Multithreading (threaded Communication [producer and consumer])

1 Producer consumer

   Threads are not independent of each other , They need to communicate and collaborate with each other , The most typical example is the producer - Consumer issues .

   Suppose there is only one product in the warehouse , The products produced by the producer are put into the warehouse , Consumers take products from the warehouse .

   If there is no product in the warehouse , Then the producer puts the product in the warehouse , Otherwise stop production and wait , Until the products in the warehouse are taken away by consumers .

   If there are products in the warehouse , Then the consumer takes the product away , Otherwise, stop consumption and wait .

   The process of communicating with each other is Thread collaboration .

2 wait/notify Realization

   Thread communication can be through wait and notify or notifyAll To implement .

• wait() ： Let the current thread release the object lock and enter the wait （ Blocking ） state .
• notify()： Wake up a thread waiting for the corresponding object lock , Put it in the ready queue , In order to compete for the lock after the current thread releases the lock , And then you get CPU Implementation .
• notifyAll()： Wake up all threads waiting for the corresponding object lock , Put them in the ready queue , In order to compete for the lock after the current thread releases the lock , And then you get CPU Implementation .

   First of all, we should sort out what we need ： producer 、 product 、 consumer 、 Warehouse .

2.1 producer

public class Producer extends Thread {
    

    Warehouse warehouse;	//  Warehouse 

    public Producer(Warehouse warehouse) {
    
        this.warehouse = warehouse;
    }

    @Override
    public void run() {
    
        //  Produce products and put them in the warehouse 
        for(int i = 0; i < 100; i++) {
    
            warehouse.push(new Product(i));
            System.out.println(" Produced " + (i + 1) + " Product No ");
        }
    }
}

2.2 product

/** *  product  */
public class Product {
    

    private Integer id; //  goods  id

    public Product(Integer id) {
    
        this.id = id;
    }

    /** *  Get product  ID * @return */
    public Integer getId() {
    
        return this.id;
    }
}

2.3 consumer

public class Consumer extends Thread {
    

    Warehouse warehouse;	//  Warehouse 

    public Consumer(Warehouse warehouse) {
    
        this.warehouse = warehouse;
    }

    @Override
    public void run() {
    
        //  Consumer products 
        for(int i = 0; i < 100; i++) {
    
            Product product = warehouse.pop();
            System.out.println(" The consumption " + product.getId()+ " Product No ");
        }
    }
}

2.4 Warehouse

/** *  Warehouse  */
public class Warehouse {
    

    private Product[] products = new Product[10]; //  Commodity queue 
    private int count = 0;  //  Queue counter 

    /** *  Put the product  * @param product */
    public synchronized void push(Product product) {
    
        //  If the line of goods is full , Need to wait for consumers to spend 
        if(count == 10) {
    
            try {
    
                this.wait();
            }
            catch (Exception e) {
    
                e.printStackTrace();
            }
        }
        //  If it's not full , Put it in the queue 
        products[count] = product;
        count++;
        //  Inform consumers of consumption 
        this.notifyAll();
    }

    /** *  Consumer products  */
    public synchronized Product pop() {
    
        //  If the product queue is gone , Need to wait for the producer to produce 
        if(count == 0) {
    
            try {
    
                this.wait();
            }
            catch (Exception e) {
    
                e.printStackTrace();
            }
        }
        count--;
        Product product = products[count];
        //  Inform the producer to produce 
        this.notifyAll();
        return product;
    }
}

2.5 test

public class MainTest {
    

    public static void main(String[] args) throws Exception {
    
        Warehouse warehouse = new Warehouse();  //  Create repository 
        new Producer(warehouse).start(); //  Create the producer thread and start it 
        new Consumer(warehouse).start(); //  Create and launch the consumer thread 
    }
}

Console output

	 Produced 1 Product No 
	 Produced 2 Product No 
	 Produced 3 Product No 
	 Produced 4 Product No 
	 Produced 5 Product No 
	 Produced 6 Product No 
	 Produced 7 Product No 
	 Produced 8 Product No 
	 Produced 9 Product No 
	 Produced 10 Product No 
	 The consumption 9 Product No 
	 The consumption 8 Product No 
	 The consumption 7 Product No 
	 The consumption 6 Product No 
	 The consumption 5 Product No 
	 Produced 11 Product No 

It can be seen that , Sir gave birth 10 Products , Start consuming when the queue is full , When the queue is not full, start production again .