What is nonatomic ?

Hi Sachin,

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.)

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

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.

Reference:
Apple Docs

Thanks

1 Reply

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Chintan Rathod13y ago
Hi Sachin,

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.)

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

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.

Reference:
Apple Docs

Thanks