ThreadPoolExecutor執行緒池的使用及原理

執行緒池原理：

package com.cy.java.api.thread;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
//JUC

public class ThreadPoolTests {
    public static void main(String[] args) {
    
    	//核心執行緒，核心執行緒滿了，放入佇列，佇列滿了開啟再新執行緒，
        int corePoolSize=2;
        
        //最大執行緒數（核心執行緒+新執行緒），最大執行緒數、佇列數都滿了，默認拋例外
        int maximumPoolSize=3;
        
        //執行緒池中空閑執行緒等待作業的超時時間
        int keepAliveTime=60;
        
        //時間顆粒度轉換(例如keepAliveTime默認單位為毫秒，轉換成秒)
        TimeUnit unit=TimeUnit.SECONDS;
        
        //任務佇列,存盤要執行的任務，最大佇列數設為1
        BlockingQueue<Runnable> workQueue=new ArrayBlockingQueue<>(1);
        
        //定義執行器
        RejectedExecutionHandler handler=
        //new ThreadPoolExecutor.AbortPolicy();//不能執行任務時，拋出例外
          new ThreadPoolExecutor.CallerRunsPolicy();//由呼叫者去執行

        //創建執行緒的工廠
        ThreadFactory threadFactory=new ThreadFactory() {
        	//定義執行緒名
            private String prefix="db-service-thread-";
            //生成自增長數
            private AtomicInteger atomicInteger=new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable task) {
                return new Thread(task,prefix+atomicInteger.incrementAndGet());
            }
        };

          
        //構建執行緒池物件
        ThreadPoolExecutor threadPool= new ThreadPoolExecutor(
                        corePoolSize,
                        maximumPoolSize,
                        keepAliveTime,
                        unit,
                        workQueue,
                        threadFactory,
                        handler);


//設定休眠時間測驗允許結果，核心執行緒數2，最大執行緒樹3，最大佇列1，超出最大限執行緒數時，由呼叫者去執行，
        threadPool.execute(new Runnable() {//task
            @Override
            public void run() {
                String tName=Thread.currentThread().getName();
                System.out.println(tName+"->execute->task1");
                try{Thread.sleep(5000);}catch (Exception e){}
            }
        });
        threadPool.execute(new Runnable() {//task
            @Override
            public void run() {
                String tName=Thread.currentThread().getName();
                System.out.println(tName+"->execute->task2");
                try{Thread.sleep(5000);}catch (Exception e){}
            }
        });
        threadPool.execute(new Runnable() {//task
            @Override
            public void run() {
                String tName=Thread.currentThread().getName();
                System.out.println(tName+"->execute->task3");
            }
        });
        threadPool.execute(new Runnable() {//task
            @Override
            public void run() {
                String tName=Thread.currentThread().getName();
                System.out.println(tName+"->execute->task4");
                try{Thread.sleep(5000);}catch (Exception e){}
            }
        });
        threadPool.execute(new Runnable() {//task
            @Override
            public void run() {
                String tName=Thread.currentThread().getName();
                System.out.println(tName+"->execute->task5");
                try{Thread.sleep(5000);}catch (Exception e){}
            }
        });

    }
}

/*運行結果：
db-service-thread-1->execute->task1
db-service-thread-2->execute->task2
db-service-thread-3->execute->task4
main->execute->task5
db-service-thread-2->execute->task3
*/

執行緒溢位時出錯：