有没有办法判断虚拟线程在哪个载体线程上运行？

Question

我第一次玩 Project Loom 并且我有一些代码

try (var executor = Executors.newVirtualThreadExecutor()) {
    IntStream.range(0, 16).forEach(i -> {
        System.out.println("i = " + i + ", Thread ID = " + Thread.currentThread());
        executor.submit(() -> {
            System.out.println("Thread ID = " + Thread.currentThread());
        });
    });
}

输出像

Thread ID = VirtualThread[#37]/runnable@ForkJoinPool-1-worker-4
Thread ID = VirtualThread[#33]/runnable@ForkJoinPool-1-worker-5
i = 9, Thread ID = Thread[#1,main,5,main]
Thread ID = VirtualThread[#43]/runnable@ForkJoinPool-1-worker-9
Thread ID = VirtualThread[#46]/runnable@ForkJoinPool-1-worker-11
i = 10, Thread ID = Thread[#1,main,5,main]
i = 11, Thread ID = Thread[#1,main,5,main]

有没有办法告诉我每个虚拟线程在哪个载体线程上运行？

ForkJoinPool-1-worker-11代表一个特定的载体（平台）线程，还是其他什么意思？

Answer 1

是的，这个后缀是当前载体线程的名称。

当我使用以下代码时

public static void main(String[] args) throws InterruptedException {
    Set<String> threadStrings = ConcurrentHashMap.newKeySet();
    try(var executor = Executors.newVirtualThreadPerTaskExecutor()) {
        executor.invokeAll(Collections.nCopies(16,
            () -> threadStrings.add(Thread.currentThread().toString())));
    }
    System.out.println("\tSimple Run");
    threadStrings.stream().sorted().forEachOrdered(System.out::println);

    threadStrings.clear();

    try(var executor = Executors.newVirtualThreadPerTaskExecutor()) {
        executor.invokeAll(Collections.nCopies(16, () -> {
            threadStrings.add(Thread.currentThread().toString());
            Thread.sleep(100);
            return threadStrings.add(Thread.currentThread().toString());
        }));
    }
    System.out.println("\tWith wait");
    threadStrings.stream().sorted().forEachOrdered(System.out::println);
}

它打印

        Simple Run
VirtualThread[#15]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#17]/runnable@ForkJoinPool-1-worker-2
VirtualThread[#18]/runnable@ForkJoinPool-1-worker-3
VirtualThread[#19]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#20]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#21]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#22]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#23]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#24]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#25]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#26]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#27]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#28]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#29]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#30]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#31]/runnable@ForkJoinPool-1-worker-4
        With wait
VirtualThread[#36]/runnable@ForkJoinPool-1-worker-2
VirtualThread[#37]/runnable@ForkJoinPool-1-worker-3
VirtualThread[#37]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#38]/runnable@ForkJoinPool-1-worker-4
VirtualThread[#38]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#39]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#39]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#40]/runnable@ForkJoinPool-1-worker-5
VirtualThread[#40]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#41]/runnable@ForkJoinPool-1-worker-6
VirtualThread[#41]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#42]/runnable@ForkJoinPool-1-worker-7
VirtualThread[#42]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#43]/runnable@ForkJoinPool-1-worker-5
VirtualThread[#43]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#44]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#44]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#45]/runnable@ForkJoinPool-1-worker-5
VirtualThread[#45]/runnable@ForkJoinPool-1-worker-6
VirtualThread[#46]/runnable@ForkJoinPool-1-worker-5
VirtualThread[#46]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#47]/runnable@ForkJoinPool-1-worker-2
VirtualThread[#49]/runnable@ForkJoinPool-1-worker-1
VirtualThread[#49]/runnable@ForkJoinPool-1-worker-8
VirtualThread[#50]/runnable@ForkJoinPool-1-worker-2
VirtualThread[#50]/runnable@ForkJoinPool-1-worker-6
VirtualThread[#51]/runnable@ForkJoinPool-1-worker-3
VirtualThread[#51]/runnable@ForkJoinPool-1-worker-5
VirtualThread[#52]/runnable@ForkJoinPool-1-worker-2
VirtualThread[#52]/runnable@ForkJoinPool-1-worker-8

^{（结果可能会有所不同）}

演示在执行sleep时载体线程可能如何变化。 但是在当前的快照（“build 18-loom+6-282”）中，不能再指定你自己的Executor并且没有方法可以查询关于它使用的载体线程的虚拟线程（除了通过toString()的隐式提示） toString() )。 所以，底层宿主线程的管理在这个版本中多半是黑盒子。

请记住，这是一个持续的发展。 目前尚不清楚这是否以及如何改变。