Java线程池的几种实现方法和区别介绍

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class TestThreadPool {
// -newFixedThreadPool与cacheThreadPool差不多，也是能reuse就用，但不能随时建新的线程
// -其独特之处:任意时间点，最多只能有固定数目的活动线程存在，此时如果有新的线程要建立，只能放在另外的队列中等待，直到当前的线程中某个线程终止直接被移出池子
// -和cacheThreadPool不同，FixedThreadPool没有IDLE机制(可能也有，但既然文档没提，肯定非常长，类似依赖上层的TCP或UDP
// IDLE机制之类的)，所以FixedThreadPool多数针对一些很稳定很固定的正规并发线程，多用于服务器
// -从方法的源代码看，cache池和fixed 池调用的是同一个底层池，只不过参数不同:
// fixed池线程数固定，并且是0秒IDLE(无IDLE)
// cache池线程数支持0-Integer.MAX_VALUE(显然完全没考虑主机的资源承受能力)，60秒IDLE
private static ExecutorService fixedService = Executors.newFixedThreadPool(6);
// -缓存型池子，先查看池中有没有以前建立的线程，如果有，就reuse.如果没有，就建一个新的线程加入池中
// -缓存型池子通常用于执行一些生存期很短的异步型任务
// 因此在一些面向连接的daemon型SERVER中用得不多。
// -能reuse的线程，必须是timeout IDLE内的池中线程，缺省timeout是60s,超过这个IDLE时长，线程实例将被终止及移出池。
// 注意，放入CachedThreadPool的线程不必担心其结束，超过TIMEOUT不活动，其会自动被终止。
private static ExecutorService cacheService = Executors.newCachedThreadPool();
// -单例线程，任意时间池中只能有一个线程
// -用的是和cache池和fixed池相同的底层池，但线程数目是1-1,0秒IDLE(无IDLE)
private static ExecutorService singleService = Executors.newSingleThreadExecutor();
// -调度型线程池
// -这个池子里的线程可以按schedule依次delay执行，或周期执行
private static ExecutorService scheduledService = Executors.newScheduledThreadPool(10);
public static void main(String[] args) {
DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
List customerList = new ArrayList();
System.out.println(format.format(new Date()));
testFixedThreadPool(fixedService, customerList);
System.out.println("--------------------------");
testFixedThreadPool(fixedService, customerList);
fixedService.shutdown();
System.out.println(fixedService.isShutdown());
System.out.println("----------------------------------------------------");
testCacheThreadPool(cacheService, customerList);
System.out.println("----------------------------------------------------");
testCacheThreadPool(cacheService, customerList);
cacheService.shutdownNow();
System.out.println("----------------------------------------------------");
testSingleServiceThreadPool(singleService, customerList);
testSingleServiceThreadPool(singleService, customerList);
singleService.shutdown();
System.out.println("----------------------------------------------------");
testScheduledServiceThreadPool(scheduledService, customerList);
testScheduledServiceThreadPool(scheduledService, customerList);
scheduledService.shutdown();
}
public static void testScheduledServiceThreadPool(ExecutorService service, List customerList) {
List> listCallable = new ArrayList>();
for (int i = 0; i < 10; i++) {
Callable callable = new Callable() {
@Override
public Integer call() throws Exception {
return new Random().nextInt(10);
}
};
listCallable.add(callable);
}
try {
List> listFuture = service.invokeAll(listCallable);
for (Future future : listFuture) {
Integer id = future.get();
customerList.add(id);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(customerList.toString());
}
public static void testSingleServiceThreadPool(ExecutorService service, List customerList) {
List>> listCallable = new ArrayList>>();
for (int i = 0; i < 10; i++) {
Callable> callable = new Callable>() {
@Override
public List call() throws Exception {
List list = getList(new Random().nextInt(10));
boolean isStop = false;
while (list.size() > 0 && !isStop) {
System.out.println(Thread.currentThread().getId() + " -- sleep:1000");
isStop = true;
}
return list;
}
};
listCallable.add(callable);
}
try {
List>> listFuture = service.invokeAll(listCallable);
for (Future> future : listFuture) {
List list = future.get();
customerList.addAll(list);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(customerList.toString());
}
public static void testCacheThreadPool(ExecutorService service, List customerList) {
List>> listCallable = new ArrayList>>();
for (int i = 0; i < 10; i++) {
Callable> callable = new Callable>() {
@Override
public List call() throws Exception {
List list = getList(new Random().nextInt(10));
boolean isStop = false;
while (list.size() > 0 && !isStop) {
System.out.println(Thread.currentThread().getId() + " -- sleep:1000");
isStop = true;
}
return list;
}
};
listCallable.add(callable);
}
try {
List>> listFuture = service.invokeAll(listCallable);
for (Future> future : listFuture) {
List list = future.get();
customerList.addAll(list);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(customerList.toString());
}
public static void testFixedThreadPool(ExecutorService service, List customerList) {
List>> listCallable = new ArrayList>>();
for (int i = 0; i < 10; i++) {
Callable> callable = new Callable>() {
@Override
public List call() throws Exception {
List list = getList(new Random().nextInt(10));
boolean isStop = false;
while (list.size() > 0 && !isStop) {
System.out.println(Thread.currentThread().getId() + " -- sleep:1000");
isStop = true;
}
return list;
}
};
listCallable.add(callable);
}
try {
List>> listFuture = service.invokeAll(listCallable);
for (Future> future : listFuture) {
List list = future.get();
customerList.addAll(list);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(customerList.toString());
}
public static List getList(int x) {
List list = new ArrayList();
list.add(x);
list.add(x * x);
return list;
}
}
使用：LinkedBlockingQueue实现线程池讲解
//例如：corePoolSize=3,maximumPoolSize=6,LinkedBlockingQueue(10)
//RejectedExecutionHandler默认处理方式是：ThreadPoolExecutor.AbortPolicy
//ThreadPoolExecutor executorService = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, 1L, TimeUnit.SECONDS, new LinkedBlockingQueue(10));
//1.如果线程池中(也就是调用executorService.execute)运行的线程未达到LinkedBlockingQueue.init(10)的话，当前执行的线程数是:corePoolSize(3)
//2.如果超过了LinkedBlockingQueue.init(10)并且超过的数>=init(10)+corePoolSize(3)的话，并且小于init(10)+maximumPoolSize. 当前启动的线程数是：(当前线程数-init(10))
//3.如果调用的线程数超过了init(10)+maximumPoolSize 则根据RejectedExecutionHandler的规则处理。
关于：RejectedExecutionHandler几种默认实现讲解
//默认使用：ThreadPoolExecutor.AbortPolicy，处理程序遭到拒绝将抛出运行时RejectedExecutionException。
RejectedExecutionHandler policy=new ThreadPoolExecutor.AbortPolicy();
在 ThreadPoolExecutor.CallerRunsPolicy 中，线程调用运行该任务的execute本身。此策略提供简单的反馈控制机制，能够减缓新任务的提交速度。
//policy=new ThreadPoolExecutor.CallerRunsPolicy();
在 ThreadPoolExecutor.DiscardPolicy 中，不能执行的任务将被删除。
//policy=new ThreadPoolExecutor.DiscardPolicy();
在 ThreadPoolExecutor.DiscardOldestPolicy 中，如果执行程序尚未关闭，则位于工作队列头部的任务将被删除，然后重试执行程序(如果再次失败，则重复此过程)。
//policy=new ThreadPoolExecutor.DiscardOldestPolicy();

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