如果我没有同步这个方法，我会得到错误的值？

Question

public static int getCRC16(byte[] bytes) {
    CRC16 crc = new CRC16();
    crc.reset();
    crc.update(bytes, 0, bytes.length);
    return (int) crc.getValue();
}

Tons of threads will hit this method, if I don't synchronize I'll get a wrong crc for a specific thread?

Answer 1

No, it is fine, as long as you don't use any shared variables. The bytes and crc are local per thread. That's why they are called local variables.

Answer 2

This is a static method. Usually you need to worry about thread safety when you're dealing with the state of an object. For example, if you were changing values inside the CRC16 class itself, but you're not. Your function just takes an input bytes and returns an output crc.getValue() .

Answer 3

扩展其他答案，线程不扩展关于可见性和范围的Java语言，仅关于代码的执行模式，这意味着只需要一个对象可以访问的值或者只在本地有效的值不需要同步 - 仅如果在多个对象之间共享值（类的静态字段，或者所有访问者返回相同对象的单例实例），则同步值得哲学化。