java并发编程-限时任务
来源：互联网 发布：wampserver域名重定向 编辑：程序博客网 时间：2024/04/28 10:29
原文地址：http://blog.csdn.net/aitangyong/article/details/38172189
ExecutorService是JDK并发工具包提供的一个核心接口，相当于一个线程池，提供执行任务和管理生命周期的方法。ExecutorService接口中的大部分API都是比较容易上手使用的，本文主要介绍下invokeAll和invokeAll方法的特性和使用。我们先提供几个任务类:一个耗时任务，一个异常任务，一个短时任务。他们会在接下来的测试代码中使用。
[java] view plaincopyprint?
package tasks;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
public class SleepSecondsCallable implements Callable<String>
{
private String name;
private int seconds;
public SleepSecondsCallable(String name, int seconds)
{
this.name = name;
this.seconds = seconds;
}
public String call() throws Exception
{
System.out.println(name + ",begin to execute");
try
{
TimeUnit.SECONDS.sleep(seconds);
} catch (InterruptedException e)
{
System.out.println(name + " was disturbed during sleeping.");
e.printStackTrace();
return name + "_SleepSecondsCallable_failed";
}
System.out.println(name + ",success to execute");
return name + "_SleepSecondsCallable_succes";
}
}
package tasks;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
public class SleepSecondsCallable implements Callable<String>
{
private String name;
private int seconds;
public SleepSecondsCallable(String name, int seconds)
{
this.name = name;
this.seconds = seconds;
}
public String call() throws Exception
{
System.out.println(name + ",begin to execute");
try
{
TimeUnit.SECONDS.sleep(seconds);
} catch (InterruptedException e)
{
System.out.println(name + " was disturbed during sleeping.");
e.printStackTrace();
return name + "_SleepSecondsCallable_failed";
}
System.out.println(name + ",success to execute");
return name + "_SleepSecondsCallable_succes";
}
}
这是一个通过睡眠来模拟的耗时任务，该任务是可中断/可终止的任务，能够响应中断请求。
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package tasks;
import java.util.concurrent.Callable;
public class ExceptionCallable implements Callable<String>
{
private String name = null;
public ExceptionCallable()
{
}
public ExceptionCallable(String name)
{
this.name = name;
}
@Override
public String call() throws Exception
{
System.out.println("begin to ExceptionCallable.");
System.out.println(name.length());
System.out.println("end to ExceptionCallable.");
return name;
}
}
package tasks;
import java.util.concurrent.Callable;
public class ExceptionCallable implements Callable<String>
{
private String name = null;
public ExceptionCallable()
{
}
public ExceptionCallable(String name)
{
this.name = name;
}
@Override
public String call() throws Exception
{
System.out.println("begin to ExceptionCallable.");
System.out.println(name.length());
System.out.println("end to ExceptionCallable.");
return name;
}
}
这是一个可能会在执行过程中，抛出空指针异常的任务。
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package tasks;
import java.util.Random;
import java.util.concurrent.Callable;
public class RandomTenCharsTask implements Callable<String>
{
@Override
public String call() throws Exception
{
System.out.println("RandomTenCharsTask begin to execute...");
StringBuffer content = new StringBuffer();
String base = "abcdefghijklmnopqrstuvwxyz0123456789";
Random random = new Random();
for (int i = 0; i < 10; i++)
{
int number = random.nextInt(base.length());
content.append(base.charAt(number));
}
System.out.println("RandomTenCharsTask complete.result=" + content);
return content.toString();
}
}
package tasks;
import java.util.Random;
import java.util.concurrent.Callable;
public class RandomTenCharsTask implements Callable<String>
{
@Override
public String call() throws Exception
{
System.out.println("RandomTenCharsTask begin to execute...");
StringBuffer content = new StringBuffer();
String base = "abcdefghijklmnopqrstuvwxyz0123456789";
Random random = new Random();
for (int i = 0; i < 10; i++)
{
int number = random.nextInt(base.length());
content.append(base.charAt(number));
}
System.out.println("RandomTenCharsTask complete.result=" + content);
return content.toString();
}
}
这是一个正常的短时的任务，产生10个随机字符组成的字符串。
1.测试invokeAny()
第一种情况，向线程池提交2个耗时任务SleepSecondsCallable
[java] view plaincopyprint?
/**
* 提交的任务集合,一旦有1个任务正常完成(没有抛出异常),会终止其他未完成的任务
*/
public static void invokeAny1() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 1));
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}
/**
* 提交的任务集合,一旦有1个任务正常完成(没有抛出异常),会终止其他未完成的任务
*/
public static void invokeAny1() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 1));
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}程序的执行结果是：返回t2线程的执行结果t2_SleepSecondsCallable_succes，同时t1抛出java.lang.InterruptedException: sleep interrupted。
也就说：一旦有1个任务正常完成(执行过程中没有抛异常)，线程池会终止其他未完成的任务。
第二种情况，向线程池提交3个异常任务ExceptionCallable
[java] view plaincopyprint?
