libcxx: Move Windows threading support into a .cpp file.

[pcc]

Summary

This allows us to avoid polluting the namespace of users of <thread>
with the definitions in windows.h.

[mstorsjo]

Sounds like a great idea! This would avoid e.g. this issue I've recently run into (and worked around): https://codereview.qt-project.org/216903

[smeenai]

This prevents inlining, which might not be great. I'd be happier if we kept everything in the header but just forward declared whatever we needed from the Windows headers rather than actually including them (I've been meaning to do that for a while, just haven't gotten the chance to work on it yet).

Also, IIRC, a CRITICAL_SECTION is actually a 40-byte sized struct, so replacing CRITICAL_SECTION with void * is gonna cause issues.

[pcc]

This prevents inlining, which might not be great.

It doesn't seem like a big problem to me. Many of these APIs will result in system calls, and the cost of not inlining is probably dwarfed by the cost of the system call.

Also, IIRC, a CRITICAL_SECTION is actually a 40-byte sized struct, so replacing CRITICAL_SECTION with void * is gonna cause issues.

So it is. I'll fix that.

[smeenai]

It doesn't seem like a big problem to me. Many of these APIs will result in system calls, and the cost of not inlining is probably dwarfed by the cost of the system call.

They'll only cause system calls in case of contention, right? SRWLock in particular is supposed to be super lightweight. I agree that it's probably not a huge deal in practice, but it seems like if you already have to provide some fake types to make the header happy, you might as well go all the way with your own prototypes.

[smeenai]

With that said, I'd be fine with this patch as-is (once the critical section issue is fixed); we can always restore the inlining later whenever someone gets the time/if it does turn out to be an issue. libc++ on Windows will miss out on lots of inlining opportunities because of dllimport anyway (clang doesn't inline a dllimport function if it calls a non-dllimport function, which pessimizes lots of libc++ dllimport functions which call trivial non-dllimport helpers, e.g. basic_string::data calling _VSTD::__to_raw_pointer), so there are bigger problems already.

[pcc]

• Add compatible definitions of __libcpp_recursive_mutex_t

[mstorsjo]

libcxx/include/__threading_support

87 ↗

(On Diff #130731)

|| defined(_M_ARM64) here as well - there, it has the same size (40 bytes) as on x86_64.

[mstorsjo]

libcxx/include/__threading_support

87 ↗

(On Diff #130731)

Oh, also - please add checks for corresponding GCC defines, to keep things working for clang in mingw mode. (__aarch64__ etc)

[pcc]

• Add some more defined checks

[mstorsjo]

LGTM now, but I'll let @smeenai give it the proper approval.

[smeenai]

LGTM.

libcxx/src/support/win32/thread_win32.cpp

18–39 ↗

(On Diff #130952)

Awesome.

[eastig]

Hi Peter,

We have libcxx-externally-threaded-x86 failing due to the changes:

$ cmake ../llvm -DCMAKE_BUILD_TYPE=MinSizeRel -DCMAKE_C_COMPILER=/work/clang-3.9/bin/clang -DCMAKE_CXX_COMPILER=/work/clang-3.9/bin/clang++ -DLLVM_ENABLE_ASSERTIONS=ON -DLIBCXX_ENABLE_ASSERTIONS=ON -DLIBCXXABI_USE_LLVM_UNWINDER=ON -DLLVM_LIT_ARGS=-sv -DLIBCXX_ENABLE_SHARED=OFF -DLIBCXXABI_ENABLE_SHARED=OFF -DLIBUNWIND_ENABLE_SHARED=OFF -DLIBCXXABI_ENABLE_STATIC_UNWINDER=ON -DLIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY=ON -DLIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY=ON -G Ninja
...
$ ninja -j32 cxxabi
...
/work/clang-3.9/bin/clang++   -DHAVE___CXA_THREAD_ATEXIT_IMPL -DLIBCXXABI_USE_LLVM_UNWINDER -D_DEBUG -D_GNU_SOURCE -D_LIBCPP_DISABLE_EXTERN_TEMPLATE -D_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL -D_LIBCXXABI_BUILDING_LIBRARY -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Iprojects/libcxxabi/src -I/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxxabi/src -I/usr/include/libxml2 -Iinclude -I/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/include -I/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxxabi/include -I/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libunwind/include -I/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxx/include -fPIC -fvisibility-inlines-hidden -Werror=date-time -std=c++11 -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fcolor-diagnostics -ffunction-sections -fdata-sections  -Os  -fPIC   -UNDEBUG -nostdinc++ -Werror=return-type -W -Wall -Wchar-subscripts -Wconversion -Wmismatched-tags -Wmissing-braces -Wnewline-eof -Wunused-function -Wshadow -Wshorten-64-to-32 -Wsign-compare -Wsign-conversion -Wstrict-aliasing=2 -Wstrict-overflow=4 -Wunused-parameter -Wunused-variable -Wwrite-strings -Wundef -Wno-error -pedantic -fstrict-aliasing -funwind-tables -D_DEBUG -D_LIBCPP_BUILD_STATIC -std=c++11 -MD -MT projects/libcxxabi/src/CMakeFiles/cxxabi_objects.dir/cxa_guard.cpp.o -MF projects/libcxxabi/src/CMakeFiles/cxxabi_objects.dir/cxa_guard.cpp.o.d -o projects/libcxxabi/src/CMakeFiles/cxxabi_objects.dir/cxa_guard.cpp.o -c /work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxxabi/src/cxa_guard.cpp
In file included from /work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxxabi/src/cxa_guard.cpp:13:
/work/llvm-test/slave/libcxx-externally-threaded-x86/llvm/projects/libcxx/include/__threading_support:117:35: error: unknown type name '__libcpp_recursive_mutex_t'
int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m);
...

You can see we use Clang 3.9.
Any idea how to fix it?

Thanks,
Evgeny Astigeevich

[pcc]

In D42214#986163, @eastig wrote:

Hi Peter,

We have libcxx-externally-threaded-x86 failing due to the changes:

I think this should be fixed by D42503.

libcxx/trunk/include/__threading_support

 
 #if defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
 # include <__external_threading>
 #elif !defined(_LIBCPP_HAS_NO_THREADS)
 
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 # include <pthread.h>
 # include <sched.h>
-#elif defined(_LIBCPP_HAS_THREAD_API_WIN32)
-#include <windows.h>
-#include <process.h>
-#include <fibersapi.h>
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
-
-#if defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL) || \
-    defined(_LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL)
-#define _LIBCPP_THREAD_ABI_VISIBILITY _LIBCPP_FUNC_VIS
-#else
-#define _LIBCPP_THREAD_ABI_VISIBILITY inline _LIBCPP_INLINE_VISIBILITY
-#endif
-
 #if defined(__FreeBSD__) && defined(__clang__) && __has_attribute(no_thread_safety_analysis)
 #define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS __attribute__((no_thread_safety_analysis))
 #else
 #define _LIBCPP_NO_THREAD_SAFETY_ANALYSIS
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
+#if defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL) || \
+    defined(_LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL)
+
+#define _LIBCPP_THREAD_ABI_VISIBILITY _LIBCPP_FUNC_VIS
+
+#elif defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
+
+#define _LIBCPP_THREAD_ABI_VISIBILITY inline _LIBCPP_INLINE_VISIBILITY
+
 // Mutex
 typedef pthread_mutex_t __libcpp_mutex_t;
 #define _LIBCPP_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
 
 typedef pthread_mutex_t __libcpp_recursive_mutex_t;
 
 // Condition Variable
 typedef pthread_cond_t __libcpp_condvar_t;

 
 typedef pthread_t __libcpp_thread_t;
 
 // Thrad Local Storage
 typedef pthread_key_t __libcpp_tls_key;
 
 #define _LIBCPP_TLS_DESTRUCTOR_CC
 #else
+
+#define _LIBCPP_THREAD_ABI_VISIBILITY _LIBCPP_FUNC_VIS
+
 // Mutex
-typedef SRWLOCK __libcpp_mutex_t;
-#define _LIBCPP_MUTEX_INITIALIZER SRWLOCK_INIT
+typedef void* __libcpp_mutex_t;
+#define _LIBCPP_MUTEX_INITIALIZER 0
 
