Java 虚拟线程调度器 ForkJoinPool 自定义参数设置

主要参数

• parallelism
• maxPoolSize
• minRunnable

参数设置

方式一

程序启动时设置。

System.setProperty("jdk.virtualThreadScheduler.parallelism", "16");
System.setProperty("jdk.virtualThreadScheduler.maxPoolSize", "256");

方式二

命令行中指定。

java -jar -Djdk.virtualThreadScheduler.parallelism=16 -Djdk.virtualThreadScheduler.maxPoolSize=256 app.jar

说明

Java21~`Java25中，还无法为VirtualThread自定义ForkJoinPool`。

源码

final class VirtualThread extends BaseVirtualThread {

    private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();

    private final Executor scheduler;
    
    @SuppressWarnings("removal")
    private static ForkJoinPool createDefaultScheduler() {
        ForkJoinWorkerThreadFactory factory = pool -> {
            PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
            return AccessController.doPrivileged(pa);
        };
        PrivilegedAction<ForkJoinPool> pa = () -> {
            int parallelism, maxPoolSize, minRunnable;
            String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
            String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
            String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
            ...
        }
    }
    
    /**
     * Creates a new {@code VirtualThread} to run the given task with the given
     * scheduler. If the given scheduler is {@code null} and the current thread
     * is a platform thread then the newly created virtual thread will use the
     * default scheduler. If given scheduler is {@code null} and the current
     * thread is a virtual thread then the current thread's scheduler is used.
     *
     * @param scheduler the scheduler or null
     * @param name thread name
     * @param characteristics characteristics
     * @param task the task to execute
     */
    VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
        super(name, characteristics, /*bound*/ false);
        Objects.requireNonNull(task);

        // choose scheduler if not specified
        if (scheduler == null) {
            Thread parent = Thread.currentThread();
            if (parent instanceof VirtualThread vparent) {
                scheduler = vparent.scheduler;
            } else {
                scheduler = DEFAULT_SCHEDULER;
            }
        }

        this.scheduler = scheduler;
        this.cont = new VThreadContinuation(this, task);
        this.runContinuation = this::runContinuation;
    }
    
}