ThreadLocal＆Fork/Join

ThreadLocal

One 、 Solve thread security issues .

Two 、ThreadLocal Principle

set()  Within the scope of the current thread , Set a value to store in ThreadLocal in , This value is only visible to the current thread . It is equivalent to establishing a copy within the scope of the current thread .

get()  Remove from the scope of the current thread set Value set by method .

remove()  Remove the value stored in the current thread

withInitial java8 Initialization method in

If the current value corresponds to entry Array key by null, Then the method will look forward to find that there are still key Invalid entry, Clean up . Through linear exploration , solve hash The question of conflict .

3、 ... and 、ThreadLocal actual combat

package com.gupaoedu.concurrent;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
public class ThreadLocalDemo {
    // Non thread safe 
    private static final SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    private static ThreadLocal<DateFormat> dateFormatThreadLocal=new ThreadLocal<>();

    private static DateFormat getDateFormat(){
        DateFormat dateFormat=dateFormatThreadLocal.get(); // Get a... From the scope of the current thread DateFormat
        if(dateFormat==null){
            dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            //Thread.currentThread();
            dateFormatThreadLocal.set(dateFormat); // To set a... Within the scope of the current thread simpleDateFormat object .
        }
        return dateFormat;
    }
    public static Date parse(String strDate) throws ParseException {
        return getDateFormat().parse(strDate);
    }

    public static void main(String[] args) {
        ExecutorService executorService= Executors.newFixedThreadPool(10);
        for (int i = 0; i < 20; i++) {
            executorService.execute(()->{
                try {
                    System.out.println(parse("2021-05-30 20:12:20"));
                } catch (ParseException e) {
                    e.printStackTrace();
                }
            });

        }
    }
}

 

Four 、 Memory leaks ：

Through the above analysis , We know expungeStaleEntry() The way is to help recycle , According to the source code , We can find out get and set Methods can trigger cleanup methods expungeStaleEntry(), So under normal circumstances, there will be no memory overflow But if we don't call get and set You may be faced with a memory overflow , Make a good habit of calling when you no longer use it remove(), Speed up garbage collection , Avoid memory overflow

Step back , Even if we don't call get and set and remove Method , At the end of the thread , There is no strong reference pointing to ThreadLocal Medium ThreadLocalMap 了 , such ThreadLocalMap And the elements inside will also be recycled , But there is a danger that , If a thread is thread pool , It doesn't end when the thread finishes executing the code , Just return it to the thread pool , This is the time ThreadLocalMap And the elements inside will not be recycled .

Fork/Join

One 、 Work flow chart

The top-level task in the figure uses submit The method is submitted to Fork/Join In the frame ,Fork/Join Put this task into a thread to run , In the work task compute The code of the method starts on this task T1 Analyze . If the number range that the current task needs to accumulate is too large （ What is set in the code is greater than 200）, Then the computing task is divided into two subtasks （T1.1 and T1.2）, Each subtask is responsible for calculating half of the data accumulation , See... In the code fork Method . If the number range to be accumulated in the current subtask is small enough （ Less than or equal to 200）, Just add up and return to the upper task .

Two 、ForkJoin actual combat

See the code below ：

 Entity class ： Comment on 、 goods 、 sales 、 The store 

package com.example.springbootforkjoin.pojo;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *  Comment information 
 **/
public class Comment {
    private String name;
    private String content;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

package com.example.springbootforkjoin.pojo;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *  Commodity information 
 **/
public class Item {

    private String productName;
    private int num;

    public String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }
}


package com.example.springbootforkjoin.pojo;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *  Sales information 
 **/

public class Seller {
    private int totalNum;
    private int sellerNum;

    public int getTotalNum() {
        return totalNum;
    }

    public void setTotalNum(int totalNum) {
        this.totalNum = totalNum;
    }

    public int getSellerNum() {
        return sellerNum;
    }

    public void setSellerNum(int sellerNum) {
        this.sellerNum = sellerNum;
    }
}


package com.example.springbootforkjoin.pojo;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *  Store information 
 **/
public class Shop {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Comment;
import com.example.springbootforkjoin.pojo.Item;
import com.example.springbootforkjoin.pojo.Seller;
import com.example.springbootforkjoin.pojo.Shop;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *  Aggregated entity classes 
 **/
public class Context {

    private Item item;  // goods 
    private Comment comment; // Comment on 
    private Seller seller; // Sales information 
    private Shop shop;  // Store information 

    public Item getItem() {
        return item;
    }

    public void setItem(Item item) {
        this.item = item;
    }

    public Comment getComment() {
        return comment;
    }

    public void setComment(Comment comment) {
        this.comment = comment;
    }

    public Seller getSeller() {
        return seller;
    }

    public void setSeller(Seller seller) {
        this.seller = seller;
    }

    public Shop getShop() {
        return shop;
    }

    public void setShop(Shop shop) {
        this.shop = shop;
    }

    @Override
    public String toString() {
        return "Context{" +
                "item=" + item +
                ", comment=" + comment +
                ", seller=" + seller +
                ", shop=" + shop +
                '}';
    }
}

