同一個domain、同一個ip , messageId的唯一性需要 AtomicInteger保證。
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