spring boot 3 + 虚拟线程 + MDC traceId

虚拟线程（Virtual Thread）也称协程或纤程，是一种轻量级的线程实现，与传统的线程以及操作系统级别的线程（也称为平台线程）相比，它的创建开销更小、资源利用率更高，是 Java 并发编程领域的一项重要创新。

PS：虚拟线程正式发布于 Java 长期支持版（Long Term Suort，LTS）Java 21（也就是 JDK 21）。

虚拟线程是一种在 Java 虚拟机（JVM）层面实现的逻辑线程，不直接和操作系统的物理线程一一对应，因此它可以减少上下文切换所带来的性能开销。

1 开启虚拟线程

spring boot 3中开启虚拟线程，可在yaml配置文件中添加如下配置：

spring:threads:virtual:enabled: true

此时，所有请求tomcat都会使用使用虚拟线程来处理，在controller中打印当前线程：

VirtualThread[#69,tomcat-handler-0]/runnable@ForkJoinPool-1-worker-1

如果需要@Async注解也支持虚拟线程，需要添加如下配置：

@EnableAsync注解，我这里放到了启动类上的

@Configuration
//保证是在开启虚拟线程的情况下，再启用这个配置
@ConditionalOnProperty(prefix = "spring.threads.virtual", name = "enabled", havingValue = "true")
public class ThreadVirtualConfig {/*** Async 注解支持** @return*/@Beanpublic AsyncTaskExecutor taskExecutor() {//指定线程名称为virtual-async#，如果不需要指定，可直接 Executors.newVirtualThreadPerTaskExecutor()return new TaskExecutorAdapter(Executors.newThreadPerTaskExecutor(Thread.ofVirtual().name("virtual-async#", 1).factory()));}/*** 让tomcat使用虚拟线程来处理请求* 如果配置 spring.threads.virtual.enabled = true 配置没生效的话，可开启如下bean配置* 我这里spring boot 3.3.4 是生效的** @return*//*@Beanpublic TomcatProtocolHandlerCustomizer<?> protocolHandlerCustomizer() {return protocolHandler -> protocolHandler.setExecutor(Executors.newVirtualThreadPerTaskExecutor());}*/
}

此时在使用@Async注解的方法中打印当前线程：

VirtualThread[#76,virtual-async#1]/runnable@ForkJoinPool-1-worker-3

虚拟线程创建有以下四种方式：

Thread.startVirtualThread(Runnable task)：创建虚拟线程，并直接启动执行任务
Thread.startVirtualThread(() -> {System.out.println("Do virtual thread.");
});
Thread.ofVirtual().unstarted(Runnable task)：只创建虚拟线程，但不直接启动（创建之后通过 start 启动）
Thread vt = Thread.ofVirtual().unstarted(()->{System.out.println("Do virtual thread.");
});
vt.start();
Thread.ofVirtual().factory()：先创建虚拟线程工厂，然后再使用工厂创建虚拟线程，之后再调用 start() 方法进行执行
ThreadFactory tf = Thread.ofVirtual().factory();
Thread vt = tf.newThread(()->{System.out.println("Do virtual thread.");
});
vt.start();
Executors.newVirtualThreadPerTaskExecutor()：创建虚拟线程
ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
executor.submit(()->{System.out.println("Do virtual thread.");
});

2 生成MDC traceId

分成两步走，主线程的通过拦截器设置，@Async创建的子线程通过创建时自动复制过去

2.1 主线程

拦截器 LogTraceIdInterceptor.java

public class LogTraceIdInterceptor implements HandlerInterceptor {private static final String TRACE_ID = "TRACE_ID";@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {String tid = UUID.randomUUID().toString().replace("-", "");if (StringUtils.hasText(request.getHeader(TRACE_ID))) {tid = request.getHeader(TRACE_ID);}MDC.put(TRACE_ID, tid);return true;}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {MDC.remove(TRACE_ID);}
}

配置生效

@Configuration
public class WebConfigurerAdapter implements WebMvcConfigurer {@Beanpublic LogTraceIdInterceptor logTraceIdInterceptor() {return new LogTraceIdInterceptor();}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(logTraceIdInterceptor());}
}

2.2 子线程

CustomVirtualThreadTaskExecutor.java

public class CustomVirtualThreadTaskExecutor extends TaskExecutorAdapter {public CustomVirtualThreadTaskExecutor() {super(Executors.newThreadPerTaskExecutor(Thread.ofVirtual().name("virtual-async#", 1).factory()));}@Overridepublic void execute(@NotNull Runnable task) {super.execute(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));}@Overridepublic <T> Future<T> submit(@NotNull Callable<T> task) {return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));}@Overridepublic Future<?> submit(@NotNull Runnable task) {return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));}
}

ThreadMdcUtil.java

public final class ThreadMdcUtil {private static final String TRACE_ID = "TRACE_ID";private ThreadMdcUtil(){}/*** 获取唯一性标识** @return*/public static String generateTraceId() {return UUID.randomUUID().toString();}public static void setTraceIdIfAbsent() {if (MDC.get(TRACE_ID) == null) {MDC.put(TRACE_ID, generateTraceId());}}/*** 用于父线程向线程池中提交任务时，将自身MDC中的数据复制给子线程** @param callable* @param context* @param <T>* @return*/public static <T> Callable<T> wrap(final Callable<T> callable, final Map<String, String> context) {return () -> {if (context == null) {MDC.clear();} else {MDC.setContextMap(context);}setTraceIdIfAbsent();try {return callable.call();} finally {MDC.clear();}};}/*** 用于父线程向线程池中提交任务时，将自身MDC中的数据复制给子线程** @param runnable* @param context* @return*/public static Runnable wrap(final Runnable runnable, final Map<String, String> context) {return () -> {if (context == null) {MDC.clear();} else {MDC.setContextMap(context);}setTraceIdIfAbsent();try {runnable.run();} finally {MDC.clear();}};}
}

将此前的ThreadVirtualConfig配置调整为如下：

@Configuration
@ConditionalOnProperty(prefix = "spring.threads.virtual", name = "enabled", havingValue = "true")
public class ThreadVirtualConfig {/*** Async 注解支持** @return*/@Beanpublic Executor taskExecutor() {return new CustomVirtualThreadTaskExecutor();}
}