[cmake] Add a config option LIBCXX_HAS_WIN32_THREAD_API for enforcing win32 threads

This allows keeping libcxx using win32 threads even if a
version of pthread.h is installed.

This matches the existing cmake option LIBCXX_HAS_PTHREAD_API.

Also add missing documentation about the internal define
_LIBCPP_HAS_THREAD_API_WIN32.

Differential Revision: https://reviews.llvm.org/D41764

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@321896 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -202,6 +202,7 @@ option(LIBCXX_ENABLE_MONOTONIC_CLOCK
    This option may only be set to OFF when LIBCXX_ENABLE_THREADS=OFF." ON)
 option(LIBCXX_HAS_MUSL_LIBC "Build libc++ with support for the Musl C library" OFF)
 option(LIBCXX_HAS_PTHREAD_API "Ignore auto-detection and force use of pthread API" OFF)
+option(LIBCXX_HAS_WIN32_THREAD_API "Ignore auto-detection and force use of win32 thread API" OFF)
 option(LIBCXX_HAS_EXTERNAL_THREAD_API
   "Build libc++ with an externalized threading API.
    This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON." OFF)
@@ -273,6 +274,10 @@ if(NOT LIBCXX_ENABLE_THREADS)
     message(FATAL_ERROR "LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY can only be set "
                         "to ON when LIBCXX_ENABLE_THREADS is also set to ON.")
   endif()
+  if (LIBCXX_HAS_WIN32_THREAD_API)
+    message(FATAL_ERROR "LIBCXX_HAS_WIN32_THREAD_API can only be set to ON"
+                        " when LIBCXX_ENABLE_THREADS is also set to ON.")
+  endif()
 
 endif()
 
@@ -287,6 +292,19 @@ if (LIBCXX_HAS_EXTERNAL_THREAD_API)
                         "and LIBCXX_HAS_PTHREAD_API cannot be both"
                         "set to ON at the same time.")
   endif()
+  if (LIBCXX_HAS_WIN32_THREAD_API)
+    message(FATAL_ERROR "The options LIBCXX_HAS_EXTERNAL_THREAD_API"
+                        "and LIBCXX_HAS_WIN32_THREAD_API cannot be both"
+                        "set to ON at the same time.")
+  endif()
+endif()
+
+if (LIBCXX_HAS_PTHREAD_API)
+  if (LIBCXX_HAS_WIN32_THREAD_API)
+    message(FATAL_ERROR "The options LIBCXX_HAS_PTHREAD_API"
+                        "and LIBCXX_HAS_WIN32_THREAD_API cannot be both"
+                        "set to ON at the same time.")
+  endif()
 endif()
 
 # Ensure LLVM_USE_SANITIZER is not specified when LIBCXX_GENERATE_COVERAGE
@@ -613,6 +631,7 @@ config_define_if_not(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS _LIBCPP_HAS_NO_THRE
 
 config_define_if(LIBCXX_HAS_PTHREAD_API _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define_if(LIBCXX_HAS_EXTERNAL_THREAD_API _LIBCPP_HAS_THREAD_API_EXTERNAL)
+config_define_if(LIBCXX_HAS_WIN32_THREAD_API _LIBCPP_HAS_THREAD_API_WIN32)
 config_define_if(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
 config_define_if(LIBCXX_HAS_MUSL_LIBC _LIBCPP_HAS_MUSL_LIBC)
 config_define_if(LIBCXX_NO_VCRUNTIME _LIBCPP_NO_VCRUNTIME)

docs/DesignDocs/ThreadingSupportAPI.rst

@@ -66,6 +66,10 @@ Threading Configuration Macros
   This macro is defined when libc++ should use POSIX threads to implement the
   internal threading API.
 
+**_LIBCPP_HAS_THREAD_API_WIN32**
+  This macro is defined when libc++ should use Win32 threads to implement the
+  internal threading API.
+
 **_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL**
   This macro is defined when libc++ expects the definitions of the internal
   threading API to be provided by an external library. When defined

include/__config_site.in

@@ -23,6 +23,7 @@
 #cmakedefine _LIBCPP_HAS_MUSL_LIBC
 #cmakedefine _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine _LIBCPP_HAS_THREAD_API_EXTERNAL
+#cmakedefine _LIBCPP_HAS_THREAD_API_WIN32
 #cmakedefine _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL
 #cmakedefine _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS
 #cmakedefine _LIBCPP_NO_VCRUNTIME