py: Add mp_pending_exception global variable, for VM soft interrupt.

This allows to implement KeyboardInterrupt on unix, and a much safer
ctrl-C in stmhal port.  First ctrl-C is a soft one, with hope that VM
will notice it; second ctrl-C is a hard one that kills anything (for
both unix and stmhal).

One needs to check for a pending exception in the VM only for jump
opcodes.  Others can't produce an infinite loop (infinite recursion is
caught by stack check).

1 files changed, 27 insertions, 0 deletions

diff --git a/unix/main.c b/unix/main.c
index a8de9fdee3..44542af51b 100644
--- a/unix/main.c
+++ b/unix/main.c
@@ -34,6 +34,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <errno.h>
+#include <signal.h>
 
 #include "mpconfig.h"
 #include "nlr.h"
@@ -64,6 +65,20 @@ mp_uint_t mp_verbose_flag = 0;
 long heap_size = 128*1024 * (sizeof(mp_uint_t) / 4);
 #endif
 
+STATIC mp_obj_t keyboard_interrupt_obj;
+
+STATIC void sighandler(int signum) {
+    if (signum == SIGINT) {
+        mp_obj_exception_clear_traceback(keyboard_interrupt_obj);
+        mp_pending_exception = keyboard_interrupt_obj;
+        // disable our handler so next we really die
+        struct sigaction sa;
+        sa.sa_handler = SIG_DFL;
+        sigemptyset(&sa.sa_mask);
+        sigaction(SIGINT, &sa, NULL);
+    }
+}
+
 #define FORCED_EXIT (0x100)
 // returns standard error codes: 0 for success, 1 for all other errors
 // if FORCED_EXIT bit is set then script raised SystemExit and the
@@ -119,14 +134,23 @@ STATIC int execute_from_lexer(mp_lexer_t *lex, mp_parse_input_kind_t input_kind,
         return 0;
     }
 
+    // enable signal handler
+    struct sigaction sa;
+    sa.sa_handler = sighandler;
+    sigemptyset(&sa.sa_mask);
+    sigaction(SIGINT, &sa, NULL);
+    sa.sa_handler = SIG_DFL;
+
     // execute it
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
         mp_call_function_0(module_fun);
+        sigaction(SIGINT, &sa, NULL);
         nlr_pop();
         return 0;
     } else {
         // uncaught exception
+        sigaction(SIGINT, &sa, NULL);
         // check for SystemExit
         mp_obj_t exc = (mp_obj_t)nlr.ret_val;
         if (mp_obj_is_subclass_fast(mp_obj_get_type(exc), &mp_type_SystemExit)) {
@@ -305,6 +329,9 @@ int main(int argc, char **argv) {
 
     mp_init();
 
+    // create keyboard interrupt object
+    keyboard_interrupt_obj = mp_obj_new_exception(&mp_type_KeyboardInterrupt);
+
     char *home = getenv("HOME");
     char *path = getenv("MICROPYPATH");
     if (path == NULL) {