-typedef CRITICAL_SECTION __libcpp_recursive_mutex_t;
+#if defined(_M_IX86) || defined(__i386__) || defined(_M_ARM) || defined(__arm__)
+typedef void* __libcpp_recursive_mutex_t[6];
+#elif defined(_M_AMD64) || defined(__x86_64__) || defined(_M_ARM64) || defined(__aarch64__)
+typedef void* __libcpp_recursive_mutex_t[5];
+#else
+# error Unsupported architecture
+#endif
 
 // Condition Variable
-typedef CONDITION_VARIABLE __libcpp_condvar_t;
-#define _LIBCPP_CONDVAR_INITIALIZER CONDITION_VARIABLE_INIT
+typedef void* __libcpp_condvar_t;
+#define _LIBCPP_CONDVAR_INITIALIZER 0
 
 // Execute Once
-typedef INIT_ONCE __libcpp_exec_once_flag;
-#define _LIBCPP_EXEC_ONCE_INITIALIZER INIT_ONCE_STATIC_INIT
+typedef void* __libcpp_exec_once_flag;
+#define _LIBCPP_EXEC_ONCE_INITIALIZER 0
 
 // Thread ID
-typedef DWORD __libcpp_thread_id;
+typedef long __libcpp_thread_id;
 
 // Thread
 #define _LIBCPP_NULL_THREAD 0U
 
-typedef HANDLE __libcpp_thread_t;
+typedef void* __libcpp_thread_t;
 
 // Thread Local Storage
-typedef DWORD __libcpp_tls_key;
+typedef long __libcpp_tls_key;
 
-#define _LIBCPP_TLS_DESTRUCTOR_CC WINAPI
+#define _LIBCPP_TLS_DESTRUCTOR_CC __stdcall
 #endif
 
 // Mutex
 _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m);
 
 _LIBCPP_THREAD_ABI_VISIBILITY _LIBCPP_NO_THREAD_SAFETY_ANALYSIS
 int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m);
int __libcpp_tls_create(__libcpp_tls_key* __key,
                         void(_LIBCPP_TLS_DESTRUCTOR_CC* __at_exit)(void*));
 
 _LIBCPP_THREAD_ABI_VISIBILITY
 void *__libcpp_tls_get(__libcpp_tls_key __key);
 
 _LIBCPP_THREAD_ABI_VISIBILITY
 int __libcpp_tls_set(__libcpp_tls_key __key, void *__p);
 
-#if !defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL) || \
-    defined(_LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL)
-
-#if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
+#if (!defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL) || \
+     defined(_LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL)) && \
+    defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 
 int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m)
 {
   pthread_mutexattr_t attr;
   int __ec = pthread_mutexattr_init(&attr);
   if (__ec)
     return __ec;
   __ec = pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
void *__libcpp_tls_get(__libcpp_tls_key __key)
   return pthread_getspecific(__key);
 }
 
 int __libcpp_tls_set(__libcpp_tls_key __key, void *__p)
 {
     return pthread_setspecific(__key, __p);
 }
 
