Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/SystemInfo.cs

@@ -0,0 +1,61 @@
+//------------------------------------------------------------------------------
+// <copyright file="SystemInfo.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+
+    internal static class SystemInfo {
+        static int  _trueNumberOfProcessors;
+
+        static internal int GetNumProcessCPUs() {
+            if (_trueNumberOfProcessors == 0) {
+                UnsafeNativeMethods.SYSTEM_INFO si;
+                UnsafeNativeMethods.GetSystemInfo(out si);
+
+                if (si.dwNumberOfProcessors == 1) {
+                    _trueNumberOfProcessors = 1;
+                }
+                else {
+                    // KERNEL32.DLL:GetCurrentProcess() always returns -1 under NT
+                    // Note: not really a handle (no need to CloseHandle())
+                    IntPtr processHandle = UnsafeNativeMethods.INVALID_HANDLE_VALUE;
+                    IntPtr processAffinityMask;
+                    IntPtr systemAffinityMask;
+                    int returnCode = UnsafeNativeMethods.GetProcessAffinityMask(
+                            processHandle, out processAffinityMask, out systemAffinityMask);
+
+                    if (returnCode == 0) {
+                        _trueNumberOfProcessors = 1;
+                    }
+                    else {
+                        // if cpu affinity is set to a single processor busy waiting is a waste of time
+                        int numProcessors = 0;
+                        if (IntPtr.Size == 4) {
+                            uint mask = (uint) processAffinityMask;
+                            for (; mask != 0; mask >>= 1) {
+                                if ((mask & 1) == 1) {
+                                    ++numProcessors;
+                                }
+                            }
+                        }
+                        else {
+                            ulong mask = (ulong) processAffinityMask;
+                            for (; mask != 0; mask >>= 1) {
+                                if ((mask & 1) == 1) {
+                                    ++numProcessors;
+                                }
+                            }
+                        }
+
+                        _trueNumberOfProcessors = numProcessors;
+                    }
+                }
+            }
+
+            Debug.Assert(_trueNumberOfProcessors > 0);
+            return _trueNumberOfProcessors;
+        }
+    }
+}