學(xué)生視角手把手帶你寫Java?線程池改良版

更新時(shí)間：2022年03月21日 11:16:23 作者：摸魚打醬油

作者是一個(gè)來自河源的大三在校生，以下筆記都是作者自學(xué)之路的一些淺薄經(jīng)驗(yàn)，如有錯(cuò)誤請(qǐng)指正，將來會(huì)不斷的完善筆記，幫助更多的Java愛好者入門

Java手寫線程池（第二代）

第二代線程池的優(yōu)化

1：新增了4種拒絕策略。分別為：MyAbortPolicy、MyDiscardPolicy、MyDiscardOldestPolicy、MyCallerRunsPolicy

2：對(duì)線程池MyThreadPoolExecutor的構(gòu)造方法進(jìn)行優(yōu)化，增加了參數(shù)校驗(yàn)，防止亂傳參數(shù)現(xiàn)象。

3：這是最重要的一個(gè)優(yōu)化。

移除線程池的線程預(yù)熱功能。因?yàn)榫€程預(yù)熱會(huì)極大的耗費(fèi)內(nèi)存，當(dāng)我們不用線程池時(shí)也會(huì)一直在運(yùn)行狀態(tài)。
換來的是在調(diào)用execute方法添加任務(wù)時(shí)通過檢查workers線程集合目前的大小與corePoolSize的值去比較，再通過new MyWorker()去創(chuàng)建添加線程到線程池，這樣好處就是當(dāng)我們創(chuàng)建線程池如果不使用的話則對(duì)當(dāng)前內(nèi)存沒有一點(diǎn)影響，當(dāng)使用了才會(huì)創(chuàng)建線程并放入線程池中進(jìn)行復(fù)用。

線程池構(gòu)造器

	public MyThreadPoolExecutor(){
        this(5,new ArrayBlockingQueue<>(10), Executors.defaultThreadFactory(),defaultHandle);
    }
    public MyThreadPoolExecutor(int corePoolSize, BlockingQueue<Runnable> waitingQueue,ThreadFactory threadFactory) {
        this(corePoolSize,waitingQueue,threadFactory,defaultHandle);
    }
    public MyThreadPoolExecutor(int corePoolSize, BlockingQueue<Runnable> waitingQueue,ThreadFactory threadFactory,MyRejectedExecutionHandle handle) {
        this.workers=new HashSet<>(corePoolSize);
        if(corePoolSize>=0&&waitingQueue!=null&&threadFactory!=null&&handle!=null){
            this.corePoolSize=corePoolSize;
            this.waitingQueue=waitingQueue;
            this.threadFactory=threadFactory;
            this.handle=handle;
        }else {
            throw new NullPointerException("線程池參數(shù)不合法");
        }
    }

線程池拒絕策略

策略接口：MyRejectedExecutionHandle

package com.springframework.concurrent;

/**
 * 自定義拒絕策略
 * @author 游政杰
 */
public interface MyRejectedExecutionHandle {

    void rejectedExecution(Runnable runnable,MyThreadPoolExecutor threadPoolExecutor);

}

策略內(nèi)部實(shí)現(xiàn)類

/**
     * 實(shí)現(xiàn)自定義拒絕策略
     */
    //拋異常策略（默認(rèn)）
    public static class MyAbortPolicy implements MyRejectedExecutionHandle{
        public MyAbortPolicy(){

        }
        @Override
        public void rejectedExecution(Runnable r, MyThreadPoolExecutor t) {
            throw new MyRejectedExecutionException("任務(wù)-> "+r.toString()+"被線程池-> "+t.toString()+" 拒絕");
        }
    }
    //默默丟棄策略
    public static class MyDiscardPolicy implements MyRejectedExecutionHandle{

        public MyDiscardPolicy() {
        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {

        }
    }
    //丟棄掉最老的任務(wù)策略
    public static class MyDiscardOldestPolicy implements MyRejectedExecutionHandle{
        public MyDiscardOldestPolicy() {
        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {
            if(!threadPoolExecutor.isShutdown()){ //如果線程池沒被關(guān)閉
                threadPoolExecutor.getWaitingQueue().poll();//丟掉最老的任務(wù)，此時(shí)就有位置當(dāng)新任務(wù)了
                threadPoolExecutor.execute(runnable); //把新任務(wù)加入到隊(duì)列中
            }
        }
    }
    //由調(diào)用者調(diào)用策略
    public static class MyCallerRunsPolicy implements MyRejectedExecutionHandle{
        public MyCallerRunsPolicy(){

        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {
            if(!threadPoolExecutor.isShutdown()){//判斷線程池是否被關(guān)閉
                runnable.run();
            }
        }
    }

