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最新推荐文章于 2024-04-07 20:29:40 发布

原创最新推荐文章于 2024-04-07 20:29:40 发布 · 1.4k 阅读

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#pair #class #string

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本文通过一个具体的并发编程案例，展示了如何使用不同的同步机制来管理共享资源的更新操作，并对比了两种方法的效果。通过模拟多个线程对共享Pair对象的x和y属性进行递增操作，探究了同步与非同步方式下数据一致性的问题。

package concurrency.lock;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

class Pair
{
    private int x , y;
    public Pair(int x, int y)
    {
        this.x = x;
        this.y = y;
    }
    
    public Pair()
    {
        this(0,0);
    }
    public int getX(){ return x;};
    public int getY(){ return y;};
    public void incrementsX(){ x++; }
    public void incrementsY(){ y++; }
    
    @Override
    public String toString()
    {
        return "x: " + x + ", y: " + y;
    }
    
    public class PairValuesNotEqualException extends RuntimeException
    {
//        private static final long serialVersionUID = 1720136381044242317L;

        public PairValuesNotEqualException()
        {
            super("Pair values not equal: " + Pair.this);
        }
    }
    public void checkState()
    {
        if(x != y)
        {
            throw new PairValuesNotEqualException();
        }
    }
}

abstract class PairManager
{
    AtomicInteger checkCounter = new AtomicInteger(0);
    protected Pair p = new Pair();
    private  List<Pair> storage = Collections.synchronizedList(new ArrayList<Pair>());
    
    public synchronized Pair getPair()
    {
        return new Pair(p.getX(),p.getY());
    }
    
    protected void store(Pair p)
    {
        storage.add(p);
        try
        {
            TimeUnit.MILLISECONDS.sleep(50);
        }catch(InterruptedException igonre){}
    }
    
    public abstract void increment();
}

class PairManager1 extends PairManager
{
    @Override
    public synchronized void increment()
    {
        p.incrementsX();
        p.incrementsY();
        store(getPair());
    }
}

class PairManager2 extends PairManager
{
    public void increment()
    {
        Pair temp;
        synchronized(this)
        {
            p.incrementsX();
            p.incrementsY();
            temp = getPair();
        }
        store(temp);
    }
}

class PairManipulator implements Runnable
{
    private PairManager pm;
    public PairManipulator(PairManager pm)
    {
        this.pm = pm;
    }
    public void run()
    {
        while(true)
        {
            pm.increment();
        }
    }
    
    @Override
    public String toString()
    {
        return "Pair: " + pm.getPair() + 
        " checkCounter = " + pm.checkCounter.get();
    }
    
}

class PairChecker implements Runnable
{
    private PairManager pm;
    public PairChecker(PairManager pm)
    {
        this.pm = pm; 
    }
    public void run()
    {
        while(true)
        {
            pm.checkCounter.incrementAndGet();
            pm.getPair().checkState();
        }
    }
}


public class CriticalSection
{
    static void testApproaches(PairManager pmna1,PairManager pmna2)
    {
        ExecutorService exec = Executors.newCachedThreadPool();
        PairManipulator
            pm1 = new PairManipulator(pmna1),
            pm2 = new PairManipulator(pmna2);
        
        PairChecker
            pcheck1 = new PairChecker(pmna1),
            pcheck2 = new PairChecker(pmna2);
        
        exec.execute(pm1);
        exec.execute(pm2);
        exec.execute(pcheck1);
        exec.execute(pcheck2);
        
        try
        {
            TimeUnit.MILLISECONDS.sleep(500);
        }catch(InterruptedException e)
        {
            System.out.println("Sleep interrupted");
        }
        System.out.println("pm1 : " + pm1 + "\npm2: " + pm2);
        System.exit(0);
    }
    
    public static void main(String args[])
    {
        PairManager 
            pman1 = new PairManager1(),
            pman2 = new PairManager2();
        testApproaches(pman1, pman2);
    }
}