区块链技术
Sentinel
本文主要是介绍Sentinel，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！
使用
有关于sentinel的使用方法和工作原理，在官方文档中都有详细的介绍，并且源码中也已经给出了一系列的demo，以下是示例：
<dependency> <groupId>com.alibaba.csp</groupId> <artifactId>sentinel-core</artifactId> <version>1.4.0-SNAPSHOT</version></dependency>
public class AuthorityDemo { private static final String RESOURCE_NAME = "testABC"; public static void main(String[] args) {
System.out.println("========Testing for black list========");
initBlackRules();
testFor(RESOURCE_NAME, "appA");
testFor(RESOURCE_NAME, "appB");
testFor(RESOURCE_NAME, "appC");
testFor(RESOURCE_NAME, "appE");
System.out.println("========Testing for white list========");
initWhiteRules();
testFor(RESOURCE_NAME, "appA");
testFor(RESOURCE_NAME, "appB");
testFor(RESOURCE_NAME, "appC");
testFor(RESOURCE_NAME, "appE");
} private static void testFor(/*@NonNull*/ String resource, /*@NonNull*/ String origin) {
ContextUtil.enter(resource, origin);
Entry entry = null; try {
entry = SphU.entry(resource);
System.out.println(String.format("Passed for resource %s, origin is %s", resource, origin));
} catch (BlockException ex) {
System.err.println(String.format("Blocked for resource %s, origin is %s", resource, origin));
} finally { if (entry != null) {
entry.exit();
}
ContextUtil.exit();
}
} private static void initWhiteRules() {
AuthorityRule rule = new AuthorityRule();
rule.setResource(RESOURCE_NAME);
rule.setStrategy(RuleConstant.AUTHORITY_WHITE);
rule.setLimitApp("appA,appE");
AuthorityRuleManager.loadRules(Collections.singletonList(rule));
} private static void initBlackRules() {
AuthorityRule rule = new AuthorityRule();
rule.setResource(RESOURCE_NAME);
rule.setStrategy(RuleConstant.AUTHORITY_BLACK);
rule.setLimitApp("appA,appB");
AuthorityRuleManager.loadRules(Collections.singletonList(rule));
}
}原理
SphU.entry(resource);// SphU.javapublic static Entry entry(String name) throws BlockException { return Env.sph.entry(name, EntryType.OUT, 1, OBJECTS0);
}// Env.javapublic static final Sph sph = new CtSph();// CtSph.javapublic Entry entry(String name, EntryType type, int count, Object... args) throws BlockException {
StringResourceWrapper resource = new StringResourceWrapper(name, type); return entry(resource, count, args);
}入口其实就是在CtSph类的entry方法中。这里引出了一个“资源”的概念，“资源”在sentinel中可以是任何东西：服务，服务里的方法，甚至是一段代码，比如上面demo中的RESOURCE_NAME就是一个资源。当然这只是我们字面上理解的“资源”，sentinel对资源做了抽象，即：ResourceWrapper。比如这里的RESOURCE_NAME是一个字符串，所以对应StringResourceWrapper，StringResourceWrapper 是ResourceWrapper的子类。
entry的具体实现如下，前面是一些校验项目，重点关注lookProcessChain方法，其实就是ProcessorSlotChain的生成过程
public Entry entry(ResourceWrapper resourceWrapper, int count, Object... args) throws BlockException {
Context context = ContextUtil.getContext(); if (context instanceof NullContext) { // The {@link NullContext} indicates that the amount of context has exceeded the threshold,
// so here init the entry only. No rule checking will be done.
return new CtEntry(resourceWrapper, null, context);
} if (context == null) { // Using default context.
context = MyContextUtil.myEnter(Constants.CONTEXT_DEFAULT_NAME, "", resourceWrapper.getType());
} // Global switch is close, no rule checking will do.
if (!Constants.ON) { return new CtEntry(resourceWrapper, null, context);
}
ProcessorSlot<Object> chain = lookProcessChain(resourceWrapper); /*
* Means amount of resources (slot chain) exceeds {@link Constants.MAX_SLOT_CHAIN_SIZE},
* so no rule checking will be done.
*/
if (chain == null) { return new CtEntry(resourceWrapper, null, context);
}
Entry e = new CtEntry(resourceWrapper, chain, context); try {
chain.entry(context, resourceWrapper, null, count, args);
} catch (BlockException e1) {
e.exit(count, args); throw e1;
} catch (Throwable e1) { // This should not happen, unless there are errors existing in Sentinel internal.
