我有一个Runnable。我有一个类，使用带有scheduleWithFixedDelay的ScheduledExecutorService来安排此Runnable执行。
我想改变这个类来安排Runnable进行固定延迟执行 无限期或，直到它运行了一定次数，具体取决于某些参数传递给构造函数。
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”的东西。
有两个Runnables，一个在多次执行后（它保留计数）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。你怎么看待这个？
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。你怎么看待这个？
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();来获取我的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。你怎么看待这个？
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);
}
在某个帖子中运行它。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。
答案 0 :(得分：61)
您可以在Future上使用cancel（）方法。来自scheduleAtFixedRate
的javadocOtherwise, 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);
}
}
答案 1 :(得分：8)
引用API说明（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，则后续执行将被禁止。否则，任务将仅通过取消或终止执行程序来终止。
所以，最容易的事情是“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);
}
答案 2 :(得分：5)
到目前为止， sbridges 解决方案似乎是最干净的解决方案，除了您提到的内容之外，它还要负责处理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。为实现这一目标，我建议采用以下设计，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，这些方法是标准Runnables，具有有限或无限重复。如果需要，可以为有限和无限调度传递相同的Runnable（对于扩展Runnable类以提供有限重复的所有提议的解决方案，这是不可能的）。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)
}
}
}
}
}
}
}
公平地说，管理重复的逻辑仍然是 a Runnable，但它是Runnable完全内部的MaxNScheduler，而为调度而传递的Runnable任务不必关心调度的性质。此外，如果需要，可以通过每次执行RunnableWrapper.run时提供一些回调，将此问题轻松移出到调度程序中。这会使代码稍微复杂化并且需要保留一些RunnableWrapper s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。
我在设置self时也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（一个非常理论的场景，但只能重复一次）。
取消处理得很优雅，不会抛出InterruptedException，如果在执行取消之前的情况下，会安排另一轮，RunnableWrapper将不会调用基础Runnable。
答案 3 :(得分：1)
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这两种类型的runnable（或者传递-1作为它必须运行的最大次数），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。
答案 4 :(得分：1)
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Future方法返回的submit()内的所有内容。
用法：
Runnable MyRunnable = ...;
// Repeat 20 times
RepeatedScheduled rs = new RepeatedScheduled(
MySes, MyRunnable, 33, 44, TimeUnit.SECONDS, 20);
Future<?> MyControl = rs.submit();
...
答案 5 :(得分：1)
对于诸如轮询直到特定超时之类的用例，我们可以使用Future.get()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
}
答案 6 :(得分：0)
我一直在寻找完全相同的功能，因此选择了org.springframework.scheduling.Trigger。
下面是经过全面测试的工作示例（很抱歉，如果代码中的洪水过多） 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!");
}
}