java - 消费品生产商

Question

ProdCom.java(驱动程序类)

import static java.lang.System.out;


public class ProdCom{
    static int full = 50;
    static int mutx = 0;
    static int empty = 0;
    static int currentSize = 0;
   
    public static void acquire(){
        while (mutx == 1);
        
        mutx++;
        
    }
    
    public static void release(){
        mutx--;
    }
    
 
    public static void main(String args[]){
        Thread t = new Thread(new Producerr());
        Thread t1 = new Thread(new Consumerr());
                
        t.start();
        t1.start();
    }
   
    
}

Producerr.java

class Producerr implements Runnable{
        
        
        public void wwait(){
            while (ProdCom.currentSize >= ProdCom.full){
                
            } 
            
        } public void signal(){
            ProdCom.currentSize++;
        }
        
        public void run(){
            do{
                this.wwait();
                
                ProdCom.acquire();
                
                out.println("Num elements" + ProdCom.currentSize);
                out.println("producing!");
                
                ProdCom.release();
                this.signal();
            } while (true);
        }
    }

Consumerr.java

class Consumerr implements Runnable{
        public void wwait(){
            while (ProdCom.currentSize <= 0){
                out.println("inside consumer wait: ");
                out.println("number of elements: " + ProdCom.currentSize);
            } 
            
        } public void signal(){
            ProdCom.currentSize--;
            
        }
        
      
        public void run(){
            do{
               
                this.wwait();
                ProdCom.acquire();
               
                out.println("Num elements" + ProdCom.currentSize);
                out.println("Consuming!");
                
                ProdCom.release();
                this.signal();
            } while (true);
        } 
    }
           

以上是我对消费者生产者问题的解决方案。驱动程序类 ProdCom具有变量 full， empty和 mutx，用于控制生产者 t和消费者 t1对变量 currentSize的访问(从而模拟缓冲区中的当前项目数)。但是当我运行代码时，输​​出似乎表明t1和t并没有轮流更改 currentSize，而是其中之一永远重复并卡住了……我想知道为什么吗？谢谢。

Answer 1

我对您的代码进行了一些改进，您会注意到Joni提到的许多概念都已考虑在内。
ProdCom.java

import java.lang.*;

public class ProdCom{
    static final int FULL = 50;
    static final int EMPTY = 0;

    static volatile int mutx = 0;
    static volatile int currentSize = 0;
    static Object lockObject = new Object();
   
    public static void acquire(){
        /* since mutx is defined volatile, the spinlock works,
           but you reconsider this approach. There are cheaper
           methods of heating the room */
        while (mutx == 1);
        
        mutx++;
        
    }

    public static boolean isEmpty() {
        synchronized(lockObject) {
            if (currentSize <= EMPTY) return true;
            return false;
        }
    }
    
    public static boolean isFull() {
        synchronized(lockObject) {
            if (currentSize >= FULL) return true;
            return false;
        }
    }

    public static int getCurrentSize() {
        synchronized(lockObject) {
            return currentSize;
        }
    }
    
    public static void release(){
        mutx--;
    }

    public static void incCurrentSize()
    {
        synchronized(lockObject) {
            currentSize++;
        }
    }
    
    public static void decCurrentSize()
    {
        synchronized(lockObject) {
            currentSize--;
        }
    }
    
 
    public static void main(String args[]){
        Thread t = new Thread(new Producerr());
        Thread t1 = new Thread(new Consumerr());
                
        t.start();
        t1.start();
    }
   
    
}

Consumerr.java

import java.lang.*;

class Consumerr implements Runnable {

    public void wwait() {
        while (ProdCom.isEmpty()){
            System.out.println("inside consumer wait: ");
            System.out.println("number of elements: " + ProdCom.getCurrentSize());
            try {
                /* we don't spinlock here */
                Thread.sleep(50);
            } catch (Exception e) {
                /* do nothing */
            }
        } 
        
    }

    public void signal(){
        ProdCom.decCurrentSize();
        
    }
    
      
    public void run(){
        do{
            this.wwait();
            ProdCom.acquire();
               
            System.out.println("Num elements " + ProdCom.getCurrentSize());
            System.out.println("Consuming!");
            this.signal();
            
            ProdCom.release();
        } while (true);
    } 
}

Producerr.java

import java.lang.*;

class Producerr implements Runnable {

    public void wwait(){
        while (ProdCom.isFull()){
            try {
                Thread.sleep(50);
            } catch(Exception e) { /* do nothing */ }
        } 

    }
    public void signal(){
        ProdCom.incCurrentSize();
    }

    public void run(){
        do {
            this.wwait();

            ProdCom.acquire();

            System.out.println("Num elements : " + ProdCom.getCurrentSize());
            System.out.println("producing!");
            this.signal();

            ProdCom.release();
        } while (true);
    }
}