implementation of std::thread::hardware_concurrency()

[niXman]

Hi all.

This is patch is implement the std::thread::hardware_concurrency().
Tested on pthreads-win32/winpthreads on windows OS, and on Linux/FreeBSD.




diff --git a/libstdc++-v3/src/thread.cc b/libstdc++-v3/src/thread.cc
index 09e7fc5..3eacb06 100644
--- a/libstdc++-v3/src/thread.cc
+++ b/libstdc++-v3/src/thread.cc
@@ -112,10 +112,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   unsigned int
   thread::hardware_concurrency() noexcept
   {
-    int __n = _GLIBCXX_NPROCS;
-    if (__n < 0)
-      __n = 0;
-    return __n;
+    int count=0;
+#if defined(PTW32_VERSION) || \
+   (defined(__MINGW64_VERSION_MAJOR) && defined(_POSIX_THREADS)) || \
+   defined(__hpux)
+    count=pthread_num_processors_np();
+#elif defined(__APPLE__) || defined(__FreeBSD__)
+    size_t size=sizeof(count);
+    sysctlbyname("hw.ncpu", &count, &size, NULL, 0);
+#elif defined(_SC_NPROCESSORS_ONLN)
+    count=sysconf(_SC_NPROCESSORS_ONLN);
+#elif definen(_GLIBCXX_USE_GET_NPROCS)
+    count=_GLIBCXX_NPROCS;
+#endif
+    return (count>0)?count:0;
   }

 _GLIBCXX_END_NAMESPACE_VERSION