 Corresponding service
package com.example.springbootforkjoin;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
public interface ILoadDataProcessor {


    /**
     *  Load the corresponding data 
     * @param context
     */
    void load(Context context);
}


package com.example.springbootforkjoin;

import java.util.concurrent.RecursiveAction;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
public abstract class AbstractLoadDataProcessor extends RecursiveAction implements ILoadDataProcessor{

    protected  Context context;

    @Override
    protected void compute() {
        load(context); // Call the concrete implementation of the subclass 
    }

    public Context getContext() {
        this.join(); // Get an aggregated result 
        return context;
    }

    public void setContext(Context context) {
        this.context = context;
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Item;
import org.springframework.stereotype.Service;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@Service
public class ItemService extends AbstractLoadDataProcessor{
    @Override
    public void load(Context context) {
        Item item=new Item();
        item.setNum(100);
        item.setProductName(" keyboard ");
        context.setItem(item);
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Comment;
import org.springframework.stereotype.Service;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@Service
public class CommentService extends AbstractLoadDataProcessor{
    @Override
    public void load(Context context) {
        //RPC.
        Comment comment=new Comment();
        comment.setName("Mic");
        comment.setContent(" The quality of the goods is very good ");
        context.setComment(comment);
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Seller;
import org.springframework.stereotype.Service;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@Service
public class SellerService extends AbstractLoadDataProcessor{

    @Override
   public void load(Context context) {
        Seller seller=new Seller();
        seller.setSellerNum(100);
        seller.setTotalNum(1000);
        context.setSeller(seller);
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Shop;
import org.springframework.stereotype.Service;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@Service
public class ShopService extends AbstractLoadDataProcessor{
    @Override
    public void load(Context context) {
        Shop shop=new Shop();
        shop.setName(" Gupao shop ");
        context.setShop(shop);
    }
}

 Aggregate task 
package com.example.springbootforkjoin;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinTask;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@Service
public class ComplexTradeTaskService extends AbstractLoadDataProcessor implements ApplicationContextAware {

    ApplicationContext applicationContext;

    private List<AbstractLoadDataProcessor> taskDataProcessors=new ArrayList<>();

    @Override
    public void load(Context context) {
        taskDataProcessors.forEach(abstractLoadDataProcessor->{
            abstractLoadDataProcessor.setContext(this.context);
            abstractLoadDataProcessor.fork();// Create a fork task
        });
    }

    @Override
    public Context getContext() {
        this.taskDataProcessors.forEach(ForkJoinTask::join);
        return super.getContext();
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext=applicationContext;
        taskDataProcessors.add(applicationContext.getBean(SellerService.class));
        taskDataProcessors.add(applicationContext.getBean(ShopService.class));
    }
}


package com.example.springbootforkjoin;

import com.example.springbootforkjoin.pojo.Item;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinTask;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 *
 *  Represents an aggregate task 
 **/
@Service
public class ItemTaskForkJoinDataProcessor extends AbstractLoadDataProcessor implements ApplicationContextAware {

    ApplicationContext applicationContext;

    private List<AbstractLoadDataProcessor> taskDataProcessors=new ArrayList<>();

    @Override
    public void load(Context context) {
        taskDataProcessors.forEach(abstractLoadDataProcessor->{
            abstractLoadDataProcessor.setContext(this.context);
            abstractLoadDataProcessor.fork();// Create a fork task
        });
    }
    @Override
    public Context getContext() {
        //ForkJoinTask::join  java8 Method reference 
        // *  Construct references 
        // *  Static method reference 
        // *  Instance method reference 
        this.taskDataProcessors.forEach(ForkJoinTask::join);
        return super.getContext();
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext=applicationContext;
        taskDataProcessors.add(applicationContext.getBean(CommentService.class));
        taskDataProcessors.add(applicationContext.getBean(ItemService.class));
        taskDataProcessors.add(applicationContext.getBean(ComplexTradeTaskService.class));
    }
}

Test class ：

package com.example.springbootforkjoin;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;

/**
 *  Gupao College , Just for better you 
 *  Gupao College -Mic: 2082233439
 * http://www.gupaoedu.com
 **/
@RestController
public class IndexController {

    @Autowired
    ItemTaskForkJoinDataProcessor itemTaskForkJoinDataProcessor;

    @GetMapping("/say")
    public Context index(){
        Context context=new Context();
        itemTaskForkJoinDataProcessor.setContext(context);
        ForkJoinPool forkJoinPool=new ForkJoinPool();
        forkJoinPool.submit(itemTaskForkJoinDataProcessor);
        return itemTaskForkJoinDataProcessor.getContext();
    }
}

3、 ... and 、 The demonstration effect is as shown in the figure ：

  Four 、 By taking a big task , Split into several small tasks , And then through fork Split ,join Aggregate , Form a completion context object , Include comments 、 Commodity information 、 Store information 、 Sales information . This code structure uses the template design pattern .

5、 ... and 、ForkJoinTask Use... When not shown ForkJoinPool.execute/invoke/submit() When the method is executed , You can also use your own fork/invoke Method to execute .