Swift's dynamic exclusivity checking relies on two functions,
_swift_getExclusivityTLS and _swift_setExclusivityTLS, to properly
deal with multi-threaded contexts. In the non-Embedded standard
library, these are provided by the Swift runtime.
For Embedded Swift, we cannot rely on having thread-local storage.
Instead, require the platform to provide these two entrypoints. To
make things simpler, we offer two implementations one can link in:
- libswiftExclusivitySingleThreaded.a: single-threaded implementation
- libswiftExclusivityC11ThreadLocal.a: multi-threaded implementation that
uses C11 thread-locals
Embedded Swift programs using dynamic exclusivity can link in one of
these libraries, or can implement its own versions of these two
functions. A platform can choose to provide them if it has different
mechanisms for thread-local storage.
This makes dynamic exclusivity checking generally usable in Embedded
Swift, rdar://159115910.
