[netcore] Implement Thread.GetCurrentProcessorId (mono/mono#18450)

CoreCLR has a managed cache surrounding this, but for the moment the naive implementation will suffice. We can later move their managed cache to shared on top of this PR with minimal trouble.

We can't guarantee the id will be [0..CpuCount) for a variety of reasons, and a followup PR to the dotnet docs will clarify this. I've chosen not to intentionally add an offset, but no one should be relying on that behavior, and if someone thinks adding an offset would drive the point home the perf cost is irrelevant.

Commit migrated from mono/mono@3b19228

src/mono/mono/metadata/icall-def-netcore.h

@@ -492,6 +492,7 @@ ICALL_TYPE(THREAD, "System.Threading.Thread", THREAD_1)
 HANDLES(THREAD_1, "ClrState", ves_icall_System_Threading_Thread_ClrState, void, 2, (MonoInternalThread, guint32))
 HANDLES(ITHREAD_2, "FreeInternal", ves_icall_System_Threading_InternalThread_Thread_free_internal, void, 1, (MonoInternalThread))
 HANDLES(THREAD_15, "GetCurrentOSThreadId", ves_icall_System_Threading_Thread_GetCurrentOSThreadId, guint64, 0, ())
+HANDLES(THREAD_16, "GetCurrentProcessorNumber", ves_icall_System_Threading_Thread_GetCurrentProcessorNumber, gint32, 0, ())
 HANDLES(THREAD_3, "GetState", ves_icall_System_Threading_Thread_GetState, guint32, 1, (MonoInternalThread))
 HANDLES(THREAD_4, "InitInternal", ves_icall_System_Threading_Thread_InitInternal, void, 1, (MonoThreadObject))
 HANDLES(THREAD_5, "InitializeCurrentThread", ves_icall_System_Threading_Thread_GetCurrentThread, MonoThreadObject, 0, ())

src/mono/mono/metadata/threads.c

@@ -6768,4 +6768,10 @@ ves_icall_System_Threading_Thread_GetCurrentOSThreadId (MonoError *error)
 	return mono_native_thread_os_id_get ();
 }
 
+gint32
+ves_icall_System_Threading_Thread_GetCurrentProcessorNumber (MonoError *error)
+{
+	return mono_native_thread_processor_id_get ();
+}
+
 #endif

src/mono/mono/utils/mono-threads-posix.c

@@ -336,6 +336,16 @@ mono_memory_barrier_process_wide (void)
 	g_assert (status == 0);
 }
 
+gint32
+mono_native_thread_processor_id_get (void)
+{
+#ifdef HAVE_SCHED_GETCPU
+	return sched_getcpu ();
+#else
+	return -1;
+#endif
+}
+
 #endif /* defined(_POSIX_VERSION) */
 
 #if defined(USE_POSIX_BACKEND)

src/mono/mono/utils/mono-threads-wasm.c

@@ -110,6 +110,12 @@ mono_native_thread_os_id_get (void)
 #endif
 }
 
+gint32
+mono_native_thread_processor_id_get (void)
+{
+	return -1;
+}
+
 MONO_API gboolean
 mono_native_thread_create (MonoNativeThreadId *tid, gpointer func, gpointer arg)
 {

src/mono/mono/utils/mono-threads-windows.c

@@ -412,6 +412,14 @@ mono_native_thread_os_id_get (void)
 	return (guint64)GetCurrentThreadId ();
 }
 
+gint32
+mono_native_thread_processor_id_get (void)
+{
+	PROCESSOR_NUMBER proc_num;
+	GetCurrentProcessorNumberEx (&proc_num);
+	return ((proc_num.Group << 6) | proc_num.Number);
+}
+
 gboolean
 mono_native_thread_id_equals (MonoNativeThreadId id1, MonoNativeThreadId id2)
 {

src/mono/mono/utils/mono-threads.h

@@ -641,6 +641,8 @@ mono_native_thread_id_get (void);
  */
 guint64 mono_native_thread_os_id_get (void);
 
+gint32 mono_native_thread_processor_id_get (void);
+
 MONO_API gboolean
 mono_native_thread_id_equals (MonoNativeThreadId id1, MonoNativeThreadId id2);
 

src/mono/netcore/System.Private.CoreLib/src/System/Threading/Thread.Mono.cs

@@ -163,10 +163,17 @@ public void DisableComObjectEagerCleanup ()
 			// no-op
 		}
 
+		[MethodImplAttribute(MethodImplOptions.InternalCall)]
+		extern static int GetCurrentProcessorNumber ();		
+
 		public static int GetCurrentProcessorId ()
 		{
-			// TODO: Implement correctly
-			return Environment.CurrentManagedThreadId;
+			int id = GetCurrentProcessorNumber ();
+
+			if (id < 0)
+				id = Environment.CurrentManagedThreadId;
+
+			return id;
 		}
 
 		public void Interrupt ()