py/mpstate: Schedule KeyboardInterrupt on main thread.

This introduces a new macro to get the main thread and uses it to ensure
that asynchronous exceptions such as KeyboardInterrupt (CTRL+C) are only
scheduled on the main thread. This is more deterministic than being
scheduled on a random thread and is more in line with CPython that only
allow signal handlers to run on the main thread.

Fixes issue #7026.

Signed-off-by: David Lechner <david@pybricks.com>

ports/pic16bit/board.c

@@ -140,7 +140,7 @@ int switch_get(int sw) {
 // TODO need an irq
 void uart_rx_irq(void) {
     if (c == interrupt_char) {
-        MP_STATE_THREAD(mp_pending_exception) = MP_STATE_PORT(keyboard_interrupt_obj);
+        MP_STATE_MAIN_THREAD(mp_pending_exception) = MP_STATE_PORT(keyboard_interrupt_obj);
     }
 }
 */

ports/stm32/pendsv.c

@@ -60,10 +60,10 @@ void pendsv_init(void) {
 // the given exception object using nlr_jump in the context of the top-level
 // thread.
 void pendsv_kbd_intr(void) {
-    if (MP_STATE_THREAD(mp_pending_exception) == MP_OBJ_NULL) {
+    if (MP_STATE_MAIN_THREAD(mp_pending_exception) == MP_OBJ_NULL) {
         mp_sched_keyboard_interrupt();
     } else {
-        MP_STATE_THREAD(mp_pending_exception) = MP_OBJ_NULL;
+        MP_STATE_MAIN_THREAD(mp_pending_exception) = MP_OBJ_NULL;
         pendsv_object = &MP_STATE_VM(mp_kbd_exception);
         SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
     }

ports/unix/unix_mphal.c

@@ -54,7 +54,7 @@ STATIC void sighandler(int signum) {
         sigprocmask(SIG_SETMASK, &mask, NULL);
         nlr_raise(MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception)));
         #else
-        if (MP_STATE_THREAD(mp_pending_exception) == MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception))) {
+        if (MP_STATE_MAIN_THREAD(mp_pending_exception) == MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception))) {
             // this is the second time we are called, so die straight away
             exit(1);
         }

ports/windows/windows_mphal.c

@@ -80,7 +80,7 @@ void mp_hal_stdio_mode_orig(void) {
 // the thread created for handling it might not be running yet so we'd miss the notification.
 BOOL WINAPI console_sighandler(DWORD evt) {
     if (evt == CTRL_C_EVENT) {
-        if (MP_STATE_THREAD(mp_pending_exception) == MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception))) {
+        if (MP_STATE_MAIN_THREAD(mp_pending_exception) == MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception))) {
             // this is the second time we are called, so die straight away
             exit(1);
         }

py/mpstate.h

@@ -285,12 +285,13 @@ extern mp_state_ctx_t mp_state_ctx;
 
 #define MP_STATE_VM(x) (mp_state_ctx.vm.x)
 #define MP_STATE_MEM(x) (mp_state_ctx.mem.x)
+#define MP_STATE_MAIN_THREAD(x) (mp_state_ctx.thread.x)
 
 #if MICROPY_PY_THREAD
 extern mp_state_thread_t *mp_thread_get_state(void);
 #define MP_STATE_THREAD(x) (mp_thread_get_state()->x)
 #else
-#define MP_STATE_THREAD(x) (mp_state_ctx.thread.x)
+#define MP_STATE_THREAD(x)  MP_STATE_MAIN_THREAD(x)
 #endif
 
 #endif // MICROPY_INCLUDED_PY_MPSTATE_H

py/scheduler.c

@@ -28,8 +28,10 @@
 
 #include "py/runtime.h"
 
+// Schedules an exception on the main thread (for exceptions "thrown" by async
+// sources such as interrupts and UNIX signal handlers).
 void MICROPY_WRAP_MP_SCHED_EXCEPTION(mp_sched_exception)(mp_obj_t exc) {
-    MP_STATE_THREAD(mp_pending_exception) = exc;
+    MP_STATE_MAIN_THREAD(mp_pending_exception) = exc;
     #if MICROPY_ENABLE_SCHEDULER
     if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE) {
         MP_STATE_VM(sched_state) = MP_SCHED_PENDING;