1.什么是Dag？
有向无环图(Directed Acyclic Graph)，简称DAG，是一种有向图，其中没有从节点出发经过若干条边后再回到该节点的路径。换句话说，DAG中不存在环路。这种数据结构常用于表示并解决具有依赖关系的问题。
DAG的特性
首先，DAG中的节点可以有入度和出度。节点的入度是指指向该节点的边的数量，而节点的出度是指由该节点指向其他节点的边的数量。在DAG中，节点的入度可以是0或正整数，而出度可以是0或正整数，但不能同时为负数。
DAG的另一个重要性质是存在一个或多个拓扑排序。拓扑排序是DAG中节点的线性排列，满足任意一条有向边的起点在排序中都位于终点之前。可以使用深度优先搜索(DFS)或宽度优先搜索(BFS)算法来生成拓扑排序。
DAG的应用
任务调度
编译器优化
数据流分析
电路设计
2.如何加速Spring Bean初始化？
在Spring框架中进行DAG（有向无环图）分析以实现并行初始化，可以有效提升应用程序启动的性能。通常情况下，Spring应用程序的Bean是按依赖顺序初始化的，而通过DAG分析可以识别出哪些Bean之间没有依赖关系，并行初始化这些Bean可以减少启动时间。以下是实现思路：
1. 识别依赖关系，构建DAG
首先需要识别Spring Bean之间的依赖关系。可以通过@DependsOn注解、构造器注入或@Autowired等方式获取Bean依赖。具体步骤：
遍历Spring上下文中的所有Bean定义。
根据Bean的依赖关系构建DAG，节点代表Bean，边表示依赖关系。
Spring的ApplicationContext提供了getBeanDefinitionNames()方法可以列出所有的Bean，通过BeanDefinition可以分析出依赖。
2. 拓扑排序
通过拓扑排序（Topological Sorting）对DAG进行排序，以确保Bean按依赖顺序初始化。拓扑排序可以确定哪些Bean可以并行初始化，哪些Bean必须在某些Bean之后初始化。 使用算法如Kahn’s Algorithm或DFS找到所有没有依赖的Bean（入度为0的节点），这些节点可以并行初始化。
3. 并行初始化Bean
在完成拓扑排序后，使用多线程来并行初始化可以同时启动的Bean。可以使用Java的ExecutorService或类似的线程池机制来管理并发的Bean初始化过程。 步骤：
针对所有入度为0的节点，启动一个线程来初始化它们。
当某个Bean初始化完成后，减少它所依赖的其他Bean的入度值。
当某个Bean的入度为0时，可以在另一个线程中启动它的初始化。
4. Spring Integration
可以通过BeanFactoryPostProcessor或ApplicationContextInitializer来挂钩到Spring的初始化流程中，分析Bean之间的依赖关系，并将并行化初始化逻辑集成到Spring容器的启动过程中。 具体方法：
实现
BeanFactoryPostProcessor，在Bean初始化之前分析Bean的依赖并构建DAG。在Bean初始化阶段，使用多线程并行处理独立的Bean。
3.代码工程
整体的依赖关系如下：
实验目标
实现自定义Bean并行化加载
pom.xml
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>3.2.1</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>dag</artifactId> <properties> <maven.compiler.source>17</maven.compiler.source> <maven.compiler.target>17</maven.compiler.target> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-autoconfigure</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.jgrapht</groupId> <artifactId>jgrapht-core</artifactId> <version>1.5.1</version> </dependency> </dependencies> <build> <pluginManagement> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.8.1</version> <configuration> <fork>true</fork> <failOnError>false</failOnError> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-surefire-plugin</artifactId> <version>2.22.2</version> <configuration> <forkCount>0</forkCount> <failIfNoTests>false</failIfNoTests> </configuration> </plugin> </plugins> </pluginManagement> </build> </project>
Bean初始化
package com.et.config;
import org.jgrapht.graph.DefaultEdge;
import org.jgrapht.graph.DirectedAcyclicGraph;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;
import java.util.*;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.stream.Collectors;
@Component
public class DAGBeanInitializer implements BeanFactoryPostProcessor {
private final ExecutorService executorService = Executors.newFixedThreadPool(10);
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
Map<String, BeanDefinition> beanDefinitionMap = new HashMap<>();
for (String beanName : beanFactory.getBeanDefinitionNames()) {
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
beanDefinitionMap.put(beanName, beanDefinition);
}
// build DAG
DirectedAcyclicGraph<String, DefaultEdge> dag = buildDAG(beanDefinitionMap,beanFactory);
// bean layers
List<Set<String>> layers = getBeansByLayer(dag);
System.out.println("layers:"+layers);