-#elif defined(_LIBCPP_HAS_THREAD_API_WIN32)
-
-// Mutex
-int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m)
-{
-  InitializeCriticalSection(__m);
-  return 0;
-}
-
-int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m)
-{
-  EnterCriticalSection(__m);
-  return 0;
-}
-
-bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
-{
-  return TryEnterCriticalSection(__m) != 0;
-}
-
-int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t *__m)
-{
-  LeaveCriticalSection(__m);
-  return 0;
-}
-
-int __libcpp_recursive_mutex_destroy(__libcpp_recursive_mutex_t *__m)
-{
-  DeleteCriticalSection(__m);
-  return 0;
-}
-
-int __libcpp_mutex_lock(__libcpp_mutex_t *__m)
-{
-  AcquireSRWLockExclusive(__m);
-  return 0;
-}
-
-bool __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
-{
-  return TryAcquireSRWLockExclusive(__m) != 0;
-}
-
-int __libcpp_mutex_unlock(__libcpp_mutex_t *__m)
-{
-  ReleaseSRWLockExclusive(__m);
-  return 0;
-}
-
-int __libcpp_mutex_destroy(__libcpp_mutex_t *__m)
-{
-  static_cast<void>(__m);
-  return 0;
-}
-
-// Condition Variable
-int __libcpp_condvar_signal(__libcpp_condvar_t *__cv)
-{
-  WakeConditionVariable(__cv);
-  return 0;
-}
-
-int __libcpp_condvar_broadcast(__libcpp_condvar_t *__cv)
-{
-  WakeAllConditionVariable(__cv);
-  return 0;
-}
-
-int __libcpp_condvar_wait(__libcpp_condvar_t *__cv, __libcpp_mutex_t *__m)
-{
-  SleepConditionVariableSRW(__cv, __m, INFINITE, 0);
-  return 0;
-}
-
-int __libcpp_condvar_timedwait(__libcpp_condvar_t *__cv, __libcpp_mutex_t *__m,
-                               timespec *__ts)
-{
-  using namespace _VSTD::chrono;
-
-  auto duration = seconds(__ts->tv_sec) + nanoseconds(__ts->tv_nsec);
-  auto abstime =
-      system_clock::time_point(duration_cast<system_clock::duration>(duration));
-  auto timeout_ms = duration_cast<milliseconds>(abstime - system_clock::now());
-
-  if (!SleepConditionVariableSRW(__cv, __m,
-                                 timeout_ms.count() > 0 ? timeout_ms.count()
-                                                        : 0,
-                                 0))
-    {
-      auto __ec = GetLastError();
-      return __ec == ERROR_TIMEOUT ? ETIMEDOUT : __ec;
-    }
-  return 0;
-}
-
-int __libcpp_condvar_destroy(__libcpp_condvar_t *__cv)
-{
-  static_cast<void>(__cv);
-  return 0;
-}
-
-// Execute Once
-static inline _LIBCPP_ALWAYS_INLINE BOOL CALLBACK
-__libcpp_init_once_execute_once_thunk(PINIT_ONCE __init_once, PVOID __parameter,
-                                      PVOID *__context)
-{
-  static_cast<void>(__init_once);
-  static_cast<void>(__context);
-
-  void (*init_routine)(void) = reinterpret_cast<void (*)(void)>(__parameter);
-  init_routine();
-  return TRUE;
-}
-
-int __libcpp_execute_once(__libcpp_exec_once_flag *__flag,
-                          void (*__init_routine)(void))
-{
-  if (!InitOnceExecuteOnce(__flag, __libcpp_init_once_execute_once_thunk,
-                           reinterpret_cast<void *>(__init_routine), NULL))