/**
* 没有1个正常完成的任务,invokeAny()方法抛出ExecutionException,封装了任务中元素的异常
*
*/
public static void invokeAny2() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}
/**
* 没有1个正常完成的任务,invokeAny()方法抛出ExecutionException,封装了任务中元素的异常
*
*/
public static void invokeAny2() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}程序执行结果是：调用invokeAny()报错 java.util.concurrent.ExecutionException: java.lang.NullPointerException。
也就是说：如果提交的任务列表中，没有1个正常完成的任务，那么调用invokeAny会抛异常，究竟抛的是哪儿个任务的异常，无关紧要。
第三种情况：先提交3个异常任务，再提交1个正常的耗时任务
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/**
* 有异常的任务,有正常的任务,invokeAny()不会抛异常,返回最先正常完成的任务
*/
public static void invokeAny3() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new SleepSecondsCallable("t1", 2));
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}
/**
* 有异常的任务,有正常的任务,invokeAny()不会抛异常,返回最先正常完成的任务
*/
public static void invokeAny3() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new SleepSecondsCallable("t1", 2));
String result = executorService.invokeAny(tasks);
System.out.println("result=" + result);
executorService.shutdown();
}程序执行结果是：不会抛出任何异常，打印出t2任务的返回结果。也就是说：invokeAny()和任务的提交顺序无关，只是返回最早正常执行完成的任务。
第四种情况，测试下使用限时版本的invokeAny()，主要功能与不限时版本的差别不大
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/**
* 还没有到超时之前,所以的任务都已经异常完成,抛出ExecutionException<br>
* 如果超时前满,还没有没有完成的任务,抛TimeoutException
*/
public static void invokeAnyTimeout() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
String result = executorService.invokeAny(tasks, 2, TimeUnit.SECONDS);
System.out.println("result=" + result);
executorService.shutdown();
}
/**
* 还没有到超时之前,所以的任务都已经异常完成,抛出ExecutionException<br>
* 如果超时前满,还没有没有完成的任务,抛TimeoutException
*/
public static void invokeAnyTimeout() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(3);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
tasks.add(new ExceptionCallable());
String result = executorService.invokeAny(tasks, 2, TimeUnit.SECONDS);
System.out.println("result=" + result);
executorService.shutdown();
}程序执行结果是：抛出ExecutionException。这个其实很合理，也很好理解。如果在超时之前，所有任务已经都是异常终止，那就没有必要在等下去了；如果超时之后，仍然有正在运行或等待运行的任务，那么会抛出TimeoutException。
最后我们来看下,JDK源码中ExecutorService.invokeAny的方法签名和注释
[java] view plaincopyprint?
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do. Upon normal or exceptional return,
* tasks that have not completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks or any of its elements
* are <tt>null</tt>
* @throws IllegalArgumentException if tasks is empty
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do. Upon normal or exceptional return,
* tasks that have not completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks or any of its elements
* are <tt>null</tt>
* @throws IllegalArgumentException if tasks is empty
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;与我们测试结果一致，invokeAny()返回最先正常完成(without throwing exception)的任务直接结果；一旦有任务正常完成或者调用出现异常，线程池都会终止正在运行或等待运行(tasks that have not completed are cancelled)的任务。
2.测试invokeAll()
这个方法相对来说比较好理解，就是执行任务列表中的所有任务，并返回与每个任务对应的Futue。也就是说，任务彼此之间不会相互影响，可以通过future跟踪每一个任务的执行情况，比如是否被取消，是正常完成，还是异常完成，这主要使用Future类提供的API。
[java] view plaincopyprint?
public static void testInvokeAll() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(5);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new RandomTenCharsTask());
tasks.add(new ExceptionCallable());
// 调用该方法的线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
List<Future<String>> results = executorService.invokeAll(tasks);
// 任务列表中所有任务执行完毕,才能执行该语句
System.out.println("wait for the result." + results.size());
executorService.shutdown();
for (Future<String> f : results)
{
// isCanceled=false,isDone=true
System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
+ f.isDone());
// ExceptionCallable任务会报ExecutionException
System.out.println("task result=" + f.get());
}
}
public static void testInvokeAll() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(5);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new RandomTenCharsTask());
tasks.add(new ExceptionCallable());
// 调用该方法的线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
List<Future<String>> results = executorService.invokeAll(tasks);
// 任务列表中所有任务执行完毕,才能执行该语句
System.out.println("wait for the result." + results.size());
executorService.shutdown();
for (Future<String> f : results)
{
// isCanceled=false,isDone=true
System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
+ f.isDone());
// ExceptionCallable任务会报ExecutionException
System.out.println("task result=" + f.get());
}
}程序的执行结果和一些结论，已经直接写在代码注释里面了。invokeAll是一个阻塞方法，会等待任务列表中的所有任务都执行完成。不管任务是正常完成，还是异常终止，Future.isDone()始终返回true。通过Future.isCanceled()可以判断任务是否在执行的过程中被取消。通过Future.get()可以获取任务的返回结果，或者是任务在执行中抛出的异常。
第二种情况，测试限时版本的invokeAll(Collection<? extends Callable<T>> tasks,long timeout, TimeUnit unit)
[java] view plaincopyprint?
