如何在一定次数的执行后停止计划重复执行的Runnable

Question

情况

我有一个Runnable。 我有一个类，使用ScheduledExecutorService和scheduleWithFixedDelay来调度此Runnable以执行。

目标

我想改变这个班安排了Runnable固定延迟执行无限期 ， 或直至它已经运行一定的次数，取决于被传递给构造函数的参数一些。

如果可能的话，我想使用相同的Runnable，因为它在概念上应该是“运行”相同的东西。

可能的方法

方法＃1

有两个Runnables，一个在多次执行后（它保持计数）取消计划，另一个不执行：

public class MyClass{
    private ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();

    public enum Mode{
        INDEFINITE, FIXED_NO_OF_TIMES
    }

    public MyClass(Mode mode){
        if(mode == Mode.INDEFINITE){
            scheduler.scheduleWithFixedDelay(new DoSomethingTask(), 0, 100, TimeUnit.MILLISECONDS);
        }else if(mode == Mode.FIXED_NO_OF_TIMES){
            scheduler.scheduleWithFixedDelay(new DoSomethingNTimesTask(), 0, 100, TimeUnit.MILLISECONDS);
        }
    }

    private class DoSomethingTask implements Runnable{
        @Override
        public void run(){
            doSomething();
        }
    }

    private class DoSomethingNTimesTask implements Runnable{
        private int count = 0;

        @Override
        public void run(){
            doSomething();
            count++;
            if(count > 42){
                // Cancel the scheduling.
                // Can you do this inside the run method, presumably using
                // the Future returned by the schedule method? Is it a good idea?
            }
        }
    }

    private void doSomething(){
        // do something
    }
}

我宁愿只有一个Runnable来执行doSomething方法。 将调度绑定到Runnable感觉不对。 你怎么看待这件事？

方法＃2

有一个Runnable用于执行我们想要定期运行的代码。 有一个单独的调度runnable，用于检查第一个Runnable运行的次数，并在达到一定量时取消。 这可能不准确，因为它是异步的。 感觉有点麻烦。 你怎么看待这件事？

方法＃3

扩展ScheduledExecutorService并添加方法“scheduleWithFixedDelayNTimes”。 也许这样的课程已经存在？ 目前，我正在使用Executors.newSingleThreadScheduledExecutor(); 获取我的ScheduledExecutorService实例。 我可能必须实现类似的功能来实例化扩展的ScheduledExecutorService。 这可能很棘手。 你怎么看待这件事？

没有调度程序方法[编辑]

我无法使用调度程序。 我可以改为：

for(int i = 0; i < numTimesToRun; i++){
    doSomething();
    Thread.sleep(delay);
}

并在某个线程中运行它。 你对那个怎么想的？ 您可能仍然可以使用runnable并直接调用run方法。

---

欢迎任何建议。 我正在寻找辩论，找到实现目标的“最佳实践”方式。

Answer 1

您可以在Future上使用cancel（）方法。 来自scheduleAtFixedRate的javadoc

Otherwise, the task will only terminate via cancellation or termination of the executor

下面是一些示例代码，它将Runnable包装在另一个中，跟踪原始运行的次数，并在运行N次后取消。

public void runNTimes(Runnable task, int maxRunCount, long period, TimeUnit unit, ScheduledExecutorService executor) {
    new FixedExecutionRunnable(task, maxRunCount).runNTimes(executor, period, unit);
}

class FixedExecutionRunnable implements Runnable {
    private final AtomicInteger runCount = new AtomicInteger();
    private final Runnable delegate;
    private volatile ScheduledFuture<?> self;
    private final int maxRunCount;

    public FixedExecutionRunnable(Runnable delegate, int maxRunCount) {
        this.delegate = delegate;
        this.maxRunCount = maxRunCount;
    }