-    return GetLastError();
-  return 0;
-}
-
-// Thread ID
-bool __libcpp_thread_id_equal(__libcpp_thread_id __lhs,
-                              __libcpp_thread_id __rhs)
-{
-  return __lhs == __rhs;
-}
-
-bool __libcpp_thread_id_less(__libcpp_thread_id __lhs, __libcpp_thread_id __rhs)
-{
-  return __lhs < __rhs;
-}
-
-// Thread
-struct __libcpp_beginthreadex_thunk_data
-{
-  void *(*__func)(void *);
-  void *__arg;
-};
-
-static inline _LIBCPP_ALWAYS_INLINE unsigned WINAPI
-__libcpp_beginthreadex_thunk(void *__raw_data)
-{
-  auto *__data =
-      static_cast<__libcpp_beginthreadex_thunk_data *>(__raw_data);
-  auto *__func = __data->__func;
-  void *__arg = __data->__arg;
-  delete __data;
-  return static_cast<unsigned>(reinterpret_cast<uintptr_t>(__func(__arg)));
-}
-
-bool __libcpp_thread_isnull(const __libcpp_thread_t *__t) {
-  return *__t == 0;
-}
-
-int __libcpp_thread_create(__libcpp_thread_t *__t, void *(*__func)(void *),
-                           void *__arg)
-{
-  auto *__data = new __libcpp_beginthreadex_thunk_data;
-  __data->__func = __func;
-  __data->__arg = __arg;
-
-  *__t = reinterpret_cast<HANDLE>(_beginthreadex(nullptr, 0,
-                                                 __libcpp_beginthreadex_thunk,
-                                                 __data, 0, nullptr));
-
-  if (*__t)
-    return 0;
-  return GetLastError();
-}
-
-__libcpp_thread_id __libcpp_thread_get_current_id()
-{
-  return GetCurrentThreadId();
-}
-
-__libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t *__t)
-{
-  return GetThreadId(*__t);
-}
-
-int __libcpp_thread_join(__libcpp_thread_t *__t)
-{
-  if (WaitForSingleObjectEx(*__t, INFINITE, FALSE) == WAIT_FAILED)
-    return GetLastError();
-  if (!CloseHandle(*__t))
-    return GetLastError();
-  return 0;
-}
-
-int __libcpp_thread_detach(__libcpp_thread_t *__t)
-{
-  if (!CloseHandle(*__t))
-    return GetLastError();
-  return 0;
-}
-
-void __libcpp_thread_yield()
-{
-  SwitchToThread();
-}
-
-void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns)
-{
-  using namespace chrono;
-  // round-up to the nearest milisecond
-  milliseconds __ms =
-      duration_cast<milliseconds>(__ns + chrono::nanoseconds(999999));
-  // FIXME(compnerd) this should be an alertable sleep (WFSO or SleepEx)
-  Sleep(__ms.count());
-}
-
-// Thread Local Storage
-int __libcpp_tls_create(__libcpp_tls_key* __key,
-                        void(_LIBCPP_TLS_DESTRUCTOR_CC* __at_exit)(void*))
-{
-  *__key = FlsAlloc(__at_exit);
-  if (*__key == FLS_OUT_OF_INDEXES)
-    return GetLastError();
-  return 0;
-}
-
-void *__libcpp_tls_get(__libcpp_tls_key __key)
-{
-  return FlsGetValue(__key);
-}
-
-int __libcpp_tls_set(__libcpp_tls_key __key, void *__p)
-{
-  if (!FlsSetValue(__key, __p))
-    return GetLastError();
-  return 0;
-}
-
-#endif // _LIBCPP_HAS_THREAD_API_PTHREAD
-
 #endif // !_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL || _LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // !_LIBCPP_HAS_NO_THREADS
 
