执行器 System.out.println 未在控制台中显示

Question

package com.company;

import java.io.Console;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Main {

    static boolean isToastShewnLeft = false;

    public static void main(String[] args) {

        showToastLeft("first", "", "");
        showToastLeft("second", "", "");
        showToastLeft("third", "", "");
        showToastLeft("fourth", "", "");
        showToastLeft("fifth", "", "");
    }

    public static void showToastLeft(final String paramToastString1, final String paramToastString2, final String paramToastString3) {

        final long start = System.currentTimeMillis();

        ScheduledExecutorService worker1 = Executors.newSingleThreadScheduledExecutor();

        ScheduledExecutorService worker2 = Executors.newSingleThreadScheduledExecutor();

        if (isToastShewnLeft) {

            final Runnable r = new Runnable() {
                @SuppressWarnings("StatementWithEmptyBody")
                public void run() {
                    while (isToastShewnLeft) {

                    }

                    isToastShewnLeft = true;

                    //This line does not appear in console output
                    //I can set a breakpoint on this println and see that it does execute
                    System.out.println(paramToastString1);

                    ScheduledExecutorService worker3 = Executors.newSingleThreadScheduledExecutor();

                    final Runnable r2 = new Runnable() {
                        public void run() {
                            isToastShewnLeft = false;

                            System.out.println(System.currentTimeMillis() - start + " Set toast not shewn");
                        }
                    };

                    worker3.schedule(r2, 5, TimeUnit.SECONDS);

                }
            };

            worker1.schedule(r, 0, TimeUnit.SECONDS);

        } else {
            isToastShewnLeft = true;

            System.out.println(paramToastString1);

            final Runnable r2 = new Runnable() {
                public void run() {
                    isToastShewnLeft = false;
                    System.out.println(System.currentTimeMillis() - start + " Set toast not shewn");
                }
            };

            worker2.schedule(r2, 5, TimeUnit.SECONDS);

        }
    }
}
            /Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/bin/java -Didea.launcher.port=7543 "-Didea.launcher.bin.path=/Applications/IntelliJ IDEA 14 CE.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath "/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/javafx-doclet.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/lib/tools.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/htmlconverter.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_75.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Users/ericsepich/IdeaProjects/untitled1/out/production/untitled1:/Applications/IntelliJ IDEA 14 CE.app/Contents/lib/idea_rt.jar" com.intellij.rt.execution.application.AppMain com.company.Main
            first
            5008 Set toast not shewn

我的意图是在每次调用 showToastLeft 时间隔 5 秒显示文本。使用 println from 是否有可能有问题执行者线程？我正在使用 IntelliJ idea 作为我的 IDE.

我将发布一个屏幕截图，显示我的调试器中的布尔值为真。

感谢您的任何回复....

Answer 1

您有多个线程在没有任何并发保护的情况下读写 isToastShewnLeft 变量。尝试在 synchronized 中包含对 isToastShewnLeft 的所有 read/write 操作，看看这是否有所作为。这里的问题可能是与线程相关的可见性问题：线程保留自己的变量副本并重新排序操作以提高效率的微妙情况。同步是使用任何共享变量防止这种情况的一种方法。 Here is one good explanation of visibility, and here is another。

除了 synchronized，您还可以使用 java.util.concurrent.AtomicBoolean，如果您真的很关心性能（考虑到 5 秒的间隔，我对此表示怀疑）。仅将 isToastShewnLeft 变成 volatile 变量是否可以逃脱，这有点主观，但鉴于 isToastShewnLeft 的状态会影响写入的内容，我会回避它.

Answer 2

您没有让 Java 线程系统有机会在您的线程之间共享 CPU。

                while (isToastShewnLeft) {
                  // Add this.
                  Thread.sleep(10);
                }

执行器 System.out.println 未在控制台中显示

Executor System.out.println not showing in console

java

scheduledexecutorservice