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, 5 insertions, 0 deletions

diff --git a/py/mpstate.h b/py/mpstate.h
index 4c9380097..f6b911af5 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -226,6 +226,11 @@ typedef struct _mp_state_vm_t {
     uint8_t sched_idx;
     #endif
 
+    #if MICROPY_ENABLE_VM_ABORT
+    bool vm_abort;
+    nlr_buf_t *nlr_abort;
+    #endif
+
     #if MICROPY_PY_THREAD_GIL
     // This is a global mutex used to make the VM/runtime thread-safe.
     mp_thread_mutex_t gil_mutex;