Re: implementation of std::thread::hardware_concurrency()

[Marc Glisse]

On Tue, 1 Nov 2011, niXman wrote:

diff --git a/libstdc++-v3/src/thread.cc b/libstdc++-v3/src/thread.cc
index 09e7fc5..6feda4d 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 defined(_GLIBCXX_USE_GET_NPROCS)
+    count=_GLIBCXX_NPROCS;
+#endif
+    return (count>0)?count:0;

Er, the macro _GLIBCXX_NPROCS already handles the case 
sysconf(_SC_NPROCESSORS_ONLN). It looks like you actually want to remove 
the macro _GLIBCXX_NPROCS completely.

--
Marc Glisse