[英]Is it possible to schedule a CompletableFuture?
Is there any way to schedule CompletableFuture in Java?有没有办法在 Java 中安排 CompletableFuture? What I wanted to do is to schedule a task to be executed with some delay, and chain it with other operations to be performed asynchronously when it completes.我想要做的是安排一个任务以一些延迟执行,并在它完成时将它与其他异步执行的操作链接起来。 So far I didn't find any way to do this.到目前为止,我还没有找到任何方法来做到这一点。
For good ol' Futures we have eg ScheduledExecutorService, where we can schedule a task to be executed with some delay like this:对于好的 ol' Futures,我们有例如 ScheduledExecutorService,我们可以在其中安排一个任务以延迟执行,如下所示:
ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
Future<String> future = scheduledExecutorService.schedule(() -> "someValue", 10, TimeUnit.SECONDS);
Is there any similar way for CompletableFutures? CompletableFutures 有没有类似的方法?
As said , there is support in Java 9.如前所述,Java 9 中有支持。
But it's not hard to create a similar feature under Java 8;但是在 Java 8 下创建类似的特性并不难; you already named the necessary elements: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);
}
which can be used similarly to the Java 9 feature:可以与 Java 9 功能类似地使用:
Executor afterTenSecs = delayedExecutor(10L, TimeUnit.SECONDS);
CompletableFuture<String> future
= CompletableFuture.supplyAsync(() -> "someValue", afterTenSecs);
future.thenAccept(System.out::println).join();
Care must be taken to avoid that the shared scheduled executor's threads prevent the JVM from terminating.必须注意避免共享调度执行程序的线程阻止 JVM 终止。 The alternative to a zero core pool size is to use daemon threads: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;
});
If you're using Java 9+ then CompletableFuture#delayedExecutor(long,TimeUnit)
may fit your needs: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).返回一个新的 Executor,它在给定的延迟后(如果非正则没有延迟)将任务提交给默认的 executor。 Each delay commences upon invocation of the returned executor's
execute
method.每次延迟都在调用返回的执行程序的execute
方法时开始。
Executor delayed = CompletableFuture.delayedExecutor(10L, TimeUnit.SECONDS);
CompletableFuture.supplyAsync(() -> "someValue", delayed)
.thenAccept(System.out::println)
.join();
There's also an overload where you can specify the Executor
to use in place of the "default executor".还有一个重载,您可以在其中指定要使用的Executor
来代替“默认执行器”。
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