Java同步差异线程

Question

这个问题已经有答案了:

已关闭 11 年前。

Possible Duplicate:
What is the difference between a synchronized method and synchronized block in Java?
What is the difference between a synchronized function and synchronized block?

我不明白这两个线程代码之间的区别，我相信这是为了互斥，但我不明白有什么区别，你能帮助我吗？

public synchronized void Method1 () {
  }

public myFunction (){
       synchronized (this) { 
     }
 }

感谢您的帮助。

Answer 1

唯一的区别是减少了由锁保护的操作数量，这可以大大提高性能。

示例:假设我们有一个 servlet，它在输入中给出一系列大数字的因子，并且我们想要计算 servlet 的启动频率。问题在于同步对状态变量 requestsCount

的访问

//Poor performance
class PoorFactorizer implements Servlet {
    private int requestsCount = 0;
    public synchronized void service(ServletRequest req, ServletResponse res) {
        BigInteger numberToFactorize = extractFromRequest(req);
        BigInteger[] factors = factorize(numberToFactorize); // long lasting
                                 // operation makes everyone wait 
        requestCount++;
        encodeResponse(res, factors);
    }
}

//Better perfomance
class PoorFactorizer implements Servlet {
    private int requestsCount = 0;
    public void service(ServletRequest req, ServletResponse res) {
        BigInteger numberToFactorize = extractFromRequest(req);
        BigInteger[] factors = factorize(numberToFactorize); 
        // since we need to guard only the class' state
        // let's guard only the operation with the state
        synchronized(this) {            
            requestCount++;
        }
        encodeResponse(res, factors);
    }
}  

UPD:你可以在一本杰作《Java并发实践》(第2章)中读到非常好的解释。我强烈建议您从头到尾阅读这本书。