Introduction to several implementation methods and differences of Java thread pool

Introduction to several implementation methods and differences of Java thread pool

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<Integer> customerList = new ArrayList<Integer>();
  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<Integer> customerList) {
  List<Callable<Integer>> listCallable = new ArrayList<Callable<Integer>>();
  for (int i = 0; i < 10; i++) {
   Callable<Integer> callable = new Callable<Integer>() {
    @Override
    public Integer call() throws Exception {
     return new Random().nextInt(10);
    }
   };
   listCallable.add(callable);
  }
  try {
   List<Future<Integer>> listFuture = service.invokeAll(listCallable);
   for (Future<Integer> 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<Integer> customerList) {
  List<Callable<List<Integer>>> listCallable = new ArrayList<Callable<List<Integer>>>();
  for (int i = 0; i < 10; i++) {
   Callable<List<Integer>> callable = new Callable<List<Integer>>() {
    @Override
    public List<Integer> call() throws Exception {
     List<Integer> 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<Future<List<Integer>>> listFuture = service.invokeAll(listCallable);
   for (Future<List<Integer>> future : listFuture) {
    List<Integer> list = future.get();
    customerList.addAll(list);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  System.out.println(customerList.toString());
 }
 
 public static void testCacheThreadPool(ExecutorService service, List<Integer> customerList) {
  List<Callable<List<Integer>>> listCallable = new ArrayList<Callable<List<Integer>>>();
  for (int i = 0; i < 10; i++) {
   Callable<List<Integer>> callable = new Callable<List<Integer>>() {
    @Override
    public List<Integer> call() throws Exception {
     List<Integer> 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<Future<List<Integer>>> listFuture = service.invokeAll(listCallable);
   for (Future<List<Integer>> future : listFuture) {
    List<Integer> list = future.get();
    customerList.addAll(list);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  System.out.println(customerList.toString());
 }
 
 public static void testFixedThreadPool(ExecutorService service, List<Integer> customerList) {
  List<Callable<List<Integer>>> listCallable = new ArrayList<Callable<List<Integer>>>();
  for (int i = 0; i < 10; i++) {
   Callable<List<Integer>> callable = new Callable<List<Integer>>() {
    @Override
    public List<Integer> call() throws Exception {
     List<Integer> 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<Future<List<Integer>>> listFuture = service.invokeAll(listCallable);
   for (Future<List<Integer>> future : listFuture) {
    List<Integer> list = future.get();
    customerList.addAll(list);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  System.out.println(customerList.toString());
 }
 
 public static List<Integer> getList(int x) {
  List<Integer> list = new ArrayList<Integer>();
  list.add(x);
  list.add(x * x);
  return list;
 }
}

Using: LinkedBlockingQueue to implement thread pool explanation

//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<Runnable>(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。

About: Explanation of several default implementations of RejectedExecutionHandler

//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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