Java 协程：Loom Project 实战

Loom Project 是 OpenJDK 在2018年创建的协程方案，是在JVM层实现的有栈协程。到2020年9月为止，该项目还没有明确发布日期，目前可以下载 Early-Access 版本进行试用。

和传统的Java线程相比，loom协程占用内存、CPU资源更少，支持百万数量级的并发。

main.java

import java.time.Instant;
import java.util.List;
import java.util.concurrent.*;

public class main {

    public static void main(String[] args) throws Exception {

        //  ------------------------  Thread API -------------------------------------------------------

        // The following uses a static factory method to start a virtual thread.
        // It invokes the join method to wait for the thread to terminate.
        Thread thread = Thread.startVirtualThread(() -> System.out.println("startVirtualThread"));
        thread.join();

        // The Thread.Builder API can also be used to create virtual threads that are configured at build time.
        // The first snippet below creates an un-started thread.
        // The second snippet creates and starts a thread with name "Thread-builder".
        Thread thread1 = Thread.builder().virtual().task(() -> System.out.println("Thread.builder build")).build();
        thread1.start();
        thread1.join();

        Thread thread2 = Thread.builder()
                .virtual()
                .name("Thread-builder")
                .task(() -> System.out.println("Thread.builder start, thread name: " + Thread.currentThread().getName()))
                .start();
        thread2.join();

        // The Thread.Builder API can also be used to create a ThreadFactory.
        // The ThreadFactory created by the following snippet will create virtual threads
        // named "worker-0", "worker-1", "worker-2", ...
        ThreadFactory factory = Thread.builder().virtual().name("worker-", 0).factory();
        Thread thread3 = factory.newThread(() ->
                System.out.println("ThreadFactory thread: " + Thread.currentThread().getName()));
        thread3.start();
        thread3.join();
        thread3 = factory.newThread(() ->
                System.out.println("ThreadFactory thread: " + Thread.currentThread().getName()));
        thread3.start();
        thread3.join();
        thread3 = factory.newThread(() ->
                System.out.println("ThreadFactory thread: " + Thread.currentThread().getName()));
        thread3.start();
        thread3.join();

        // ------------------------ ExecutorService API ---------------------------------------------------

        // The following creates an ExecutorService that runs each task in its own virtual thread.
        // The example uses the try-with-resources construct to ensure that the ExecutorService is shutdown
        // and that the two tasks (each run in its own virtual thread) complete before continuing.
        try (ExecutorService executor = Executors.newVirtualThreadExecutor()) {
            executor.execute(() -> System.out.println("newVirtualThreadExecutor 1"));
            executor.execute(() -> System.out.println("newVirtualThreadExecutor 2"));
        }

        // The example below runs three tasks and selects the result of the first task to complete.
        // The remaining tasks are cancelled, which causes the virtual threads running them to be interrupted.
        try (ExecutorService executor = Executors.newVirtualThreadExecutor()) {
            Callable<String> task1 = () -> "foo";
            Callable<String> task2 = () -> "bar";
            Callable<String> task3 = () -> "baz";
            String result = executor.invokeAny(List.of(task1, task2, task3));
            System.out.println("invokeAny result: " + result);
        }

        // This following example uses submitTasks to submit three value returning tasks.
        // It uses the CompletableFuture.completed method to obtain a stream that is lazily populated as the tasks complete.
        try (ExecutorService executor = Executors.newVirtualThreadExecutor()) {
            Callable<String> task1 = () -> "completed foo";
            Callable<String> task2 = () -> "completed bar";
            Callable<String> task3 = () -> "completed baz";
            List<CompletableFuture<String>> cfs = executor.submitTasks(List.of(task1, task2, task3));
            CompletableFuture.completed(cfs)
                    .map(CompletableFuture::join)
                    .forEach(System.out::println);
        }

        // The following creates an ExecutorService that runs each task in its own virtual thread with a deadline.
        // If the deadline expires before the executor has terminated then the thread executing this code
        // will be interrupted and any tasks running will be cancelled. (which causes the virtual thread to be interrupted).
        Instant deadline = Instant.now().plusSeconds(1);
        try (ExecutorService executor = Executors.newVirtualThreadExecutor().withDeadline(deadline)) {
            executor.submit(() -> {
                try {
                    Thread.sleep(500);
                    System.out.println("withDeadline 500");
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            });

            executor.submit(() -> {
                try {
                    Thread.sleep(800);
                    System.out.println("withDeadline 800");
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            });

            executor.submit(() -> {
                try {
                    Thread.sleep(1200);
                    System.out.println("withDeadline 1200");
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            });
        }
    }
}

输出：

startVirtualThread

Thread.builder build
Thread.builder start, thread name: Thread-builder

ThreadFactory thread: worker-0
ThreadFactory thread: worker-1
ThreadFactory thread: worker-2

newVirtualThreadExecutor 1
newVirtualThreadExecutor 2

invokeAny result: foo

completed foo
completed bar
completed baz

withDeadline 500
withDeadline 800

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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.target>16</maven.compiler.target>
        <maven.compiler.source>16</maven.compiler.source>
    </properties>

</project>

loom jdk Early-Access 下载

loom 官方介绍及待完善部分