Java 如何在ScheduledThreadPoolExecutor中停止一个我认为是';完成了
我有一个ScheduledThreadPoolExecutor,我用它来计划以固定速率运行的任务。我希望任务以指定的延迟运行最多10次,直到“成功”。在那之后,我不希望任务被重试。因此,基本上,当我希望停止调度任务时,我需要停止运行该任务,但不需要关闭ScheduledThreadPoolExecutor。知道我该怎么做吗 这里有一些伪代码-Java 如何在ScheduledThreadPoolExecutor中停止一个我认为是';完成了,java,scheduled-tasks,scheduling,scheduler,Java,Scheduled Tasks,Scheduling,Scheduler,我有一个ScheduledThreadPoolExecutor,我用它来计划以固定速率运行的任务。我希望任务以指定的延迟运行最多10次,直到“成功”。在那之后,我不希望任务被重试。因此,基本上,当我希望停止调度任务时,我需要停止运行该任务,但不需要关闭ScheduledThreadPoolExecutor。知道我该怎么做吗 这里有一些伪代码- public class ScheduledThreadPoolExecutorTest { public static ScheduledThrea
public class ScheduledThreadPoolExecutorTest
{
public static ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(15); // no multiple instances, just one to serve all requests
class MyTask implements Runnable
{
private int MAX_ATTEMPTS = 10;
public void run()
{
if(++attempt <= MAX_ATTEMPTS)
{
doX();
if(doXSucceeded)
{
//stop retrying the task anymore
}
}
else
{
//couldn't succeed in MAX attempts, don't bother retrying anymore!
}
}
}
public void main(String[] args)
{
executor.scheduleAtFixedRate(new ScheduledThreadPoolExecutorTest().new MyTask(), 0, 5, TimeUnit.SECONDS);
}
}
公共类ScheduledThreadPoolExecutorTest
{
public static ScheduledThreadPoolExecutor executor=new ScheduledThreadPoolExecutor(15);//没有多个实例,只有一个实例为所有请求提供服务
类MyTask实现Runnable
{
私人int最大尝试次数=10;
公开募捐
{
如果(++尝试运行此测试,它将打印1 2 3 4 5
并停止
public class ScheduledThreadPoolExecutorTest {
static ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(15); // no
static ScheduledFuture<?> t;
static class MyTask implements Runnable {
private int attempt = 1;
public void run() {
System.out.print(attempt + " ");
if (++attempt > 5) {
t.cancel(false);
}
}
}
public static void main(String[] args) {
t = executor.scheduleAtFixedRate(new MyTask(), 0, 1, TimeUnit.SECONDS);
}
}
公共类ScheduledThreadPoolExecutorTest{
静态ScheduledThreadPoolExecutor executor=新ScheduledThreadPoolExecutor(15);//否
静态调度未来t;
静态类MyTask实现Runnable{
私有int尝试=1;
公开募捐{
系统输出打印(尝试+“”);
如果(++尝试>5){
t、 取消(假);
}
}
}
公共静态void main(字符串[]args){
t=executor.scheduleAtFixedRate(newMyTask(),0,1,TimeUnit.SECONDS);
}
}
在线程外很好地取消:
public class ScheduleTest {
@Test
public void testCancel() throws Exception {
final ScheduledThreadPoolExecutor EXECUTOR = (ScheduledThreadPoolExecutor) Executors.newScheduledThreadPool(2);
ScheduledFuture f1 = EXECUTOR.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
System.out.println("Im alive 1");
}
}, 0, 1, TimeUnit.SECONDS);
ScheduledFuture f2 = EXECUTOR.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
System.out.println("Im alive 2");
}
}, 0, 2, TimeUnit.SECONDS);
Thread.sleep(10000);
f1.cancel(true);
System.out.println("f1 cancel");
Thread.sleep(10000);
f2.cancel(false);
System.out.println("f2 cancel");
Thread.sleep(10000);
}
}
有时线程不能被取消,这通常通过volatile boolean isCancelled解决;
CountDownLatch
是另一种方法。当线程完成时,在闩锁上调用countDown()
。调用线程调用闩锁。wait()
直到所有线程完成。此时调用ExecutorService.shutdownNow()
,以便主线程不会变成僵尸
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class ScheduledThreadPoolExecutorTest {
static int i = 0;
public static void main(String[] args) throws Exception {
final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
final CountDownLatch latch = new CountDownLatch(1);
executor.scheduleAtFixedRate(() -> {
System.out.println(++i);
if (i > 4) {
latch.countDown();
}
}, 0, 100, TimeUnit.MILLISECONDS);
latch.await();
executor.shutdownNow();
}
}
非常感谢!我确实知道scheduledfuture,但我尝试使用这种方式:t=executor.scheduleAtFixedRate(newmytask(),0,1,TimeUnit.SECONDS);t.cancel(true);由于明显的原因,这永远不会起作用。在任务实现中取消任务似乎是正确的。谢谢。这很有帮助。有趣的是,这个示例从不存在。我认为您需要执行器关闭,或者更确切地说,您需要一个t.get()
和CancellationException的catch块中的执行器关闭这种方法是线程安全的吗?任务执行可能会在分配到主线程之前到达t.cancel(),从而导致NullPointerException。这是一个很好的示例,因为它会面临很多问题……谢谢:)