Class AsyncSupport

src/main/java/org/apache/groovy/runtime/async/AsyncSupport.java:83–696

Internal runtime support for the async/await/defer language features. This class contains the actual implementation invoked by compiler-generated code. User code should prefer the static methods on groovy.concurrent.Awaitable for combinators and configuration.

 * @since 6.0.0
 */
public class AsyncSupport {

    private static final boolean VIRTUAL_THREADS_AVAILABLE;
    private static final Executor VIRTUAL_THREAD_EXECUTOR;
    private static final int FALLBACK_MAX_THREADS;
    private static final Executor FALLBACK_EXECUTOR;

    static {
        Executor vtExecutor = null;
        boolean vtAvailable = false;
        try {
            MethodHandle mh = MethodHandles.lookup().findStatic(
                    Executors.class, "newVirtualThreadPerTaskExecutor",
                    MethodType.methodType(ExecutorService.class));
            vtExecutor = (Executor) mh.invoke();
            vtAvailable = true;
        } catch (Throwable ignored) {
            // JDK < 21 — virtual threads not available
        }
        VIRTUAL_THREAD_EXECUTOR = vtExecutor;
        VIRTUAL_THREADS_AVAILABLE = vtAvailable;

        FALLBACK_MAX_THREADS = getIntegerSafe("groovy.async.parallelism", 256);
        if (!VIRTUAL_THREADS_AVAILABLE) {
            FALLBACK_EXECUTOR = new ThreadPoolExecutor(
                    0, FALLBACK_MAX_THREADS,
                    60L, TimeUnit.SECONDS,
                    new SynchronousQueue<>(),
                    r -> {
                        Thread t = new Thread(r);
                        t.setDaemon(true);
                        @SuppressWarnings("deprecation")
                        long id = t.getId();
                        t.setName("groovy-async-" + id);
                        return t;
                    },
                    new ThreadPoolExecutor.CallerRunsPolicy());
        } else {
            FALLBACK_EXECUTOR = null;
        }
    }

    private static volatile Executor defaultExecutor = createDefaultExecutor();

    private static final ScheduledExecutorService SCHEDULER =
            Executors.newSingleThreadScheduledExecutor(r -> {
                Thread t = new Thread(r, "groovy-async-scheduler");
                t.setDaemon(true);
                return t;
            });

    private AsyncSupport() { }

    // ---- executor configuration -----------------------------------------

    /** Returns the shared scheduler for delays, timeouts, and scope deadlines. */
    public static ScheduledExecutorService getScheduler() {
        return SCHEDULER;