/**
* 可以通过Future.isCanceled()判断任务是被取消,还是完成(正常/异常)<br>
* Future.isDone()总是返回true,对于invokeAll()的调用者来说,没有啥用
*/
public static void testInvokeAllTimeout() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(5);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new SleepSecondsCallable("t3", 3));
tasks.add(new RandomTenCharsTask());
List<Future<String>> results = executorService.invokeAll(tasks, 1,
TimeUnit.SECONDS);
System.out.println("wait for the result." + results.size());
for (Future<String> f : results)
{
System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
+ f.isDone());
}
executorService.shutdown();
}
/**
* 可以通过Future.isCanceled()判断任务是被取消,还是完成(正常/异常)<br>
* Future.isDone()总是返回true,对于invokeAll()的调用者来说,没有啥用
*/
public static void testInvokeAllTimeout() throws Exception
{
ExecutorService executorService = Executors.newFixedThreadPool(5);
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new SleepSecondsCallable("t3", 3));
tasks.add(new RandomTenCharsTask());
List<Future<String>> results = executorService.invokeAll(tasks, 1,
TimeUnit.SECONDS);
System.out.println("wait for the result." + results.size());
for (Future<String> f : results)
{
System.out.println("isCanceled=" + f.isCancelled() + ",isDone="
+ f.isDone());
}
executorService.shutdown();
}执行结果是：
wait for the result.4
isCanceled=true,isDone=true
isCanceled=true,isDone=true
isCanceled=true,isDone=true
isCanceled=false,isDone=true
也就是说给定的超时期满，还没有完成的任务会被取消，即Future.isCancelled()返回true；在超时期之前，无论是正常完成还是异常终止的任务，Future.isCancelled()返回false。
第三种情况，测试在等待invokeAll执行完成之前，线程被中断。
[java] view plaincopyprint?
/**
* 如果线程在等待invokeAll()执行完成的时候,被中断,会抛出InterruptedException<br>
* 此时线程池会终止没有完成的任务,这主要是为了减少资源的浪费.
*/
public static void testInvokeAllWhenInterrupt() throws Exception
{
final ExecutorService executorService = Executors.newFixedThreadPool(5);
// 调用invokeAll的线程
Thread invokeAllThread = new Thread() {
@Override
public void run()
{
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new RandomTenCharsTask());
// 调用线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
try
{
List<Future<String>> results = executorService
.invokeAll(tasks);
System.out.println("wait for the result." + results.size());
} catch (InterruptedException e)
{
System.out
.println("I was wait,but my thread was interrupted.");
e.printStackTrace();
}
}
};
invokeAllThread.start();
Thread.sleep(200);
invokeAllThread.interrupt();
executorService.shutdown();
}
/**
* 如果线程在等待invokeAll()执行完成的时候,被中断,会抛出InterruptedException<br>
* 此时线程池会终止没有完成的任务,这主要是为了减少资源的浪费.
*/
public static void testInvokeAllWhenInterrupt() throws Exception
{
final ExecutorService executorService = Executors.newFixedThreadPool(5);
// 调用invokeAll的线程
Thread invokeAllThread = new Thread() {
@Override
public void run()
{
List<Callable<String>> tasks = new ArrayList<Callable<String>>();
tasks.add(new SleepSecondsCallable("t1", 2));
tasks.add(new SleepSecondsCallable("t2", 2));
tasks.add(new RandomTenCharsTask());
// 调用线程会阻塞,直到tasks全部执行完成(正常完成/异常退出)
try
{
List<Future<String>> results = executorService
.invokeAll(tasks);
System.out.println("wait for the result." + results.size());
} catch (InterruptedException e)
{
System.out
.println("I was wait,but my thread was interrupted.");
e.printStackTrace();
}
}
};
invokeAllThread.start();
Thread.sleep(200);
invokeAllThread.interrupt();
executorService.shutdown();
}invokeAllThread 线程调用了ExecutorService.invokeAll()，在等待任务执行完成的时候，invokeAllThread被别的线程中断了。这个时候，
ExecutorService.invokeAll()会抛出java.lang.InterruptedException，任务t1和t2都被终止抛出java.lang.InterruptedException: sleep interrupted。
也就是说一旦ExecutorService.invokeAll()方法产生了异常，线程池中还没有完成的任务会被取消执行。
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