    @Override
    public void run() {
        delegate.run();
        if(runCount.incrementAndGet() == maxRunCount) {
            boolean interrupted = false;
            try {
                while(self == null) {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        interrupted = true;
                    }
                }
                self.cancel(false);
            } finally {
                if(interrupted) {
                    Thread.currentThread().interrupt();
                }
            }
        }
    }

    public void runNTimes(ScheduledExecutorService executor, long period, TimeUnit unit) {
        self = executor.scheduleAtFixedRate(this, 0, period, unit);
    }
}

Answer 2

引用API描述（ ScheduledExecutorService.scheduleWithFixedDelay ）：

创建并执行一个周期性动作，该动作在给定的初始延迟之后首先被启用，并且随后在一次执行的终止和下一次执行的开始之间给定延迟。 如果任务的任何执行遇到异常，则后续执行被禁止。 否则，任务将仅通过取消或终止执行者来终止。

所以，最简单的事情是“只是抛出异常” （即使这被认为是不好的做法）：

static class MyTask implements Runnable {

    private int runs = 0;

    @Override
    public void run() {
        System.out.println(runs);
        if (++runs >= 20)
            throw new RuntimeException();
    }
}

public static void main(String[] args) {
    ScheduledExecutorService s = Executors.newSingleThreadScheduledExecutor();
    s.scheduleWithFixedDelay(new MyTask(), 0, 100, TimeUnit.MILLISECONDS);
}

Answer 3

到目前为止， sbridges解决方案似乎是最干净的解决方案，除了你提到的，它还有责任处理Runnable本身的执行次数。 它不应该与此有关，而是重复应该是处理调度的类的参数。 为实现这一点，我建议使用以下设计，为Runnables引入一个新的执行器类。 该类提供了两种用于调度任务的公共方法，它们是标准的Runnables ，具有有限或无限重复。 如果需要，可以传递相同的Runnable用于有限和无限调度（这对于扩展Runnable类以提供有限重复的所有提议的解决方案是不可能的）。 取消有限重复的处理完全封装在调度程序类中：

class MaxNScheduler
{

  public enum ScheduleType 
  {
     FixedRate, FixedDelay
  }

  private ScheduledExecutorService executorService =
     Executors.newSingleThreadScheduledExecutor();

  public ScheduledFuture<?> scheduleInfinitely(Runnable task, ScheduleType type, 
    long initialDelay, long period, TimeUnit unit)
  {
    return scheduleNTimes(task, -1, type, initialDelay, period, unit);
  }

  /** schedule with count repetitions */
  public ScheduledFuture<?> scheduleNTimes(Runnable task, int repetitions, 
    ScheduleType type, long initialDelay, long period, TimeUnit unit) 
  {
    RunnableWrapper wrapper = new RunnableWrapper(task, repetitions);
    ScheduledFuture<?> future;
    if(type == ScheduleType.FixedDelay)
      future = executorService.scheduleWithFixedDelay(wrapper, 
         initialDelay, period, TimeUnit.MILLISECONDS);
    else
      future = executorService.scheduleAtFixedRate(wrapper, 
         initialDelay, period, TimeUnit.MILLISECONDS);
    synchronized(wrapper)
    {
       wrapper.self = future;
       wrapper.notify(); // notify wrapper that it nows about it's future (pun intended)
    }
    return future;
  }

  private static class RunnableWrapper implements Runnable 
  {
    private final Runnable realRunnable;
    private int repetitions = -1;
    ScheduledFuture<?> self = null;

    RunnableWrapper(Runnable realRunnable, int repetitions) 
    {
      this.realRunnable = realRunnable;
      this.repetitions = repetitions;
    }

    private boolean isInfinite() { return repetitions < 0; }
    private boolean isFinished() { return repetitions == 0; }

    @Override
    public void run()
    {
      if(!isFinished()) // guard for calls to run when it should be cancelled already
      {
        realRunnable.run();

        if(!isInfinite())
        {
          repetitions--;
          if(isFinished())
          {
            synchronized(this) // need to wait until self is actually set
            {
              if(self == null)
              {
                 try { wait(); } catch(Exception e) { /* should not happen... */ }
              }
              self.cancel(false); // cancel gracefully (not throwing InterruptedException)
            }
          }
        }
      }
    }
  }