封裝拒絕方法

    protected final void reject(Runnable runnable){
        this.handle.rejectedExecution(runnable, this);
    }

    protected final void reject(Runnable runnable,MyThreadPoolExecutor threadPoolExecutor){
        this.handle.rejectedExecution(runnable, threadPoolExecutor);
    }

execute方法

	@Override
    public boolean execute(Runnable runnable)
    {
        if (!this.waitingQueue.offer(runnable)) {
            this.reject(runnable);
            return false;
        }
        else {
            if(this.workers!=null&&this.workers.size()<corePoolSize){//這種情況才能添加線程
                MyWorker worker = new MyWorker(); //通過構(gòu)造方法添加線程
            }
            return true;
        }
    }

可以看出只有當(dāng)往線程池放任務(wù)時(shí)才會(huì)創(chuàng)建線程對(duì)象。

手寫線程池源碼

MyExecutorService

package com.springframework.concurrent;

import java.util.concurrent.BlockingQueue;

/**
 * 自定義線程池業(yè)務(wù)接口
 * @author 游政杰
 */
public interface MyExecutorService {

    boolean execute(Runnable runnable);

    void shutdown();

    void shutdownNow();

    boolean isShutdown();

    BlockingQueue<Runnable> getWaitingQueue();

}

MyRejectedExecutionException

package com.springframework.concurrent;

/**
 * 自定義拒絕異常
 */
public class MyRejectedExecutionException extends RuntimeException {

    public MyRejectedExecutionException() {
    }
    public MyRejectedExecutionException(String message) {
        super(message);
    }

    public MyRejectedExecutionException(String message, Throwable cause) {
        super(message, cause);
    }

    public MyRejectedExecutionException(Throwable cause) {
        super(cause);
    }

}

MyRejectedExecutionHandle

package com.springframework.concurrent;

/**
 * 自定義拒絕策略
 * @author 游政杰
 */
public interface MyRejectedExecutionHandle {

    void rejectedExecution(Runnable runnable,MyThreadPoolExecutor threadPoolExecutor);

}

核心類MyThreadPoolExecutor

package com.springframework.concurrent;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 純手?jǐn)]線程池框架
 * @author 游政杰
 */
public class MyThreadPoolExecutor implements MyExecutorService{

    private static final AtomicInteger taskcount=new AtomicInteger(0);//執(zhí)行任務(wù)次數(shù)
    private static final AtomicInteger threadNumber=new AtomicInteger(0); //線程編號(hào)
    private static volatile int corePoolSize; //核心線程數(shù)
    private final HashSet<MyWorker> workers; //工作線程
    private final BlockingQueue<Runnable> waitingQueue; //等待隊(duì)列
    private static final String THREADPOOL_NAME="MyThread-Pool-";//線程名稱
    private volatile boolean isRunning=true; //是否運(yùn)行
    private volatile boolean STOPNOW=false; //是否立刻停止
    private volatile ThreadFactory threadFactory; //線程工廠
    private static final MyRejectedExecutionHandle defaultHandle=new MyThreadPoolExecutor.MyAbortPolicy();//默認(rèn)拒絕策略
    private volatile MyRejectedExecutionHandle handle; //拒絕紫略

    public MyThreadPoolExecutor(){
        this(5,new ArrayBlockingQueue<>(10), Executors.defaultThreadFactory(),defaultHandle);
    }
    public MyThreadPoolExecutor(int corePoolSize, BlockingQueue<Runnable> waitingQueue,ThreadFactory threadFactory) {
        this(corePoolSize,waitingQueue,threadFactory,defaultHandle);
    }
    public MyThreadPoolExecutor(int corePoolSize, BlockingQueue<Runnable> waitingQueue,ThreadFactory threadFactory,MyRejectedExecutionHandle handle) {
        this.workers=new HashSet<>(corePoolSize);
        if(corePoolSize>=0&&waitingQueue!=null&&threadFactory!=null&&handle!=null){
            this.corePoolSize=corePoolSize;
            this.waitingQueue=waitingQueue;
            this.threadFactory=threadFactory;
            this.handle=handle;
        }else {
            throw new NullPointerException("線程池參數(shù)不合法");
        }
    }
    /**
     * 實(shí)現(xiàn)自定義拒絕策略
     */
    //拋異常策略（默認(rèn)）
    public static class MyAbortPolicy implements MyRejectedExecutionHandle{
        public MyAbortPolicy(){

        }
        @Override
        public void rejectedExecution(Runnable r, MyThreadPoolExecutor t) {
            throw new MyRejectedExecutionException("任務(wù)-> "+r.toString()+"被線程池-> "+t.toString()+" 拒絕");
        }
    }
    //默默丟棄策略
    public static class MyDiscardPolicy implements MyRejectedExecutionHandle{

        public MyDiscardPolicy() {
        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {

        }
    }
    //丟棄掉最老的任務(wù)策略
    public static class MyDiscardOldestPolicy implements MyRejectedExecutionHandle{
        public MyDiscardOldestPolicy() {
        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {
            if(!threadPoolExecutor.isShutdown()){ //如果線程池沒被關(guān)閉
                threadPoolExecutor.getWaitingQueue().poll();//丟掉最老的任務(wù)，此時(shí)就有位置當(dāng)新任務(wù)了
                threadPoolExecutor.execute(runnable); //把新任務(wù)加入到隊(duì)列中
            }
        }
    }
    //由調(diào)用者調(diào)用策略
    public static class MyCallerRunsPolicy implements MyRejectedExecutionHandle{
        public MyCallerRunsPolicy(){

