objective-c - cocoa 非原子特性

Question

当您查看一些 Objective-C 代码时，您经常会看到定义为非原子的类属性。为什么？当您不使用线程时，它是否会给您带来一些性能提升，或者还有其他原因吗？

Answer 1

非原子访问器速度更快，因为它们不必锁定。这就是全部内容了。来自 documentation :

If you do not specify nonatomic, then in a reference counted environment a synthesized get accessor for an object property uses a lock and retains and autoreleases the returned value—the implementation will be similar to the following:

[_internal lock]; // lock using an object-level lock
id result = [[value retain] autorelease];
[_internal unlock];
return result;

If you specify nonatomic, then a synthesized accessor for an object property simply returns the value directly.