py/scheduler: Implement VM abort flag and mp_sched_vm_abort().

This is intended to be used by the very outer caller of the VM/runtime.  It
allows setting a top-level NLR handler that can be jumped to directly, in
order to forcefully abort the VM/runtime.

Enable using:

    #define MICROPY_ENABLE_VM_ABORT (1)

Set up the handler at the top level using:

    nlr_buf_t nlr;
    nlr.ret_val = NULL;
    if (nlr_push(&nlr) == 0) {
        nlr_set_abort(&nlr);
        // call into the VM/runtime
        ...
        nlr_pop();
    } else {
        if (nlr.ret_val == NULL) {
            // handle abort
            ...
        } else {
            // handle other exception that propagated to the top level
            ...
        }
    }
    nlr_set_abort(NULL);

Schedule an abort, eg from an interrupt handler, using:

    mp_sched_vm_abort();

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/py/scheduler.c b/py/scheduler.c
index db090b099..165b26dc8 100644
--- a/py/scheduler.c
+++ b/py/scheduler.c
@@ -51,6 +51,12 @@ void MICROPY_WRAP_MP_SCHED_KEYBOARD_INTERRUPT(mp_sched_keyboard_interrupt)(void)
 }
 #endif
 
+#if MICROPY_ENABLE_VM_ABORT
+void MICROPY_WRAP_MP_SCHED_VM_ABORT(mp_sched_vm_abort)(void) {
+    MP_STATE_VM(vm_abort) = true;
+}
+#endif
+
 #if MICROPY_ENABLE_SCHEDULER
 
 #define IDX_MASK(i) ((i) & (MICROPY_SCHEDULER_DEPTH - 1))
@@ -203,6 +209,17 @@ MP_REGISTER_ROOT_POINTER(mp_sched_item_t sched_queue[MICROPY_SCHEDULER_DEPTH]);
 // Called periodically from the VM or from "waiting" code (e.g. sleep) to
 // process background tasks and pending exceptions (e.g. KeyboardInterrupt).
 void mp_handle_pending(bool raise_exc) {
+    // Handle pending VM abort.
+    #if MICROPY_ENABLE_VM_ABORT
+    if (MP_STATE_VM(vm_abort) && mp_thread_is_main_thread()) {
+        MP_STATE_VM(vm_abort) = false;
+        if (raise_exc && nlr_get_abort() != NULL) {
+            nlr_jump_abort();
+        }
+    }
+    #endif
+
+    // Handle any pending exception.
     if (MP_STATE_THREAD(mp_pending_exception) != MP_OBJ_NULL) {
         mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
         mp_obj_t obj = MP_STATE_THREAD(mp_pending_exception);
@@ -215,6 +232,8 @@ void mp_handle_pending(bool raise_exc) {
         }
         MICROPY_END_ATOMIC_SECTION(atomic_state);
     }
+
+    // Handle any pending callbacks.
     #if MICROPY_ENABLE_SCHEDULER
     if (MP_STATE_VM(sched_state) == MP_SCHED_PENDING) {
         mp_sched_run_pending();