“主”线程的 Java 执行器

Question

我想Executor从程序的&ldquo;主&rdquo;线程（类似于 Android 中的主循环程序）创建一个，然后运行直到它处理完提交给它的所有内容：public class MyApp {  private static Callable<Integer> task = () -> {    // ... return an int somehow ...  };  public static void main(String[] args) throws ExecutionException, InterruptedException {    ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1));    Thread main = Thread.currentThread();    ExecutorService executorService = Executors.newSingleThreadExecutor(r -> main);    service.submit(task).addListener(() -> {      /// ... do something with the result ...    }, executorService);    executorService.awaitTermination(100, TimeUnit.SECONDS);  }}但我得到一个IllegalThreadState例外：SEVERE: RuntimeException while executing runnable MyApp$$Lambda$20/0x00000008000a6440@71f06a3c with executor java.util.concurrent.Executors$[e-mail]ion    at java.base/java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:926)    at java.base/java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1343)    at java.base/java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:687)    at com.google.common.util.concurrent.AbstractFuture.executeListener(AbstractFuture.java:1137)    at com.google.common.util.concurrent.AbstractFuture.complete(AbstractFuture.java:957)    at com.google.common.util.concurrent.AbstractFuture.set(AbstractFuture.java:726)    我可以在一个新线程上开始一个ExecutorService线程，然后等待它，但这似乎很浪费。有没有一种从当前线程创建一个Executor并等待它处理已提交给它的所有内容的好方法？

Answer 1

使用 Guava 的MoreExecutors.newDirectExecutorService()

这将确保提交的代码将在 ThreadPool 的同一线程中执行。我知道，这不是主线程，但至少您不会像您想要的那样只为侦听器创建其他新线程。

import com.google.common.util.concurrent.*;

import org.junit.jupiter.api.Test;

import java.util.concurrent.*;

class ExecutorTest {

  private static Callable<Integer> task = () -> {

    System.out.println("in call: " + Thread.currentThread().getName());

    TimeUnit.SECONDS.sleep(1);

    return 0;

  };

  @Test

  void test() throws InterruptedException {

    ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1));

    ExecutorService executor = MoreExecutors.newDirectExecutorService();

    service.submit(task).addListener(() -> {

      System.out.println("in listener: " + Thread.currentThread().getName());

    }, executor);

    executor.awaitTermination(2, TimeUnit.SECONDS);

  }

}

Answer 2

您正在尝试在主线程中执行回调。直接的方法是调用get()：

YourResult result = service.submit(task).get();
/* Do something with your result... */

如果您想异步执行回调，您可能会对CompletionStage

CompletableFuture.runAsync(task).thenAccept(r -> /* do something with result */);

Answer 3

此处invokeAll()记录的方法 等待所有任务完成 您可以这样做

executorService.invokeAll();

Answer 4

您可能正在寻找类似的东西CompletionService：您向其提交任务，它会按完成顺序返回给您。

ExecutorService service = Executors.newFixedThreadPool(1);

ExecutorCompletionService<Integer> comp = new ExecutorCompletionService<>(service);

comp.submit(task);

// ... I assume you want to submit N tasks.

for (int i = 0; i < N; ++i) {

  Future<Integer> future = comp.take();

  Integer result = future.get();

  // ... do something with the result ...

}

这将在项目完成后立即对其进行处理。如果你能等到你拥有一切，然后一次性处理它，你可以使用番石榴Futures.allAsList：

ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(1));

List<Callable<Integer>> tasks = ...;

List<ListenableFuture<Integer>> futures = new ArrayList<>();

for (Callable<Integer> task : tasks) {

  futures.add(service.submit(task));

}

ListenableFuture<List<Integer>> resultsFuture = Futures.allAsList(futures);

List<Integer> results = resultsFuture.get();

// Process the results.