RecordLog.info("Sentinel unexpected exception", e1);
} return e;
}ProcessorSlotChain生成
ProcessorSlot<Object> chain = lookProcessChain(resourceWrapper);
ProcessorSlot<Object> lookProcessChain(ResourceWrapper resourceWrapper) {
ProcessorSlotChain chain = chainMap.get(resourceWrapper); // 双重校验
if (chain == null) {
synchronized (LOCK) {
chain = chainMap.get(resourceWrapper); if (chain == null) { // Entry size limit.
if (chainMap.size() >= Constants.MAX_SLOT_CHAIN_SIZE) { return null;
}
chain = SlotChainProvider.newSlotChain(); Map<ResourceWrapper, ProcessorSlotChain> newMap = new HashMap<ResourceWrapper, ProcessorSlotChain>(
chainMap.size() + 1);
newMap.putAll(chainMap);
newMap.put(resourceWrapper, chain);
chainMap = newMap;
}
}
} return chain;
}该方法主要就是根据资源获取到对应的ProcessorSlotChain，这里通过一个HashMap将资源和ProcessorSlotChain的关系缓存起来了，如果根据资源没有在缓存中找到ProcessorSlotChain，则创建一个新的ProcessorSlotChain。而ProcessorSlotChain则是具体限流、降级等操作的入口。在sentinel中定义了一系列的功能插槽(Solt)，目前有7个：NodeSelectorSlot、ClusterBuilderSlot、LogSlot、StatisticSlot、SystemSlot、AuthoritySlot、FlowSlot、DegradeSlot。每个插槽对应不同的功能，比如FlowSlot负责流量控制、DegradeSlot用来做熔断降级，具体的可以查看官方文档，每个资源可以对应一个或多个Solt。ProcessorSlotChain主要就是针对资源调用具体插槽的逻辑，将一个或多个插槽泡拼装成一条链，在执行完当期插槽逻辑的之后，出发下一个插槽的逻辑，直到整条链调用完成。
SlotChainProvider.newSlotChain()的具体逻辑如下：
private static volatile SlotChainBuilder builder = null;private static final ServiceLoader<SlotChainBuilder> LOADER = ServiceLoader.load(SlotChainBuilder.class);public static ProcessorSlotChain newSlotChain() { if (builder != null) { return builder.build();
}
resolveSlotChainBuilder(); if (builder == null) {
RecordLog.warn("[SlotChainProvider] Wrong state when resolving slot chain builder, using default");
builder = new DefaultSlotChainBuilder();
} return builder.build();
}这里引入了SPI的概念，在sentinel-core模块的resource/META-INF/services目录下，有一个名为com.alibaba.csp.sentinel.slotchain.SlotChainBuilder的文件，文件内容如下：
# Default slot chain buildercom.alibaba.csp.sentinel.slots.DefaultSlotChainBuilder
即，这里引用的是DefaultSlotChainBuilder，同时这也说明我们可以自定义SlotChainBuilder实现。
public class DefaultSlotChainBuilder implements SlotChainBuilder { @Override
public ProcessorSlotChain build() {
ProcessorSlotChain chain = new DefaultProcessorSlotChain();
chain.addLast(new NodeSelectorSlot());
chain.addLast(new ClusterBuilderSlot());
chain.addLast(new LogSlot());
chain.addLast(new StatisticSlot());
chain.addLast(new SystemSlot());
chain.addLast(new AuthoritySlot());
chain.addLast(new FlowSlot());
chain.addLast(new DegradeSlot()); return chain;
}
}DefaultProcessorSlotChain 中的部分代码
public class DefaultProcessorSlotChain extends ProcessorSlotChain {
AbstractLinkedProcessorSlot<?> first = new AbstractLinkedProcessorSlot<Object>() { @Override
public void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count, Object... args)
throws Throwable { super.fireEntry(context, resourceWrapper, t, count, args);
} @Override
public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) { super.fireExit(context, resourceWrapper, count, args);
}
};
AbstractLinkedProcessorSlot<?> end = first; @Override
public void addFirst(AbstractLinkedProcessorSlot<?> protocolProcessor) {
protocolProcessor.setNext(first.getNext());
first.setNext(protocolProcessor); if (end == first) {
end = protocolProcessor;
}
} @Override
public void addLast(AbstractLinkedProcessorSlot<?> protocolProcessor) {
end.setNext(protocolProcessor);
end = protocolProcessor;
}
}主要就是将不同的插槽拼装成一条链路，addFirst表示加在链表的头部，主要通过改变first的next指向来实现；addLast表示加在链表的尾部，主要通过改变end的next指向来实现，如果不是很理解，在纸上比划比划就很清楚了。
ProcessorSlotChain执行
以上是有关于ProcessorSlotChain的生成逻辑，接下来看看ProcessorSlotChain的执行逻辑，继续回到Ctsph中的entry方法，在上面已经粘贴过一次，这里省略部分非关键代码：
public Entry entry(ResourceWrapper resourceWrapper, int count, Object... args) throws BlockException {
ProcessorSlot<Object> chain = lookProcessChain(resourceWrapper); // 如果chain为空，说明资源数已经超过sentinel设置的最带值了，默认是6000
if (chain == null) { return new CtEntry(resourceWrapper, null, context);
}
Entry e = new CtEntry(resourceWrapper, chain, context); try { // ProcessorSlotChain执行入口
chain.entry(context, resourceWrapper, null, count, args);
} catch (BlockException e1) {
e.exit(count, args); throw e1;
} catch (Throwable e1) { // This should not happen, unless there are errors existing in Sentinel internal.
