属性“非原子”是什么，意思？ [英] What does the property "Nonatomic" mean?

问题描述

这段代码中的非原子是什么意思？

What does "nonatomic" mean in this code?

@property(nonatomic, retain) UITextField *theUsersName;

原子和非原子之间有什么区别？

What is the difference between atomic and nonatomic?

感谢

推荐答案

查看 Apple文档。

基本上，如果您说非原子，并使用 @synthesize 生成访问器，然后如果多个线程尝试更改/读取属性一旦，坏会发生。您可以获取部分写入的值或过度释放/保留的对象，这很容易导致崩溃。 （这可能比原子访问器快很多。）

Basically, if you say nonatomic, and you generate the accessors using @synthesize, then if multiple threads try to change/read the property at once, badness can happen. You can get partially-written values or over-released/retained objects, which can easily lead to crashes. (This is potentially a lot faster than an atomic accessor, though.)

如果使用默认值（ atomic ;以前没有关键字，但有现在是），那么 @synthesize d方法使用对象级锁来确保对单个属性的多次读取/写入被序列化。正如苹果文档指出，这并不意味着整个对象是线程安全的，但是单个属性的读/写是。

If you use the default (which is atomic; there used to be no keyword for this, but there is now), then the @synthesized methods use an object-level lock to ensure that multiple reads/writes to a single property are serialized. As the Apple docs point out, this doesn't mean the whole object is thread-safe, but the individual property reads/writes are.

当然，如果你实现你自己的访问器而不是使用 @synthesize ，我认为这些声明什么都不做，除了表达你的意图是否属性是以线程安全的方式实现。

Of course, if you implement your own accessors rather than using @synthesize, I think these declarations do nothing except express your intent as to whether the property is implemented in a threadsafe manner.

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