问题描述
据说非原子选项会让您的 setter方法运行得更快。我用谷歌搜索，但我无法理解。有人可以告诉我为什么吗？
It is said that nonatomic option will make your setter method run faster. I googled it but am not able to understand. Could someone tell me why?
推荐答案
声明属性 atomic 使编译器成为可能生成阻止并发访问该属性的其他代码。此附加代码锁定信号量，然后获取或设置属性，然后解锁信号量。与设置或获取原始值或指针相比，锁定和解锁信号量是昂贵的（尽管如果考虑应用程序的总体流量，通常可以忽略不计）。
Declaring a property atomic makes compiler generate additional code that prevents concurrent access to the property. This additional code locks a semaphore, then gets or sets the property, and then unlock the semaphore. Compared to setting or getting a primitive value or a pointer, locking and unlocking a semaphore is expensive (although it is usually negligible if you consider the overall flow of your app).
由于iOS下的大多数类，特别是与UI相关的类，将在单线程环境中使用，因此可以安全地删除 atomic （即写入 nonatomic ，因为默认情况下属性是 atomic ：即使操作相对便宜，你也不想支付费用你不需要的。
Since most of your classes under iOS, especially the ones related to UI, will be used in a single-threaded environment, it is safe to drop atomic (i.e. write nonatomic, because properties are atomic by default): even though the operation is relatively inexpensive, you do not want to pay for things that you do not need.
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