多线程 - java 线程同步问题

Question

如下两个线程类：

public class A implements Runnable{
    private StringBuilder sb;
    
    @Override
    public void run() {
        //操作sb缓冲
        .......
    }
    public StringBuilder getsb() {
        return sb;
    }

    public void setsb(StringBuilder sb) {
        this.sb = sb;
    }
}

public class B implements Runnable{
    //此处得到A类的对象a
    
    @Override
    public void run() {
        //操作a.getsb()缓冲
        .......
    }
}

如何能保证，A、B互斥？

A的线程在操作sb的时候加锁，让B不能操作；或者B的线程在操作sb的时候加锁，让A不能操作

始终只有一个线程可以操作sb！！

Answer 1

public class A implements Runnable{
    private StringBuilder sb;
    
    @Override
    public void run() {
        //操作sb缓冲
        
        synchronized(sb){
        
        }
        .......
    }
    public StringBuilder getsb() {
        return sb;
    }

    public void setsb(StringBuilder sb) {
        this.sb = sb;
    }
}

public class B implements Runnable{
    //此处得到A类的对象a
    
    @Override
    public void run() {
        //操作a.getsb()缓冲
        synchronized(a.getsb()){
        
        }
        
        .......
    }
}

Answer 2

Try itsynchronized, it has several granularities.
It can be added to the code block like @scort, or it can be added to the object.

Answer 3

synchronized or ReentrantLock. Someone gave an example of synchronized before. I will give an example of ReentrantLock here:

ReentrantLock lock = new ReentrantLock(); 
lock.lock();  
try {  
    // 这里是对sb的操作  
} finally {  
    lock.unlock();  
} 

Answer 4

At this time, you can consider using StringBuffer directly. The only difference from StringBuilder is that the former is thread-safe.

Answer 5

I personally think you should put forward the method that requires thread execution first, then add a lock to the method, and then remove multiple threads and it should be possible