Bug 1546544 - Reduce navigator.hardwareConcurrency to account for TCSM r=luke

Differential Revision: https://phabricator.services.mozilla.com/D29437

--HG--
extra : moz-landing-system : lando

dom/workers/RuntimeService.cpp

@@ -71,6 +71,10 @@
 #include "OSFileConstants.h"
 #include "xpcpublic.h"
 
+#if defined(XP_MACOSX)
+# include "nsMacUtilsImpl.h"
+#endif
+
 #include "Principal.h"
 #include "WorkerDebuggerManager.h"
 #include "WorkerError.h"
@@ -2150,7 +2154,17 @@ uint32_t RuntimeService::ClampedHardwareConcurrency() const {
   // No need to loop here: if compareExchange fails, that just means that some
   // other worker has initialized numberOfProcessors, so we're good to go.
   if (!clampedHardwareConcurrency) {
-    int32_t numberOfProcessors = PR_GetNumberOfProcessors();
+    int32_t numberOfProcessors = 0;
+#if defined(XP_MACOSX)
+    if (nsMacUtilsImpl::IsTCSMAvailable()) {
+      // On failure, zero is returned from GetPhysicalCPUCount()
+      // and we fallback to PR_GetNumberOfProcessors below.
+      numberOfProcessors = nsMacUtilsImpl::GetPhysicalCPUCount();
+    }
+#endif
+    if (numberOfProcessors == 0) {
+      numberOfProcessors = PR_GetNumberOfProcessors();
+    }
     if (numberOfProcessors <= 0) {
       numberOfProcessors = 1;  // Must be one there somewhere
     }

dom/workers/moz.build

@@ -80,6 +80,12 @@ LOCAL_INCLUDES += [
     '/xpcom/threads',
 ]
 
+if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa':
+    LOCAL_INCLUDES += [
+        '/xpcom/base',
+    ]
+
+
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'

xpcom/base/nsMacUtilsImpl.cpp

@@ -303,3 +303,15 @@ bool nsMacUtilsImpl::IsTCSMEnabled() {
   return (rv == 0) && (oldVal != 0);
 }
 #endif
+
+// Returns 0 on error.
+/* static */
+uint32_t nsMacUtilsImpl::GetPhysicalCPUCount() {
+  uint32_t oldVal = 0;
+  size_t oldValSize = sizeof(oldVal);
+  int rv = sysctlbyname("hw.physicalcpu_max", &oldVal, &oldValSize, NULL, 0);
+  if (rv == -1) {
+    return 0;
+  }
+  return oldVal;
+}

xpcom/base/nsMacUtilsImpl.h

@@ -36,6 +36,8 @@ class nsMacUtilsImpl final : public nsIMacUtils {
 #endif   /* MOZ_SANDBOX */
 
   static void EnableTCSMIfAvailable();
+  static bool IsTCSMAvailable();
+  static uint32_t GetPhysicalCPUCount();
 
  private:
   ~nsMacUtilsImpl() {}
@@ -60,7 +62,6 @@ class nsMacUtilsImpl final : public nsIMacUtils {
   };
   static mozilla::Atomic<nsMacUtilsImpl::TCSMStatus> sTCSMStatus;
 
-  static bool IsTCSMAvailable();
   static nsresult EnableTCSM();
 #if defined(DEBUG)
   static bool IsTCSMEnabled();