Threading Support API¶
Libc++ supports using multiple different threading models and configurations
to implement the threading parts of libc++, including
These different models provide entirely different interfaces from each
other. To address this libc++ wraps the underlying threading API in a new and
consistent API, which it uses internally to implement threading primitives.
<__thread/support.h> header is where libc++ defines its internal
threading interface. It documents the functions and declarations required
to fullfil the internal threading interface.
In order to support vendors with custom threading API’s libc++ allows the entire internal threading interface to be provided by an external, vendor provided, header.
_LIBCPP_HAS_THREAD_API_EXTERNAL is defined the
header simply forwards to the
<__external_threading> header (which must exist).
It is expected that the
<__external_threading> header provide the exact
interface normally provided by
libc++ can be compiled with its internal threading API delegating to an external library. Such a configuration is useful for library vendors who wish to distribute a thread-agnostic libc++ library, where the users of the library are expected to provide the implementation of the libc++ internal threading API.
On a production setting, this would be achieved through a custom
<__external_threading> header, which declares the libc++ internal threading
API but leaves out the implementation.
This macro is defined when libc++ is built without threading support. It should not be manually defined by the user.
This macro is defined when libc++ should use the
<__external_threading>header to provide the internal threading API. This macro overrides
This macro is defined when libc++ should use POSIX threads to implement the internal threading API.
This macro is defined when libc++ should use C11 threads to implement the internal threading API.
This macro is defined when libc++ should use Win32 threads to implement the internal threading API.