}

为了公平起见，管理重复的逻辑仍然是一个 Runnable ，但it'a一个Runnable完全内部的MaxNScheduler ，而Runnable通过调度任务必须不与调度的本质关注自身。 如果需要，通过每次执行RunnableWrapper.run时提供一些回调，这个问题也可以很容易地移出到调度程序中。 这会使代码稍微复杂化，并且需要保留一些RunnableWrapper的映射以及相应的重复，这就是我选择将计数器保留在RunnableWrapper类中的原因。

设置self时，我还在包装器上添加了一些同步。 理论上需要这样做，当执行结束时，可能还没有分配自我（一个相当理论的场景，但只能重复一次）。

正确处理取消，不会抛出InterruptedException ，如果在执行取消之前调度另一轮， RunnableWrapper将不会调用底层的Runnable 。

Answer 4

对于像轮询到某个超时之类的用例，我们可以使用Future.get()来使用更简单的解决方案。

/* Define task */
public class Poll implements Runnable {
    @Override
    public void run() {
        // Polling logic
    }
}

/* Create executor service */
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(5);

/* Schedule task - poll every 500ms */
ScheduledFuture<?> future = executorService.scheduleAtFixedRate(new Poll(), 0, 500, TimeUnit.MILLISECONDS);

/* Wait till 60 sec timeout */
try {
    future.get(60, TimeUnit.SECONDS);
} catch (TimeoutException e) {
    scheduledFuture.cancel(false);
    // Take action on timeout
}

Answer 5

你的第一种方法似乎没问题 您可以通过将mode对象传递给它的构造函数来组合两种类型的runnable（或者将-1作为必须运行的最大次数传递-1），并使用此模式来确定是否必须取消runnable：

private class DoSomethingNTimesTask implements Runnable{
    private int count = 0;
    private final int limit;

    /**
     * Constructor for no limit
     */
    private DoSomethingNTimesTask() {
        this(-1);
    }

    /**
     * Constructor allowing to set a limit
     * @param limit the limit (negative number for no limit)
     */
    private DoSomethingNTimesTask(int limit) {
        this.limit = limit;
    }

    @Override
    public void run(){
        doSomething();
        count++;
        if(limit >= 0 && count > limit){
            // Cancel the scheduling
        }
    }
}

您必须将预定的未来传递给您的任务才能使其自行取消，否则您可能会抛出异常。

Answer 6

这是我的建议（我认为它处理了问题中提到的所有案例）：

public class RepeatedScheduled implements Runnable {

    private int repeatCounter = -1;
    private boolean infinite;

    private ScheduledExecutorService ses;
    private long initialDelay;
    private long delay;
    private TimeUnit unit;

    private final Runnable command;
    private Future<?> control;

    public RepeatedScheduled(ScheduledExecutorService ses, Runnable command,
        long initialDelay, long delay, TimeUnit unit) {

        this.ses = ses;
        this.initialDelay = initialDelay;
        this.delay = delay;
        this.unit = unit;

        this.command = command;
        this.infinite = true;

    }

    public RepeatedScheduled(ScheduledExecutorService ses, Runnable command,
        long initialDelay, long delay, TimeUnit unit, int maxExecutions) {

        this(ses, command, initialDelay, delay, unit);
        this.repeatCounter = maxExecutions;
        this.infinite = false;

    }

    public Future<?> submit() {

        // We submit this, not the received command
        this.control = this.ses.scheduleWithFixedDelay(this,
            this.initialDelay, this.delay, this.unit);

        return this.control;

    }

    @Override
    public synchronized void run() {

        if ( !this.infinite ) {
            if ( this.repeatCounter > 0 ) {
                this.command.run();
                this.repeatCounter--;
            } else {
                this.control.cancel(false);
            }
        } else {
            this.command.run();
        }

    }

}

此外，它允许外部方停止来自submit()方法返回的Future所有内容。

用法：

Runnable MyRunnable = ...;
// Repeat 20 times
RepeatedScheduled rs = new RepeatedScheduled(
    MySes, MyRunnable, 33, 44, TimeUnit.SECONDS, 20);
Future<?> MyControl = rs.submit();
...

