get proper number of physical cpu cores on macOS (#6835)

* get proper number of physical cpu cores on macOS

macOS has an easy way to get the physical cpu count so let's use it. Also with
Apple Silicon there are performance and efficiency cores so we need to make
sure we ignore those low-perf cores when getting the count.

* improve error handling

Author: notimaginative

code/utils/threading.cpp

@@ -11,6 +11,8 @@
 
 #ifdef WIN32
 #include <windows.h>
+#elif defined(__APPLE__)
+#include <sys/sysctl.h>
 #endif
 
 namespace threading {
@@ -85,6 +87,27 @@ namespace threading {
 			return num_cores;
 		}
 	}
+#elif defined __APPLE__
+	static size_t get_number_of_physical_cores() {
+		int rval = 0;
+		int num = 0;
+		size_t numSize = sizeof(num);
+
+		// apple silicon (performance cores only)
+		rval = sysctlbyname("hw.perflevel0.physicalcpu", &num, &numSize, nullptr, 0);
+
+		// intel
+		if (rval != 0) {
+			rval = sysctlbyname("hw.physicalcpu", &num, &numSize, nullptr, 0);
+		}
+
+		if (rval == 0 && num > 0) {
+			return num;
+		} else {
+			// invalid results, try fallback
+			return get_number_of_physical_cores_fallback();
+		}
+	}
 #elif defined SCP_UNIX
 	static size_t get_number_of_physical_cores() {
 		try {
@@ -170,4 +193,4 @@ namespace threading {
 	size_t get_num_workers() {
 		return worker_threads.size();
 	}
-}
+}