【Java多线程系列七】ExecutorService
java.util.concurrent.ExecutorService接口提供了许多线程管理的方法
| Method | 说明 |
| shutdown | 拒绝接收新的任务，待已提交的任务执行后关闭，且宿主线程不阻塞，若需要阻塞可借助awaitTermination实现 |
| shutdownNow | 停止所有正在执行的任务，挂起未执行的任务并关闭，且宿主线程不阻塞，若需要阻塞可借助awaitTermination实现 |
| awaitTermination | 当发生shutdown时，阻塞宿主线程直到约定的时间已过或者所有任务完成 |
| submit | 提交任务Callable/Runnable，可利用Future的get()方法使宿主线程阻塞直到任务结束后返回结果 |
有了以上方法，便可以基于此接口实现线程池的各种功能(例如java.util.concurrent.ThreadPoolExecutor/java.util.concurrent.ScheduledThreadPoolExecutor)，以java.util.concurrent.ThreadPoolExecutor为例，其参数的详解
| Name | Type | 说明 |
| corePoolSize | int | 线程池中最小的线程数 |
| maximumPoolSize | int | 线程池中最大的线程数 |
| keepAliveTime | long | 线程空闲时间，若线程数大于corePoolSize，空闲时间超过该值的线程将被终止回收 |
| unit | TimeUnit | keepAliveTime的时间单位 |
| workQueue | BlockingQueue<Runnable> | 已提交但未执行的任务队列 |
| threadFactory | ThreadFactory | 创建新线程的工厂 |
| handler | RejectedExecutionHandler | 当线程池或队列达到上限拒绝新任务抛出异常时的处理类 |
同时，java.util.concurrent.Executors类提供的常用方法有
| Method | 说明 | 基类 |
| newFixedThreadPool | 线程池中含固定数量的线程 | 基于java.util.concurrent.ThreadPoolExecutor类 |
| newSingleThreadExecutor | 线程池中仅含一个工作线程 | |
| newCachedThreadPool | 按需创建线程，若线程池中无可用线程，则创建新的线程并加入，直到线程数达到上限值(Integer.MAX_VALUE) | |
| newWorkStealingPool | 按照可用CPU数创建线程池 | 基于java.util.concurrent.ForkJoinPool类 |
java.util.concurrent.ForkJoinPool类是Fork/Join框架的实现类，Fork/Join框架是Java7提供了的一个用于并行执行任务的框架， 是一个把大任务分割成若干个小任务，最终汇总每个小任务结果后得到大任务结果的框架，该类在有递归实现的场景有更优异的表现。
package com.concurrent.test;import java.util.Arrays;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import org.junit.Assert;
import org.junit.Test;
/**
* 测试ExecutorService
*/
public class ThreadExecutorServiceTest {
private static final String THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION = "This is shutdownWithAwaitTermination";
private static final int RESULT = 111;
private static boolean submitRunable() throws InterruptedException, ExecutionException {
ExecutorService executorService = Executors.newSingleThreadExecutor();
Future<?> future = executorService.submit(new Runnable() {
@Override
public void run() {
System.out.println("This is submitRunnable");
}
});
return future.get() == null;
}
private static Integer submitRunnableWithResult() throws InterruptedException, ExecutionException {
ExecutorService executorService = Executors.newSingleThreadExecutor();
Future<Integer> future = executorService.submit(new Runnable() {
@Override
public void run() {
System.out.println("This is submitRunnableWithResult");
}
}, RESULT);
return future.get();
}
private static Integer submitBlockCallable() throws InterruptedException, ExecutionException {
ExecutorService executorService = Executors.newSingleThreadExecutor();
Future<Integer> future = executorService.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
System.out.println("This is submitBlockCallable");
return RESULT;
}
});
return future.get(); //阻塞
}
private static boolean submitNonBlockCallable() {
ExecutorService executorService = Executors.newSingleThreadExecutor();
Future<Integer> future = executorService.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
System.out.println("This is submitNonBlockCallable");
return RESULT;
}
});
while (!future.isDone()) {// 非阻塞
System.out.println(new Date());
}
return future.isDone();
}
private static String shutdown() {
ExecutorService executorService = Executors.newSingleThreadExecutor();
final StringBuilder sb = new StringBuilder();
executorService.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
Thread.sleep(10000);
sb.append("This is shutdown");
return RESULT;
}
});
executorService.shutdown();
return sb.toString();
}
private static String shutdownWithAwaitTermination() throws InterruptedException {
ExecutorService executorService = Executors.newSingleThreadExecutor();
final StringBuilder sb = new StringBuilder();
executorService.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
Thread.sleep(10000);
sb.append(THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION);
return RESULT;
}
});
executorService.shutdown();
executorService.awaitTermination(Integer.MAX_VALUE, TimeUnit.DAYS);
return sb.toString();
}
private static int testForkJoinPool(List<Integer> list) throws InterruptedException, ExecutionException {
ForkJoinPool forkJoinPool = new ForkJoinPool(8);
Future<Integer> future = forkJoinPool.submit(new SumTask(list));
return future.get();
}
@Test
public void test() throws InterruptedException, ExecutionException {
Assert.assertTrue(submitRunable());
Assert.assertEquals(RESULT, submitRunnableWithResult().intValue());
Assert.assertEquals(RESULT, submitBlockCallable().intValue());
Assert.assertTrue(submitNonBlockCallable());
Assert.assertTrue(shutdown().isEmpty());
Assert.assertEquals(THIS_IS_SHUTDOWN_WITH_AWAIT_TERMINATION, shutdownWithAwaitTermination());
Assert.assertEquals(10, testForkJoinPool(Arrays.asList(new Integer[] { 1, 2, 3, 4 })));
Assert.assertEquals(49, testForkJoinPool(Arrays.asList(new Integer[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 })));
Assert.assertEquals(60, testForkJoinPool(Arrays.asList(new Integer[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 })));
}
}
SumTask类如下：
package com.concurrent.test;import java.util.List;
import java.util.concurrent.RecursiveTask;
public class SumTask extends RecursiveTask<Integer> {
/**
*
*/
private static final long serialVersionUID = -5468389855825594053L;
private List<Integer> list;
public SumTask(List<Integer> list) {
this.list = list;
}
/*
* Ensure it is necessary to divide the job to parts and finish them separately
*/
@Override
protected Integer compute() {
int rtn , size = list.size();
if (size < 10) {
rtn = sum(list);
}
else{
SumTask subTask1 = new SumTask(list.subList(0, size /2));
SumTask subTask2 = new SumTask(list.subList(size /2 + 1, size));
subTask1.fork();
subTask2.fork();
rtn = subTask1.join() + subTask2.join();
}
return rtn;
}
private int sum(List<Integer> list) {
int sum = 0;
for (Integer integer : list) {
sum += integer;
}
return sum;
}
}
以上是 【Java多线程系列七】ExecutorService 的全部内容， 来源链接： utcz.com/z/392775.html
