是否可以安排 CompletableFuture？

Question

有什么方法可以在 Java 中安排 CompletableFuture 吗？我想做的是安排一个任务以一定的延迟执行，并在它完成时将其与其他异步执行的操作链接起来。到目前为止我还没有找到任何方法来做到这一点。

为了更好的期货，我们有例如ScheduledExecutorService，我们可以在其中安排一个任务以像这样的延迟执行：

ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
Future<String> future = scheduledExecutorService.schedule(() -> "someValue", 10, TimeUnit.SECONDS);

CompletableFutures有没有类似的方法？

Answer 1

如果您使用的是 Java 9+，那么 CompletableFuture#delayedExecutor(long,TimeUnit) 可能满足您的需求：

Returns a new Executor that submits a task to the default executor after the given delay (or no delay if non-positive). Each delay commences upon invocation of the returned executor's execute method.

Executor delayed = CompletableFuture.delayedExecutor(10L, TimeUnit.SECONDS);
CompletableFuture.supplyAsync(() -> "someValue", delayed)
    .thenAccept(System.out::println)
    .join();

还有 an overload，您可以在其中指定 Executor 来代替 "default executor"。

Answer 2

，在 Java 9.

中有支持

但在 Java8 下创建类似的功能并不难；您已经命名了必要的元素：

// prefer this constructor with zero core threads for a shared pool,
// to avoid blocking JVM exit
static final ScheduledExecutorService SCHEDULER = new ScheduledThreadPoolExecutor(0);
static Executor delayedExecutor(long delay, TimeUnit unit)
{
  return delayedExecutor(delay, unit, ForkJoinPool.commonPool());
}
static Executor delayedExecutor(long delay, TimeUnit unit, Executor executor)
{
  return r -> SCHEDULER.schedule(() -> executor.execute(r), delay, unit);
}

可以类似于 Java 9 功能使用：

Executor afterTenSecs = delayedExecutor(10L, TimeUnit.SECONDS);
CompletableFuture<String> future 
  = CompletableFuture.supplyAsync(() -> "someValue", afterTenSecs);

future.thenAccept(System.out::println).join();

必须注意避免共享调度执行程序的线程阻止 JVM 终止。零核心池大小的替代方法是使用守护线程：

static final ScheduledExecutorService SCHEDULER
  = Executors.newSingleThreadScheduledExecutor(r -> {
    Thread t = new Thread(r);
    t.setDaemon(true);
    return t;
  });

是否可以安排 CompletableFuture？

Is it possible to schedule a CompletableFuture?

java

concurrency

scheduled-tasks

completable-future