mirror of
https://github.com/capstone-engine/llvm-capstone.git
synced 2025-02-04 00:06:50 +00:00
8c2bf45da9
This patch further decouples libc++ from pthread, allowing libc++ to be built against other threading systems. There are two main use cases: - Building libc++ against a thread library other than pthreads. - Building libc++ with an "external" thread API, allowing a separate library to provide the implementation of that API. The two use cases are quite similar, the second one being sligtly more de-coupled than the first. The cmake option LIBCXX_HAS_EXTERNAL_THREAD_API enables both kinds of builds. One needs to place an <__external_threading> header file containing an implementation of the "libc++ thread API" declared in the <__threading_support> header. For the second use case, the implementation of the libc++ thread API can delegate to a custom "external" thread API where the implementation of this external API is provided in a seperate library. This mechanism allows toolchain vendors to distribute a build of libc++ with a custom thread-porting-layer API (which is the "external" API above), platform vendors (recipients of the toolchain/libc++) are then required to provide their implementation of this API to be linked with (end-user) C++ programs. Note that the second use case still requires establishing the basic types that get passed between the external thread library and the libc++ library (e.g. __libcpp_mutex_t). These cannot be opaque pointer types (libc++ sources won't compile otherwise). It should also be noted that the second use case can have a slight performance penalty; as all the thread constructs need to cross a library boundary through an additional function call. When the header <__external_threading> is omitted, libc++ is built with the "libc++ thread API" (declared in <__threading_support>) as the "external" thread API (basic types are pthread based). An implementation (pthread based) of this API is provided in test/support/external_threads.cpp, which is built into a separate DSO and linked in when running the libc++ test suite. A test run therefore demonstrates the second use case (less the intermediate custom API). Differential revision: https://reviews.llvm.org/D21968 Reviewers: bcraig, compnerd, EricWF, mclow.lists llvm-svn: 281179