完全的未来。allOf（）在个人期货交易后未完成

Question

当我使用完全的未来。allOf（）组合javadoc中描述的独立可完成的未来，在提供给该方法的所有未来之后，它不能可靠地完成。例如。：

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class CompletableFutureTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Runnable dummyTask = () -> {
            try {
                Thread.sleep(200);
            } catch (InterruptedException ignored) {
            }
        };

        CompletableFuture<Void> f1 = CompletableFuture.runAsync(dummyTask);
        CompletableFuture<Void> f2 = CompletableFuture.runAsync(dummyTask);
        CompletableFuture[] all = {f1, f2};
        f1.whenComplete((aVoid, throwable) -> System.out.println("Completed f1"));
        f2.whenComplete((aVoid, throwable) -> System.out.println("Completed f2"));
        CompletableFuture<Void> allOf = CompletableFuture.allOf(all);
        allOf.whenComplete((aVoid, throwable) -> {
                    System.out.println("Completed allOf");
                }
        );
        allOf.join();
        System.out.println("Joined");
    }
}

结果如下：

Completed f2
Joined
Completed allOf
Completed f1

我希望日志“Joined”和“Completed allOf”写在“Completed f1”和“Completed f2”之后。为了让事情变得更加混乱，阵列中的未来顺序似乎是头等大事。如果我换了台词

CompletableFuture[] all = {f1, f2};

到

CompletableFuture[] all = {f2, f1};

结果输出更改为：

Completed allOf
Completed f1
Completed f2
Joined

更糟糕的是，如果我多次运行完全相同的代码，顺序会再次改变。我可以理解“f1”和“f2”的顺序是随机变化的，“allOf”和“Joed”也是如此。但这真的很令人惊讶。

以防万一：这是Windows 7上的JDK 1.8.091。

Answer 1

调用wenComplete方法上的join

allOf.whenComplete((aVoid, throwable) -> {
                System.out.println("Completed allOf");
            }
    ).join();

Answer 2

这没关系-没有人保证回调的顺序。

Answer 3

f1。whenComplete返回独立于f1的新未来AllOf将等待f1完成，但不等待在完成时传递给的lambda完成。为了得到你想要的结果，你可以尝试以下方法：

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class CompletableFutureTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Runnable dummyTask = () -> {
            try {
                Thread.sleep(200);
            } catch (InterruptedException ignored) {
            }
        };

        CompletableFuture<Void> f1 = CompletableFuture.runAsync(dummyTask);
        CompletableFuture<Void> f2 = CompletableFuture.runAsync(dummyTask);
        f1 = f1.whenComplete((aVoid, throwable) -> System.out.println("Completed f1"));
        f2 = f2.whenComplete((aVoid, throwable) -> System.out.println("Completed f2"));
        CompletableFuture[] all = {f1, f2};
        CompletableFuture<Void> allOf = CompletableFuture.allOf(all);
        allOf.whenComplete((aVoid, throwable) -> {
            System.out.println("Completed allOf");
        });
        allOf.join();
        System.out.println("Joined");
    }
}