        }
        @Override
        public void rejectedExecution(Runnable runnable, MyThreadPoolExecutor threadPoolExecutor) {
            if(!threadPoolExecutor.isShutdown()){//判斷線程池是否被關(guān)閉
                runnable.run();
            }
        }
    }
    //call拒絕方法
    protected final void reject(Runnable runnable){
        this.handle.rejectedExecution(runnable, this);
    }

    protected final void reject(Runnable runnable,MyThreadPoolExecutor threadPoolExecutor){
        this.handle.rejectedExecution(runnable, threadPoolExecutor);
    }

    /**
     * MyWorker就是我們每一個(gè)線程對(duì)象
     */
    private final class MyWorker implements Runnable{

        final Thread thread; //為每個(gè)MyWorker

        MyWorker(){
            Thread td = threadFactory.newThread(this);
            td.setName(THREADPOOL_NAME+threadNumber.getAndIncrement());
            this.thread=td;
            this.thread.start();
            workers.add(this);
        }

        //執(zhí)行任務(wù)
        @Override
        public void run() {
            //循環(huán)接收任務(wù)
                while (true)
                {
                    //循環(huán)退出條件：
                    //1：當(dāng)isRunning為false并且waitingQueue的隊(duì)列大小為0（也就是無任務(wù)了），會(huì)優(yōu)雅的退出。
                    //2：當(dāng)STOPNOW為true，則說明調(diào)用了shutdownNow方法進(jìn)行暴力退出。
                    if((!isRunning&&waitingQueue.size()==0)||STOPNOW)
                    {
                        break;
                    }else {
                        //不斷取任務(wù)，當(dāng)任務(wù)！=null時(shí)則調(diào)用run方法處理任務(wù)
                        Runnable runnable = waitingQueue.poll();
                        if(runnable!=null){
                            runnable.run();
                            System.out.println("task==>"+taskcount.incrementAndGet());
                        }
                    }
                }
        }
    }

    //往線程池中放任務(wù)
    @Override
    public boolean execute(Runnable runnable)
    {
        if (!this.waitingQueue.offer(runnable)) {
            this.reject(runnable);
            return false;
        }
        else {
            if(this.workers!=null&&this.workers.size()<corePoolSize){//這種情況才能添加線程
                MyWorker worker = new MyWorker(); //通過構(gòu)造方法添加線程
            }
            return true;
        }
    }
    //優(yōu)雅的關(guān)閉
    @Override
    public void shutdown()
    {
        this.isRunning=false;
    }
    //暴力關(guān)閉
    @Override
    public void shutdownNow()
    {
        this.STOPNOW=true;
    }

    //判斷線程池是否關(guān)閉
    @Override
    public boolean isShutdown() {
        return !this.isRunning||STOPNOW;
    }

    //獲取等待隊(duì)列
    @Override
    public BlockingQueue<Runnable> getWaitingQueue() {
        return this.waitingQueue;
    }
}

線程池測(cè)試類

package com.springframework.test;

import com.springframework.concurrent.MyThreadPoolExecutor;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;

public class ThreadPoolTest {

  public static void main(String[] args) {


//      MyThreadPoolExecutor myThreadPoolExecutor = new MyThreadPoolExecutor
//              (5,new ArrayBlockingQueue<>(6), Executors.defaultThreadFactory(),new MyThreadPoolExecutor.MyAbortPolicy());

//      MyThreadPoolExecutor myThreadPoolExecutor = new MyThreadPoolExecutor
//              (5,new ArrayBlockingQueue<>(6), Executors.defaultThreadFactory(),new MyThreadPoolExecutor.MyDiscardPolicy());

//      MyThreadPoolExecutor myThreadPoolExecutor = new MyThreadPoolExecutor
//              (5,new ArrayBlockingQueue<>(6), Executors.defaultThreadFactory(),new MyThreadPoolExecutor.MyDiscardOldestPolicy());

      MyThreadPoolExecutor myThreadPoolExecutor = new MyThreadPoolExecutor
              (5,new ArrayBlockingQueue<>(6), Executors.defaultThreadFactory(),new MyThreadPoolExecutor.MyCallerRunsPolicy());


      for(int i=0;i<11;i++){

          int finalI = i;
          myThreadPoolExecutor.execute(()->{
              System.out.println(Thread.currentThread().getName()+">>>>"+ finalI);
          });

      }

      myThreadPoolExecutor.shutdown();

//      myThreadPoolExecutor.shutdownNow();




  }
}

好了第二代線程池就優(yōu)化到這了，后面可能還會(huì)出第三代，不斷進(jìn)行優(yōu)化。

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