Java虚拟线程（一）

2023下半年，Java 21开始正式支持虚拟线程 Virtual Thread
本文先介绍几种使用方法。

1. 直接创建虚拟线程并运行

Thread vt = Thread.startVirtualThread(new Runnable() {
     @Override
     public void run() {
        System.out.println("hello virtual thread 1");
     }
});

2. 创建虚拟线程但不运行，之后手动运行

vt = Thread.ofVirtual().unstarted(() -> {
    System.out.println("hello virtual thread 2");
});
vt.start();

3. 通过虚拟线程ThreadFactory创建

ThreadFactory threadFactory = Thread.ofVirtual().name("my-virtual-thread-").factory();
vt = threadFactory.newThread(() -> {
     System.out.println("hello virtual thread 3");
});
vt.start();

4. 使用Executors.newVirtualThreadPerTaskExecutor ExecutorService创建虚拟线程

ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
executorService.submit(() -> {
     System.out.println("hello virtual thread 4");
});

5. 用普通的Executors.newThreadPerTaskExecutor ExecutorService、配合虚拟线程工厂，创建虚拟线程

executorService = Executors.newThreadPerTaskExecutor(threadFactory);
executorService.submit(() -> {
     System.out.println("hello virtual thread 5");
});

虚拟线程的世界没有线程池

上面4、5的例子虽然用Executors创建了ExecutorService，但跟之前直觉不一样，严格说并不是创建了两个线程池。这俩都属于“one Thread Per Task”的。
虚拟线程非常轻量，创建的开销很小，不需要池化进行复用，用的时候直接创建，然后等GC回收就行了，非常暴力！
但线程池的作用不只是复用线程，也有隔离和限制并发的作用，在虚拟线程的情况下，这个通常可以用信号量Semaphore来解决，下一篇我们介绍。

完整演示代码

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

public class VThreadTest {
    public static void main(String[] args) throws InterruptedException {
        //1. 直接创建虚拟线程并运行
        Thread vt = Thread.startVirtualThread(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello virtual thread 1");
            }
        });
        TimeUnit.SECONDS.sleep(1);

        //2. 创建虚拟线程但不运行，之后手动运行
        vt = Thread.ofVirtual().unstarted(() -> {
            System.out.println("hello virtual thread 2");
        });
        vt.start();
        TimeUnit.SECONDS.sleep(1);

        //3. 通过虚拟线程ThreadFactory创建
        ThreadFactory threadFactory = Thread.ofVirtual().name("my-virtual-thread-").factory();
        vt = threadFactory.newThread(() -> {
            System.out.println("hello virtual thread 3");
        });
        vt.start();
        TimeUnit.SECONDS.sleep(1);

        //4. 使用newVirtualThreadPerTaskExecutor ExecutorService创建虚拟线程
        ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
        executorService.submit(() -> {
            System.out.println("hello virtual thread 4");
        });
        TimeUnit.SECONDS.sleep(1);

        //5. 用普通的newThreadPerTaskExecutor ExecutorService、配合虚拟线程工厂，创建虚拟线程
        executorService = Executors.newThreadPerTaskExecutor(threadFactory);
        executorService.submit(() -> {
            System.out.println("hello virtual thread 5");
        });
        TimeUnit.SECONDS.sleep(1);

    }
}

运行结果：

hello virtual thread 1
hello virtual thread 2
hello virtual thread 3
hello virtual thread 4
hello virtual thread 5