some other kind of synchronization and/or exclusion that allows one to exclude access to fullName while the dependent properties are being updated. To address this, you need a transactional model. In the meantime, thread B may call fullName in between thread A's two calls and will receive the new first name coupled with the old last name. In this case, thread A could be renaming the object by calling setFirstName: and then calling setLastName. Likewise, the object may end up with the value from B or C, no way to tell.Įnsuring data integrity - one of the primary challenges of multi-threaded programming - is achieved by other means.Ītomicity of a single property also cannot guarantee thread safety when multiple dependent properties are in play.Ĭonsider: copy) NSString copy) NSString atomic, copy) NSString *fullName If thread A is calling the getter simultaneously with thread B and C calling the setter with different values, thread A may get any one of the three values returned - the one prior to any setters being called or either of the values passed into the setters in B and C. What "atomic" does not do is make any guarantees about thread safety. To view downloads, simply sign in with your Apple ID. View on the Mac App Store Additional downloads Get command line tools, older versions of Xcode and beta version of other software. Thus, nonatomic is considerably faster than "atomic". Download the beta Xcode 15 This version supports the SDKs for iOS 17, iPadOS 17, macOS Sonoma, tvOS 17, and watchOS 10. In nonatomic, no such guarantees are made. That is, if thread A is in the middle of the getter while thread B calls the setter, an actual viable value - an autoreleased object, most likely - will be returned to the caller in A. As far as I know, Xcode 3.1.4 is the most recent version of Xcode for OS X 10.5. With "atomic", the synthesized setter/getter will ensure that a whole value is always returned from the getter or set by the setter, regardless of setter activity on any other thread. Xcode 3.2.x is documented as only being for OS X 10.6.x (Snow Leopard). This ensures the execution environment is kept stable. Xcode 14 requires a Mac running macOS Monterey 12.5 or later. The Xcode 14 release supports on-device debugging in iOS 11 and later, tvOS 11 and later, and watchOS 4 and later. When a new major version of macOS is released, CircleCI will update once the new major version of Xcode reaches the xx.2 release. Xcode 14 includes Swift 5.7 and SDKs for iOS 16, iPadOS 16, tvOS 16, watchOS 9, and macOS Monterey 12.3. There is also no need to declare instance variables they will be synthesized automatically, too, and will have an _ prepended to their name to prevent accidental direct access). Periodically, CircleCI will update the version of macOS each image includes to ensure the execution environment is as up to date as possible. (Note: is now the default behavior in recent versions of LLVM. If you are writing your own setter/getters, atomic/nonatomic/retain/assign/copy are merely advisory. The last two are identical "atomic" is the default behavior ( note that it is not actually a keyword it is specified only by the absence of nonatomic - atomic was added as a keyword in recent versions of llvm/clang).Īssuming that you are the method implementations, atomic vs.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |