dispatch: split DISPATCH_EXPORT and prepare for static linking
#872
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This change accomplishes two items: 1. splits out a new `DISPATCH_EXTERN` macro to decorate with `extern` or `extern "C"` based on the compilation mode (C vs C++). 2. enables a new configuration macro (`dispatch_STATIC`) that allows building with libdispatch for static linking. The default remains dynamic linking. The motivation for `DISPATCH_EXTERN` is primarily being able to concisely define `DISPATCH_EXPORT`. This follows the naming scheme that most other Apple frameworks use (e.g. UIKit, Foundation, etc). The change to introduce support for static linking is motivated by Windows. With the gradual roll out of static linking of the runtime, it would be convenient to be able to statically link dispatch into a fully sealed Swift program. Doing so requires building libdispatch without the `__declspec(dllexport)` and `__declspec(dllimport)` attributes on Windows. Similarly, it would be unfortunate to have dispatch's ABI be subsumed by a client library and have it participate in dynamic linking. The user is responsible for defining `dispatch_STATIC` when using a static copy of libdispatch. This allows the default to remain dynamic linking (which is the preferred style on Darwin and Windows).
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@swift-ci please test |
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This change accomplishes two items:
DISPATCH_EXTERNmacro to decorate withexternorextern "C"based on the compilation mode (C vs C++).dispatch_STATIC) that allows building with libdispatch for static linking. The default remains dynamic linking.The motivation for
DISPATCH_EXTERNis primarily being able to concisely defineDISPATCH_EXPORT. This follows the naming scheme that most other Apple frameworks use (e.g. UIKit, Foundation, etc).The change to introduce support for static linking is motivated by Windows. With the gradual roll out of static linking of the runtime, it would be convenient to be able to statically link dispatch into a fully sealed Swift program. Doing so requires building libdispatch without the
__declspec(dllexport)and__declspec(dllimport)attributes on Windows. Similarly, it would be unfortunate to have dispatch's ABI be subsumed by a client library and have it participate in dynamic linking.The user is responsible for defining
dispatch_STATICwhen using a static copy of libdispatch. This allows the default to remain dynamic linking (which is the preferred style on Darwin and Windows).