 #endif // _LIBCPP_THREADING_SUPPORT

libcxx/trunk/src/support/win32/thread_win32.cpp

+// -*- C++ -*-
+//===-------------------- support/win32/thread_win32.cpp ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <__threading_support>
+#include <windows.h>
+#include <process.h>
+#include <fibersapi.h>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+static_assert(sizeof(__libcpp_mutex_t) == sizeof(SRWLOCK), "");
+static_assert(alignof(__libcpp_mutex_t) == alignof(SRWLOCK), "");
+
+static_assert(sizeof(__libcpp_recursive_mutex_t) == sizeof(CRITICAL_SECTION),
+              "");
+static_assert(alignof(__libcpp_recursive_mutex_t) == alignof(CRITICAL_SECTION),
+              "");
+
+static_assert(sizeof(__libcpp_condvar_t) == sizeof(CONDITION_VARIABLE), "");
+static_assert(alignof(__libcpp_condvar_t) == alignof(CONDITION_VARIABLE), "");
+
+static_assert(sizeof(__libcpp_exec_once_flag) == sizeof(INIT_ONCE), "");
+static_assert(alignof(__libcpp_exec_once_flag) == alignof(INIT_ONCE), "");
+
+static_assert(sizeof(__libcpp_thread_id) == sizeof(DWORD), "");
+static_assert(alignof(__libcpp_thread_id) == alignof(DWORD), "");
+
+static_assert(sizeof(__libcpp_thread_t) == sizeof(HANDLE), "");
+static_assert(alignof(__libcpp_thread_t) == alignof(HANDLE), "");
+
+static_assert(sizeof(__libcpp_tls_key) == sizeof(DWORD), "");
+static_assert(alignof(__libcpp_tls_key) == alignof(DWORD), "");
+
+// Mutex
+int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m)
+{
+  InitializeCriticalSection((LPCRITICAL_SECTION)__m);
+  return 0;
+}
+
+int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t *__m)
+{
+  EnterCriticalSection((LPCRITICAL_SECTION)__m);
+  return 0;
+}
+
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t *__m)
+{
+  return TryEnterCriticalSection((LPCRITICAL_SECTION)__m) != 0;
+}
+
+int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t *__m)
+{
+  LeaveCriticalSection((LPCRITICAL_SECTION)__m);
+  return 0;
+}
+
+int __libcpp_recursive_mutex_destroy(__libcpp_recursive_mutex_t *__m)
+{
+  DeleteCriticalSection((LPCRITICAL_SECTION)__m);
+  return 0;
+}
+
+int __libcpp_mutex_lock(__libcpp_mutex_t *__m)
+{
+  AcquireSRWLockExclusive((PSRWLOCK)__m);
+  return 0;
+}
+
+bool __libcpp_mutex_trylock(__libcpp_mutex_t *__m)
+{
+  return TryAcquireSRWLockExclusive((PSRWLOCK)__m) != 0;
+}
+
+int __libcpp_mutex_unlock(__libcpp_mutex_t *__m)
+{
+  ReleaseSRWLockExclusive((PSRWLOCK)__m);
+  return 0;
+}
+
+int __libcpp_mutex_destroy(__libcpp_mutex_t *__m)
+{
+  static_cast<void>(__m);
+  return 0;
+}
+
+// Condition Variable
+int __libcpp_condvar_signal(__libcpp_condvar_t *__cv)
+{
+  WakeConditionVariable((PCONDITION_VARIABLE)__cv);
+  return 0;
+}
+
+int __libcpp_condvar_broadcast(__libcpp_condvar_t *__cv)
+{
+  WakeAllConditionVariable((PCONDITION_VARIABLE)__cv);
+  return 0;
+}
+
+int __libcpp_condvar_wait(__libcpp_condvar_t *__cv, __libcpp_mutex_t *__m)
+{
+  SleepConditionVariableSRW((PCONDITION_VARIABLE)__cv, (PSRWLOCK)__m, INFINITE, 0);
+  return 0;
+}
+
+int __libcpp_condvar_timedwait(__libcpp_condvar_t *__cv, __libcpp_mutex_t *__m,
+                               timespec *__ts)
+{
+  using namespace _VSTD::chrono;
+
+  auto duration = seconds(__ts->tv_sec) + nanoseconds(__ts->tv_nsec);
+  auto abstime =
+      system_clock::time_point(duration_cast<system_clock::duration>(duration));
+  auto timeout_ms = duration_cast<milliseconds>(abstime - system_clock::now());
+
+  if (!SleepConditionVariableSRW((PCONDITION_VARIABLE)__cv, (PSRWLOCK)__m,
+                                 timeout_ms.count() > 0 ? timeout_ms.count()
+                                                        : 0,
+                                 0))
+    {
+      auto __ec = GetLastError();
