“主”线程的Java执行器

Question

我想从程序的“主”线程创建一个Executor (类似于Android中的主活套 )，然后运行直到它处理了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);
  }
}

但我得到了一个IllegalThreadState异常：

SEVERE: RuntimeException while executing runnable MyApp$$Lambda$20/0x00000008000a6440@71f06a3c with executor java.util.concurrent.Executors$FinalizableDelegatedExecutorService@47add263
java.lang.IllegalThreadStateException
    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$DelegatedExecutorService.execute(Executors.java:687)
    at com.google.common.util.concurrent.AbstractFuture.executeListener(AbstractFuture.java:1137)
    at com.google.common.util.concurrent.AbstractFuture.complete(AbstractFuture.java:957)
    at com.google.common.util.concurrent.AbstractFuture.set(AbstractFuture.java:726)
    at com.google.common.util.concurrent.TrustedListenableFutureTask$TrustedFutureInterruptibleTask.afterRanInterruptibly(TrustedListenableFutureTask.java:131)
    at com.google.common.util.concurrent.InterruptibleTask.run(InterruptibleTask.java:133)
    at com.google.common.util.concurrent.TrustedListenableFutureTask.run(TrustedListenableFutureTask.java:78)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)

我可以在一个新线程上启动一个ExecutorService，然后等待它，但这似乎是浪费。

是否有一种从当前线程创建Executor 的好方法，并等待它处理提交给它的所有东西？

Answer 1

使用番石榴的MoreExecutors.newDirectExecutorService()

这将确保提交的代码将在ThreadPool的同一个线程中执行。我知道，它不是主线程，但至少您不像您想要的那样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

invokeAll()文档化的这里方法等待所有任务的完成

你能做到的

executorService.invokeAll();

请跟随这个职位获得更多解释

Answer 3

您正在尝试在主线程中执行回调。简单的方法是调用get()

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

如果您想异步执行回调，您可能对CompletionStage感兴趣。

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