RecordLog.info("Sentinel unexpected exception", e1);
} return e;
}不难发现，入口在chain.entry(context, resourceWrapper, null, count, args)，从上面的ProcessorSlotChain生成逻辑可以发现，生成的是DefaultProcessorSlotChain，所以主要关注DefaultProcessorSlotChain的entry方法
// DefaultProcessorSlotChain.javapublic void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count, Object... args)
throws Throwable {
first.transformEntry(context, resourceWrapper, t, count, args);
}// AbstractLinkedProcessorSlot.javavoid transformEntry(Context context, ResourceWrapper resourceWrapper, Object o, int count, Object... args)
throws Throwable {
T t = (T)o;
entry(context, resourceWrapper, t, count, args);
}//DefaultProcessorSlotChain.javapublic void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count, Object... args)
throws Throwable { super.fireEntry(context, resourceWrapper, t, count, args);
}// AbstractLinkedProcessorSlot.javapublic void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, Object... args)
throws Throwable { // 这里的next其实就是指具体的插槽实现了
if (next != null) {
next.transformEntry(context, resourceWrapper, obj, count, args);
}
}最关键的部分其实就在fireEntry方法中，这里的next其实就是指具体的插槽实现，比如这里以FlowSlot为例：
public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count, Object... args)
throws Throwable { // FlowSlot具体的插槽逻辑
checkFlow(resourceWrapper, context, node, count);
// 通过调用AbstractLinkedProcessorSlot的fireEntry方法，用来触发下一个插槽逻辑的调用
fireEntry(context, resourceWrapper, node, count, args);
}其实这就是插槽链的调用，比如SpringAOP中的Intercepterl链、Mybatis中的plugin链路，虽然具体的实现方式不同，但是目的都是一样的：执行完整条链上的逻辑。
上面的调用都是理想的情况，即：所有的请求都通过，没有被限制的情况。如果请求被拒绝，该怎么处理？这里还是以FlowSlot为例：
public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count, Object... args)
throws Throwable {
checkFlow(resourceWrapper, context, node, count);
fireEntry(context, resourceWrapper, node, count, args);
}void checkFlow(ResourceWrapper resource, Context context, DefaultNode node, int count) throws BlockException { // Flow rule map cannot be null.
