同步方法阻塞执行

Question

我正在实施一个包含三个 class 的虚拟程序，以便更直观地了解 Future 的工作原理。我的问题是，有时程序会锁定在同步方法上，无法继续。我找不到原因。有人能找出 none 的战士打印“我赢了”行的原因吗？

阻塞时我的当前输出：

Fighter1

Fighter1 has entered the sync method

Fighter2

Fighter2 has entered the sync method

代码如下

主要class:

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class TmpTest {
private static final ExecutorService executorService = 
  Executors.newFixedThreadPool(2);

  public static void main(final String... args) {

    final Fighter fighter1 = new Fighter("Fighter1");
    final Fighter fighter2 = new Fighter("Fighter2");

    final Future<String> submitFighter1 = executorService.submit(fighter1);
    final Future<String> submitFighter2 = executorService.submit(fighter2);

    while (!submitFighter1.isDone() || !submitFighter2.isDone()) {
        if (submitFighter1.isDone()) {
            System.out.println("Fighter 1 wins!");
            submitFighter2.cancel(true);
            executorService.shutdown();
        } else if (submitFighter2.isDone()) {
            submitFighter1.cancel(true);
            System.out.println("Fighter 2 wins!");
            executorService.shutdown();
        }
    }
  }
}

斗士class:

class Fighter implements Callable<String> {

  private final String fighterName;
  private final ClassWithSyncMethod classWithSyncMethod;

  public Fighter(final String fighterName) {
    this.fighterName = fighterName;
    classWithSyncMethod = new ClassWithSyncMethod(fighterName);
  }

  @Override
  public String call() throws Exception {
    return classWithSyncMethod.syncMethod();
  }
}

具有同步方法的虚拟 class：

class ClassWithSyncMethod {

  private final String fighterName;

  public ClassWithSyncMethod(final String fighterName) {
    this.fighterName = fighterName;
  }

  public synchronized String syncMethod() {
    System.out.println(fighterName + " has entered the sync method");
    try {
        Thread.sleep(1000);
    } catch (final InterruptedException e) {
        System.out.println("Exception trying to sleep the fighter " + fighterName + ";" + e);
    }
    return fighterName + " shouts: I won!";
  }
}

Answer 1

这与同步无关。每个战斗机在不同的对象上同步，因此它们不会相互干扰。

您看不到 "I won" 行的原因要简单得多——您从不打印它。 ClassWithSyncMethod#syncMethod() 方法（由 Fighter#call() 返回）不打印任何内容，它只是 returns 一个值。如果你想打印它，你必须自己从 main 打印它。

例如：

while (!submitFighter1.isDone() || !submitFighter2.isDone()) {
    if (submitFighter1.isDone()) {
        System.out.println("Fighter 1 wins!");
        System.out.println(submitFighter1.get()); // Here!
        submitFighter2.cancel(true);
        executorService.shutdown();
    } else if (submitFighter2.isDone()) {
        submitFighter1.cancel(true);
        System.out.println("Fighter 2 wins!");
        System.out.println(submitFighter2.get()); // And here!
        executorService.shutdown();
    }
}

同步方法阻塞执行

Synchronized method blocks execution

java

future

executorservice

synchronized