Add a utility cache line size constant

SConstruct

@@ -851,6 +851,7 @@ if env.msvc and not methods.using_clang(env):  # MSVC
                 "/wd4245",
                 "/wd4267",
                 "/wd4305",  # C4305 (truncation): double to float or real_t, too hard to avoid.
+                "/wd4324",  # C4820 (structure was padded due to alignment specifier)
                 "/wd4514",  # C4514 (unreferenced inline function has been removed)
                 "/wd4714",  # C4714 (function marked as __forceinline not inlined)
                 "/wd4820",  # C4820 (padding added after construct)

core/os/thread.h

@@ -42,6 +42,8 @@
 #include "core/templates/safe_refcount.h"
 #include "core/typedefs.h"
 
+#include <new>
+
 #ifdef MINGW_ENABLED
 #define MINGW_STDTHREAD_REDUNDANCY_WARNING
 #include "thirdparty/mingw-std-threads/mingw.thread.h"
@@ -85,6 +87,20 @@ public:
 		void (*term)() = nullptr;
 	};
 
+#if defined(__cpp_lib_hardware_interference_size) && !defined(ANDROID_ENABLED) // This would be OK with NDK >= 26.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Winterference-size"
+#endif
+	static constexpr size_t CACHE_LINE_BYTES = std::hardware_destructive_interference_size;
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
+#else
+	// At a negligible memory cost, we use a conservatively high value.
+	static constexpr size_t CACHE_LINE_BYTES = 128;
+#endif
+
 private:
 	friend class Main;
 
@@ -135,6 +151,8 @@ public:
 
 	typedef uint64_t ID;
 
+	static constexpr size_t CACHE_LINE_BYTES = sizeof(void *);
+
 	enum : ID {
 		UNASSIGNED_ID = 0,
 		MAIN_ID = 1