Map<String, List<FlowRule>> flowRules = FlowRuleManager.getFlowRules();
List<FlowRule> rules = flowRules.get(resource.getName()); if (rules != null) { for (FlowRule rule : rules) { if (!canPassCheck(rule, context, node, count)) { throw new FlowException(rule.getLimitApp());
}
}
}
}可以看到，如果请求被拒绝，即：被限流了，则抛出BlockException异常，在外层如果捕获到BlockException异常，则在里面处理对应的逻辑。
sentinel-dashboard
sentinel-dashboard是sentinel的轻量级控制台，该控制台主要提供两个功能：监控、配置。即：针对资源的监控和针对资源的配置，比如：可以配置一些规则。
sentinel-dashboard是基于spring-boot2，所以直接启动DashboardApplication就可以了，当然也可以以jar包的方式启动，启动之后的界面效果如下：
没错，什么都没有，因为这时候没有可监控的应用。
接入到sentinel-dashboard的流程也很简单，新建一个应用， 添加以下依赖
<!-- sentinel-dashboard --><dependency> <groupId>com.alibaba.csp</groupId> <artifactId>sentinel-transport-simple-http</artifactId> <version>1.4.0-SNAPSHOT</version></dependency>
以下是测试代码，其实就是源码中的demo，这里直接搬过来
package com.hand.sxy.sentinel;import java.util.ArrayList;import java.util.List;import java.util.Random;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;import com.alibaba.csp.sentinel.util.TimeUtil;import com.alibaba.csp.sentinel.Entry;import com.alibaba.csp.sentinel.SphU;import com.alibaba.csp.sentinel.slots.block.BlockException;import com.alibaba.csp.sentinel.slots.block.RuleConstant;import com.alibaba.csp.sentinel.slots.block.flow.FlowRule;import com.alibaba.csp.sentinel.slots.block.flow.FlowRuleManager;public class FlowQps { private static final String KEY = "abc"; private static AtomicInteger pass = new AtomicInteger(); private static AtomicInteger block = new AtomicInteger(); private static AtomicInteger total = new AtomicInteger(); private static volatile boolean stop = false; private static final int threadCount = 32; private static int seconds = 600000 + 40; public static void main(String[] args) throws Exception {
initFlowQpsRule();
tick(); // first make the system run on a very low condition
simulateTraffic();
System.out.println("===== begin to do flow control");
System.out.println("only 20 requests per second can pass");
} private static void initFlowQpsRule() {
List<FlowRule> rules = new ArrayList<FlowRule>();
FlowRule rule1 = new FlowRule();
rule1.setResource(KEY); // set limit qps to 20
rule1.setCount(20);
rule1.setGrade(RuleConstant.FLOW_GRADE_QPS);
rule1.setLimitApp("default");
rules.add(rule1);
FlowRuleManager.loadRules(rules);
} private static void simulateTraffic() { for (int i = 0; i < threadCount; i++) {
Thread t = new Thread(new RunTask());
t.setName("simulate-traffic-Task");
t.start();
}
} private static void tick() {
Thread timer = new Thread(new TimerTask());
timer.setName("sentinel-timer-task");
timer.start();
} static class TimerTask implements Runnable { @Override
public void run() { long start = System.currentTimeMillis();
System.out.println("begin to statistic!!!"); long oldTotal = 0; long oldPass = 0; long oldBlock = 0; while (!stop) { try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
} long globalTotal = total.get(); long oneSecondTotal = globalTotal - oldTotal;
oldTotal = globalTotal; long globalPass = pass.get(); long oneSecondPass = globalPass - oldPass;
oldPass = globalPass; long globalBlock = block.get(); long oneSecondBlock = globalBlock - oldBlock;
oldBlock = globalBlock;
System.out.println(seconds + " send qps is: " + oneSecondTotal);
System.out.println(TimeUtil.currentTimeMillis() + ", total:" + oneSecondTotal
+ ", pass:" + oneSecondPass
+ ", block:" + oneSecondBlock); if (seconds-- <= 0) {
stop = true;
}
} long cost = System.currentTimeMillis() - start;
System.out.println("time cost: " + cost + " ms");
System.out.println("total:" + total.get() + ", pass:" + pass.get()
+ ", block:" + block.get());
System.exit(0);
}
} static class RunTask implements Runnable { @Override
public void run() { while (!stop) {
Entry entry = null; try {
entry = SphU.entry(KEY); // token acquired, means pass
pass.addAndGet(1);
} catch (BlockException e1) {
block.incrementAndGet();
} catch (Exception e2) { // biz exception
} finally {
total.incrementAndGet(); if (entry != null) {
entry.exit();
}
}
Random random2 = new Random(); try {
TimeUnit.MILLISECONDS.sleep(random2.nextInt(50));
} catch (InterruptedException e) { // ignore
}
}
}
}
}启动的时候，添加以下参数：
-Djava.net.preferIPv4Stack=true-Dcsp.sentinel.dashboard.server=localhost:8080 -Dcsp.sentinel.api.port=8720 -Dproject.name=我的APP
启动之后，刷新界面，查看效果
有关于控制台的一些功能就不过多介绍了，有兴趣可以自己看看。
Dubbo适配
看官方文档，除了dubbo适配，文档上还有与其它主流框架适配的介绍。dubbo适配主要是涉及到两个Filtter：SentinelDubboConsumerFilter、SentinelDubboProviderFilter。从名字上也可以看出来，SentinelDubboConsumerFilter主要是限制调用方请求；SentinelDubboProviderFilter主要就是限制提供方提供。有关于这两个应用场景，推荐看看dubbo的官方文档，上面有详细的说明，并且还列举了比较好的例子，例如：
作者：spilledyear
链接：https://www.jianshu.com/p/ed57014e1abb
这篇关于Sentinel的文章就介绍到这儿，希望我们推荐的文章对大家有所帮助，也希望大家多多支持为之网！
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