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java - “主”线程的 Java 执行器

问题描述

我想Executor从程序的“主”线程（类似于 Android 中的主循环器）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$20/0x00000008000a6440@71f06a3c with executor java.util.concurrent.Executors$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)

我可以开始ExecutorService一个新线程，然后等待，但这似乎很浪费。

有没有一种Executor从当前线程创建一个并等待它处理已提交给它的所有内容的好方法？

标签： javaguava

解决方案

使用番石榴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，它不是主线程，但至少您不会像您想要的那样仅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);
  }
}

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