// init bean by layers
initializeBeansInLayers(layers, beanFactory);
}
// DAG Bean
private DirectedAcyclicGraph<String, DefaultEdge> buildDAG(Map<String, BeanDefinition> beanDefinitionMap, ConfigurableListableBeanFactory beanFactory) {
DependencyResolver resolver = new DependencyResolver(beanFactory);
DirectedAcyclicGraph<String, DefaultEdge> dag = new DirectedAcyclicGraph<>(DefaultEdge.class);
for (String beanName : beanDefinitionMap.keySet()) {
if(shouldLoadBean(beanName)) {
dag.addVertex(beanName);
String[] dependencies = beanDefinitionMap.get(beanName).getDependsOn();
if (dependencies != null) {
for (String dependency : dependencies) {
dag.addEdge(dependency, beanName);
}
}
// get @Autowired dependencies
Set<String> autowireDependencies = resolver.getAllDependencies(beanName);
for (String autowireDependency : autowireDependencies) {
// convert beanName
String autowireBeanName = convertToBeanName(autowireDependency);
dag.addVertex(autowireBeanName);
dag.addEdge(autowireBeanName, beanName);
}
}
}
return dag;
}
private String convertToBeanName(String className) {
String simpleName = className.substring(className.lastIndexOf('.') + 1);
return Character.toLowerCase(simpleName.charAt(0)) + simpleName.substring(1);
}
private List<Set<String>> getBeansByLayer(DirectedAcyclicGraph<String,DefaultEdge> dag) {
List<Set<String>> layers = new ArrayList<>();
Map<String, Integer> inDegree = new HashMap<>();
Queue<String> queue = new LinkedList<>();
// init all nodes degree
for (String vertex : dag) {
int degree = dag.inDegreeOf(vertex);
inDegree.put(vertex, degree);
if (degree == 0) {
queue.offer(vertex); //zero degree as the first layer
}
}
// BFS process everyLayers
while (!queue.isEmpty()) {
Set<String> currentLayer = new HashSet<>();
int size = queue.size();
for (int i = 0; i < size; i++) {
String currentBean = queue.poll();
currentLayer.add(currentBean);
// iterator layers
for (String successor : getSuccessors(dag,currentBean)) {
inDegree.put(successor, inDegree.get(successor) - 1);
if (inDegree.get(successor) == 0) {
queue.offer(successor); // add next layer when the degress is zero
}
}
}
layers.add(currentLayer);
}
return layers;
}
// get next node
private Set<String> getSuccessors(DirectedAcyclicGraph<String, DefaultEdge> dag, String vertex) {
// get outgoingEdges
Set<DefaultEdge> outgoingEdges = dag.outgoingEdgesOf(vertex);
// find the next node
return outgoingEdges.stream()
.map(edge -> dag.getEdgeTarget(edge))
.collect(Collectors.toSet());
}
// init beans by layer
private void initializeBeansInLayers(List<Set<String>> layers, ConfigurableListableBeanFactory beanFactory) {
for (Set<String> layer : layers) {
// Beans of the same layer can be initialized in parallel
List<CompletableFuture<Void>> futures = new ArrayList<>();
for (String beanName : layer) {
// only load beans that wrote by yourself
if (shouldLoadBean(beanName)) {
CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
try {
beanFactory.getBean(beanName); // init Bean
} catch (Exception e) {
System.err.println("Failed to initialize bean: " + beanName);
e.printStackTrace();
}
}, executorService);
futures.add(future);
}
}
//Wait for all beans in the current layer to be initialized before initializing the next layer.
