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Core Foundation

Core Foundation is sufficiently thread-safe that, if you program with care, you should not run into any problems related to competing threads. It is thread-safe in the common cases, such as when you query, retain, release, and pass around immutable objects. Even central shared objects that might be queried from more than one thread are reliably thread-safe.

Like Cocoa, Core Foundation is not thread-safe when it comes to mutations to objects or their contents. For example, modifying a mutable data or mutable array object is not thread-safe, as you might expect, but neither is modifying an object inside of an immutable array. One reason for this is performance, which is critical in these situations. Moreover, it is usually not possible to achieve absolute thread safety at this level. You cannot rule out, for example, indeterminate behavior resulting from retaining an object obtained from a collection. The collection itself might be freed before the call to retain the contained object is made.

In those cases where Core Foundation objects are to be accessed from multiple threads and mutated, your code should protect against simultaneous access by using locks at the access points. For instance, the code that enumerates the objects of a Core Foundation array should use the appropriate locking calls around the enumerating block to protect against someone else mutating the array.

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