1 files changed, 22 insertions, 7 deletions
diff --git a/contrib/libc++/src/thread.cpp b/contrib/libc++/src/thread.cpp
index b2bd07e9d3ba..1fd8bb047c89 100644
--- a/contrib/libc++/src/thread.cpp
+++ b/contrib/libc++/src/thread.cpp
@@ -13,14 +13,20 @@
 #include "future"
 #include "limits"
 #include <sys/types.h>
-#if !_WIN32
-#if !__sun__ && !__linux__
+#if !defined(_WIN32)
+#if !defined(__sun__) && !defined(__linux__)
 #include <sys/sysctl.h>
-#else
-#include <unistd.h>
 #endif // !__sun__ && !__linux__
+#include <unistd.h>
 #endif // !_WIN32
 
+#if defined(__NetBSD__)
+#pragma weak pthread_create // Do not create libpthread dependency
+#endif
+#if defined(_WIN32)
+#include <windows.h>
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 thread::~thread()
@@ -36,6 +42,8 @@ thread::join()
 #ifndef _LIBCPP_NO_EXCEPTIONS
     if (ec)
         throw system_error(error_code(ec, system_category()), "thread::join failed");
+#else
+    (void)ec;
 #endif  // _LIBCPP_NO_EXCEPTIONS
     __t_ = 0;
 }
@@ -65,16 +73,23 @@ thread::hardware_concurrency() _NOEXCEPT
     std::size_t s = sizeof(n);
     sysctl(mib, 2, &n, &s, 0, 0);
     return n;
-#elif defined(_POSIX_C_SOURCE) && (_POSIX_C_SOURCE >= 200112L) && defined(_SC_NPROCESSORS_ONLN)
+#elif defined(_SC_NPROCESSORS_ONLN)
     long result = sysconf(_SC_NPROCESSORS_ONLN);
     // sysconf returns -1 if the name is invalid, the option does not exist or
     // does not have a definite limit.
-    if (result == -1)
+    // if sysconf returns some other negative number, we have no idea
+    // what is going on. Default to something safe.
+    if (result < 0)
         return 0;
-    return result;
+    return static_cast<unsigned>(result);
+#elif defined(_WIN32)
+    SYSTEM_INFO info;
+    GetSystemInfo(&info);
+    return info.dwNumberOfProcessors;
 #else  // defined(CTL_HW) && defined(HW_NCPU)
     // TODO: grovel through /proc or check cpuid on x86 and similar
     // instructions on other architectures.
+#warning hardware_concurrency not yet implemented
     return 0;  // Means not computable [thread.thread.static]
 #endif  // defined(CTL_HW) && defined(HW_NCPU)
 }