CompletableFuture<Void> allOf = CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]));
allOf.join(); // make sure to be done on current layer
}
}
private boolean shouldLoadBean(String beanName) {
return beanName.startsWith("helloWorldController")
||beanName.startsWith("serviceOne")
||beanName.startsWith("serviceTwo")
||beanName.startsWith("serviceThree");
}
}获取bean@Autowired依赖
package com.et.config;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.lang.reflect.Field;
import java.util.HashSet;
import java.util.Set;
@Component
public class DependencyResolver {
private final ConfigurableListableBeanFactory beanFactory;
@Autowired
public DependencyResolver(ConfigurableListableBeanFactory beanFactory) {
this.beanFactory = beanFactory;
}
public Set<String> getAllDependencies(String beanName) {
Set<String> dependencies = new HashSet<>();
// get Bean definite
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
// reflect
try {
Class<?> beanClass = Class.forName(beanDefinition.getBeanClassName());
Field[] fields = beanClass.getDeclaredFields();
for (Field field : fields) {
if (field.isAnnotationPresent(Autowired.class)) {
dependencies.add(field.getType().getName());
}
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return dependencies;
}
}controller
package com.et.controller;
import com.et.service.ServiceTwo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.et.service.*;
import java.util.HashMap;
import java.util.Map;
@RestController
public class HelloWorldController {
@Autowired
ServiceOne ServiceOne;
@Autowired
ServiceTwo ServiceTwo;
@RequestMapping("/hello")
public Map<String, Object> showHelloWorld(){
Map<String, Object> map = new HashMap<>();
map.put("msg", "HelloWorld");
return map;
}
}service
package com.et.service;
import org.springframework.stereotype.Service;
/**
* @author liuhaihua
* @version 1.0
* @ClassName ServiceOne
* @Description todo
* @date 2024/09/20/ 14:01
*/
@Service
public class ServiceOne {
private void sayhi(){
System.out.println("this is service one sayhi");
}
}package com.et.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
/**
* @author liuhaihua
* @version 1.0
* @ClassName ServiceOne
* @Description todo
* @date 2024/09/20/ 14:01
*/
@Service
public class ServiceTwo {
@Autowired
ServiceThree serviceThree;
private void sayhi(){
System.out.println("this is service two sayhi");
}
}package com.et.service;
import org.springframework.stereotype.Service;
/**
* @author liuhaihua
* @version 1.0
* @ClassName ServiceOne
* @Description todo
* @date 2024/09/20/ 14:01
*/
@Service
public class ServiceThree {
private void sayhi(){
System.out.println("this is service three sayhi");
}
}只是一些关键代码，所有代码请参见下面代码仓库
代码仓库
https://github.com/Harries/springboot-demo(dag)
4.测试
启动Spring Boot工程，查看bean加载顺序如下
2024-09-20T15:51:27.081+08:00 INFO 33188 --- [ main] com.et.DemoApplication : Starting DemoApplication using Java 17.0.9 with PID 33188 (D:\IdeaProjects\ETFramework\dag\target\classes started by Dell in D:\IdeaProjects\ETFramework) 2024-09-20T15:51:27.085+08:00 INFO 33188 --- [ main] com.et.DemoApplication : No active profile set, falling back to 1 default profile: "default"layers:[[serviceOne, serviceThree], [serviceTwo], [helloWorldController]] 2024-09-20T15:51:28.286+08:00 INFO 33188 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port 8088 (http)2024-09-20T15:51:28.297+08:00 INFO 33188 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2024-09-20T15:51:28.297+08:00 INFO 33188 --- [ main] o.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/10.1.17]2024-09-20T15:51:28.373+08:00 INFO 33188 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2024-09-20T15:51:28.374+08:00 INFO 33188 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1198 ms 2024-09-20T15:51:28.725+08:00 INFO 33188 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port 8088 (http) with context path '' 2024-09-20T15:51:28.732+08:00 INFO 33188 --- [ main] com.et.DemoApplication
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