+      return __ec == ERROR_TIMEOUT ? ETIMEDOUT : __ec;
+    }
+  return 0;
+}
+
+int __libcpp_condvar_destroy(__libcpp_condvar_t *__cv)
+{
+  static_cast<void>(__cv);
+  return 0;
+}
+
+// Execute Once
+static inline _LIBCPP_ALWAYS_INLINE BOOL CALLBACK
+__libcpp_init_once_execute_once_thunk(PINIT_ONCE __init_once, PVOID __parameter,
+                                      PVOID *__context)
+{
+  static_cast<void>(__init_once);
+  static_cast<void>(__context);
+
+  void (*init_routine)(void) = reinterpret_cast<void (*)(void)>(__parameter);
+  init_routine();
+  return TRUE;
+}
+
+int __libcpp_execute_once(__libcpp_exec_once_flag *__flag,
+                          void (*__init_routine)(void))
+{
+  if (!InitOnceExecuteOnce((PINIT_ONCE)__flag, __libcpp_init_once_execute_once_thunk,
+                           reinterpret_cast<void *>(__init_routine), NULL))
+    return GetLastError();
+  return 0;
+}
+
+// Thread ID
+bool __libcpp_thread_id_equal(__libcpp_thread_id __lhs,
+                              __libcpp_thread_id __rhs)
+{
+  return __lhs == __rhs;
+}
+
+bool __libcpp_thread_id_less(__libcpp_thread_id __lhs, __libcpp_thread_id __rhs)
+{
+  return __lhs < __rhs;
+}
+
+// Thread
+struct __libcpp_beginthreadex_thunk_data
+{
+  void *(*__func)(void *);
+  void *__arg;
+};
+
+static inline _LIBCPP_ALWAYS_INLINE unsigned WINAPI
+__libcpp_beginthreadex_thunk(void *__raw_data)
+{
+  auto *__data =
+      static_cast<__libcpp_beginthreadex_thunk_data *>(__raw_data);
+  auto *__func = __data->__func;
+  void *__arg = __data->__arg;
+  delete __data;
+  return static_cast<unsigned>(reinterpret_cast<uintptr_t>(__func(__arg)));
+}
+
+bool __libcpp_thread_isnull(const __libcpp_thread_t *__t) {
+  return *__t == 0;
+}
+
+int __libcpp_thread_create(__libcpp_thread_t *__t, void *(*__func)(void *),
+                           void *__arg)
+{
+  auto *__data = new __libcpp_beginthreadex_thunk_data;
+  __data->__func = __func;
+  __data->__arg = __arg;
+
+  *__t = reinterpret_cast<HANDLE>(_beginthreadex(nullptr, 0,
+                                                 __libcpp_beginthreadex_thunk,
+                                                 __data, 0, nullptr));
+
+  if (*__t)
+    return 0;
+  return GetLastError();
+}
+
+__libcpp_thread_id __libcpp_thread_get_current_id()
+{
+  return GetCurrentThreadId();
+}
+
+__libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t *__t)
+{
+  return GetThreadId(*__t);
+}
+
+int __libcpp_thread_join(__libcpp_thread_t *__t)
+{
+  if (WaitForSingleObjectEx(*__t, INFINITE, FALSE) == WAIT_FAILED)
+    return GetLastError();
+  if (!CloseHandle(*__t))
+    return GetLastError();
+  return 0;
+}
+
+int __libcpp_thread_detach(__libcpp_thread_t *__t)
+{
+  if (!CloseHandle(*__t))
+    return GetLastError();
+  return 0;
+}
+
+void __libcpp_thread_yield()
+{
+  SwitchToThread();
+}
+
+void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns)
+{
+  using namespace chrono;
+  // round-up to the nearest milisecond
+  milliseconds __ms =
+      duration_cast<milliseconds>(__ns + chrono::nanoseconds(999999));
+  // FIXME(compnerd) this should be an alertable sleep (WFSO or SleepEx)
+  Sleep(__ms.count());
+}
+
+// Thread Local Storage
+int __libcpp_tls_create(__libcpp_tls_key* __key,
+                        void(_LIBCPP_TLS_DESTRUCTOR_CC* __at_exit)(void*))
+{
+  *__key = FlsAlloc(__at_exit);
+  if (*__key == FLS_OUT_OF_INDEXES)
+    return GetLastError();
+  return 0;
+}
+
+void *__libcpp_tls_get(__libcpp_tls_key __key)
+{
+  return FlsGetValue(__key);
+}
+
+int __libcpp_tls_set(__libcpp_tls_key __key, void *__p)
+{
+  if (!FlsSetValue(__key, __p))
+    return GetLastError();
+  return 0;
+}
+
+_LIBCPP_END_NAMESPACE_STD