[WIP] Raw storage and locks/atomics prototype #67425
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@swift-ci Please test |
This attribute can be attached to a noncopyable struct to specify that its storage is raw, meaning the type definition is (with some limitations) able to do as it pleases with the storage. This provides a basis for implementing types for things like atomics, locks, and data structures that use inline storage to store conditionally-initialized values. The example in `test/Prototypes/UnfairLock.swift` demonstrates the use of a raw layout type to wrap Darwin's `os_unfair_lock` APIs, allowing a lock value to be stored inside of classes or other types without needing a separate allocation, and using the borrow model to enforce safe access to lock-guarded storage.
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Strawman implementation of a
@_rawLayoutattribute that gives a noncopyable struct a layout consisting of inline raw memory it can mostly do as it pleases with. As a proof of concept, show how this can be used to implement a safe wrapper overos_unfair_lockthat can be stored inline within a class or other move-only type without an additional allocation.