Answer 7

我一直在寻找完全相同的功能，并选择了org.springframework.scheduling.Trigger 。

下面是完整测试工作示例（如果代码中存在太多洪水，则抱歉）applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns:task="http://www.springframework.org/schema/task"
 xmlns:util="http://www.springframework.org/schema/util"
 xmlns:context="http://www.springframework.org/schema/context"
 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context/ http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/util/ http://www.springframework.org/schema/util/spring-util.xsd
        http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.0.xsd">

    <bean id="blockingTasksScheduler" class="org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler">
        <property name="poolSize" value="10" />
    </bean>

    <task:scheduler id="deftaskScheduler" pool-size="10" />

</beans>

JAVA

package com.alz.springTests.schedulerTest;

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;
import java.util.Date;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.TriggerContext;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;

public class ScheduledTest {

    private static ApplicationContext applicationContext;
    private static TaskScheduler taskScheduler;

    private static final class SelfCancelableTask implements Runnable, Trigger {
        Date creationTime = new Date();
        AtomicInteger counter = new AtomicInteger(0);
        private volatile boolean shouldStop = false;
        private int repeatInterval = 3; //seconds

        @Override
        public void run() {
            log("task: run started");

            // simulate "doing job" started
            int sleepTimeMs = ThreadLocalRandom.current().nextInt(500, 2000+1);
            log("will sleep " + sleepTimeMs + " ms");
            try {
                Thread.sleep(sleepTimeMs);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // "doing job" finished

            int i = counter.incrementAndGet();
            if (i > 5) { //cancel myself
                logErr("Attempts exceeded, will mark as shouldStop");
                shouldStop = true;

            } else {
                log("task: executing cycle #"+i);
            }
        }

        @Override
        public Date nextExecutionTime(TriggerContext triggerContext) {
            log("nextExecutionTime: triggerContext.lastActualExecutionTime() " + triggerContext.lastActualExecutionTime());
            log("nextExecutionTime: triggerContext.lastCompletionTime() " + triggerContext.lastCompletionTime());
            log("nextExecutionTime: triggerContext.lastScheduledExecutionTime() " + triggerContext.lastScheduledExecutionTime());

            if (shouldStop) 
                return null;

            if (triggerContext.lastCompletionTime() == null) {
                LocalDateTime ldt = creationTime.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime().plus(repeatInterval, ChronoUnit.SECONDS);
                return Date.from(ldt.atZone(ZoneId.systemDefault()).toInstant());
            } else {
                LocalDateTime ldt = triggerContext.lastCompletionTime().toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime().plus(repeatInterval, ChronoUnit.SECONDS);
                return Date.from(ldt.atZone(ZoneId.systemDefault()).toInstant());               
            }

        }

    }

    private static void log(String log) {
        System.out.printf("%s [%s] %s\r\n", LocalDateTime.now(), Thread.currentThread(), log);
    }

    private static void logErr(String log) {
        System.err.printf("%s [%s] %s\r\n", LocalDateTime.now(), Thread.currentThread(), log);
    }

    public static void main(String[] args) {

        log("main: Stated...");

        applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");

        taskScheduler = (TaskScheduler) applicationContext.getBean("blockingTasksScheduler");

        ScheduledThreadPoolExecutor scheduledThreadPoolExecutor = ((ThreadPoolTaskScheduler)taskScheduler).getScheduledThreadPoolExecutor();

        SelfCancelableTask selfCancelableTask = new SelfCancelableTask();
        taskScheduler.schedule(selfCancelableTask, selfCancelableTask);


        int waitAttempts = 0;
        while (waitAttempts < 30) {
            log("scheduledPool pending tasks: " + scheduledThreadPoolExecutor.getQueue().size());

            try {
                Thread.sleep(1*1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            waitAttempts++;

        }

        log("main: Done!");


    }

}