有必要同步线程安全单例的方法(Is necessary synchronize thread safe singleton's methods)

 假设我有一个单身人士： 
 
public class MySinglton {

    private static volatile MySinglton s;
    private int x; 

    public static MySinglton getInstance() {
        if (s != null) return s;
        synchronized (MySinglton.class) {
            if (s == null) {
                s = new MySinglton();
            }
        }
        return s;
    }

    public void setX(int x){
        this.x = x;
    }

} 
 
 好的，方法getInstance是线程安全的。 我的问题是。 是否有必要修改方法setX，或者它是线程安全的，因为getInsatnce方法是线程安全的。 如果不是更好。 
 
    synchronized public void setX(int x){
        this.x = x;
    }

    public void setX(int x){
        synchronized (this) {
            this.x = x;
        }
    }
 
 或最后 
 
    ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void setX(int x){
        readWriteLock.readLock().lock();
        this.x = x;
        readWriteLock.readLock().unlock();
    }

Let say that I have a singleton: 
 
public class MySinglton {

    private static volatile MySinglton s;
    private int x; 

    public static MySinglton getInstance() {
        if (s != null) return s;
        synchronized (MySinglton.class) {
            if (s == null) {
                s = new MySinglton();
            }
        }
        return s;
    }

    public void setX(int x){
        this.x = x;
    }

} 
 
Ok, method getInstance is thread safe. My question is. Is it necessary to modify method setX, or it is thread safe because getInsatnce method is thread safe. If it is not what is better. 
 
    synchronized public void setX(int x){
        this.x = x;
    }

    public void setX(int x){
        synchronized (this) {
            this.x = x;
        }
    }
 
or finally
 
    ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void setX(int x){
        readWriteLock.readLock().lock();
        this.x = x;
        readWriteLock.readLock().unlock();
    }

原文：https://stackoverflow.com/questions/28928886