objgenerator: Implement .throw() method to throw exceptions into generator.

py/bc.h

@@ -15,5 +15,5 @@ typedef struct _mp_exc_stack {
 } mp_exc_stack;
 
 mp_vm_return_kind_t mp_execute_byte_code(const byte *code, const mp_obj_t *args, uint n_args, const mp_obj_t *args2, uint n_args2, uint n_state, mp_obj_t *ret);
-mp_vm_return_kind_t mp_execute_byte_code_2(const byte *code_info, const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out, mp_exc_stack *exc_stack, mp_exc_stack **exc_sp_in_out);
+mp_vm_return_kind_t mp_execute_byte_code_2(const byte *code_info, const byte **ip_in_out, mp_obj_t *fastn, mp_obj_t **sp_in_out, mp_exc_stack *exc_stack, mp_exc_stack **exc_sp_in_out, volatile mp_obj_t inject_exc);
 void mp_byte_code_print(const byte *code, int len);

py/objgenerator.c

@@ -70,7 +70,7 @@ mp_obj_t gen_instance_getiter(mp_obj_t self_in) {
     return self_in;
 }
 
-STATIC mp_obj_t gen_next_send(mp_obj_t self_in, mp_obj_t send_value) {
+STATIC mp_obj_t gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value) {
     mp_obj_gen_instance_t *self = self_in;
     if (self->ip == 0) {
         return mp_const_stop_iteration;
@@ -83,7 +83,8 @@ STATIC mp_obj_t gen_next_send(mp_obj_t self_in, mp_obj_t send_value) {
         *self->sp = send_value;
     }
     mp_vm_return_kind_t vm_return_kind = mp_execute_byte_code_2(self->code_info, &self->ip,
-        &self->state[self->n_state - 1], &self->sp, (mp_exc_stack*)(self->state + self->n_state), &self->exc_sp);
+        &self->state[self->n_state - 1], &self->sp, (mp_exc_stack*)(self->state + self->n_state),
+        &self->exc_sp, throw_value);
     switch (vm_return_kind) {
         case MP_VM_RETURN_NORMAL:
             // Explicitly mark generator as completed. If we don't do this,
@@ -113,11 +114,11 @@ STATIC mp_obj_t gen_next_send(mp_obj_t self_in, mp_obj_t send_value) {
 }
 
 mp_obj_t gen_instance_iternext(mp_obj_t self_in) {
-    return gen_next_send(self_in, mp_const_none);
+    return gen_resume(self_in, mp_const_none, MP_OBJ_NULL);
 }
 
 STATIC mp_obj_t gen_instance_send(mp_obj_t self_in, mp_obj_t send_value) {
-    mp_obj_t ret = gen_next_send(self_in, send_value);
+    mp_obj_t ret = gen_resume(self_in, send_value, MP_OBJ_NULL);
     if (ret == mp_const_stop_iteration) {
         nlr_jump(mp_obj_new_exception(&mp_type_StopIteration));
     } else {
@@ -127,8 +128,21 @@ STATIC mp_obj_t gen_instance_send(mp_obj_t self_in, mp_obj_t send_value) {
 
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(gen_instance_send_obj, gen_instance_send);
 
+STATIC mp_obj_t gen_instance_throw(uint n_args, const mp_obj_t *args) {
+    mp_obj_t ret = gen_resume(args[0], mp_const_none, n_args == 2 ? args[1] : args[2]);
+    if (ret == mp_const_stop_iteration) {
+        nlr_jump(mp_obj_new_exception(&mp_type_StopIteration));
+    } else {
+        return ret;
+    }
+}
+
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(gen_instance_throw_obj, 2, 4, gen_instance_throw);
+
+
 STATIC const mp_method_t gen_type_methods[] = {
     { "send", &gen_instance_send_obj },
+    { "throw", &gen_instance_throw_obj },
     { NULL, NULL }, // end-of-list sentinel
 };
 

py/vm.c

@@ -82,7 +82,7 @@ mp_vm_return_kind_t mp_execute_byte_code(const byte *code, const mp_obj_t *args,
     mp_exc_stack exc_stack[4];
     mp_exc_stack *exc_sp = &exc_stack[0] - 1;
     // execute the byte code
-    mp_vm_return_kind_t vm_return_kind = mp_execute_byte_code_2(code, &ip, &state[n_state - 1], &sp, exc_stack, &exc_sp);
+    mp_vm_return_kind_t vm_return_kind = mp_execute_byte_code_2(code, &ip, &state[n_state - 1], &sp, exc_stack, &exc_sp, MP_OBJ_NULL);
 
     switch (vm_return_kind) {
         case MP_VM_RETURN_NORMAL:
@@ -107,8 +107,8 @@ mp_vm_return_kind_t mp_execute_byte_code(const byte *code, const mp_obj_t *args,
 //  MP_VM_RETURN_EXCEPTION, exception in fastn[0]
 mp_vm_return_kind_t mp_execute_byte_code_2(const byte *code_info, const byte **ip_in_out,
                                            mp_obj_t *fastn, mp_obj_t **sp_in_out,
-                                           mp_exc_stack *exc_stack,
-                                           mp_exc_stack **exc_sp_in_out) {
+                                           mp_exc_stack *exc_stack, mp_exc_stack **exc_sp_in_out,
+                                           volatile mp_obj_t inject_exc) {
     // careful: be sure to declare volatile any variables read in the exception handler (written is ok, I think)
 
     const byte *ip = *ip_in_out;
@@ -118,13 +118,21 @@ mp_vm_return_kind_t mp_execute_byte_code_2(const byte *code_info, const byte **i
     mp_obj_t obj1, obj2;
     nlr_buf_t nlr;
 
-    volatile machine_uint_t currently_in_except_block = 0; // 0 or 1, to detect nested exceptions
-    mp_exc_stack *volatile exc_sp = *exc_sp_in_out; // stack grows up, exc_sp points to top of stack
+    volatile machine_uint_t currently_in_except_block = (int)*exc_sp_in_out & 1; // 0 or 1, to detect nested exceptions
+    mp_exc_stack *volatile exc_sp = (void*)((int)*exc_sp_in_out & ~1); // stack grows up, exc_sp points to top of stack
     const byte *volatile save_ip = ip; // this is so we can access ip in the exception handler without making ip volatile (which means the compiler can't keep it in a register in the main loop)
 
     // outer exception handling loop
     for (;;) {
         if (nlr_push(&nlr) == 0) {
+            // If we have exception to inject, now that we finish setting up
+            // execution context, raise it. This works as if RAISE_VARARGS
+            // bytecode was executed.
+            if (inject_exc != MP_OBJ_NULL) {
+                mp_obj_t t = inject_exc;
+                inject_exc = MP_OBJ_NULL;
+                nlr_jump(rt_make_raise_obj(t));
+            }
             // loop to execute byte code
             for (;;) {
 dispatch_loop:
@@ -599,7 +607,7 @@ unwind_return:
                         nlr_pop();
                         *ip_in_out = ip;
                         *sp_in_out = sp;
-                        *exc_sp_in_out = exc_sp;
+                        *exc_sp_in_out = (void*)((int)exc_sp | currently_in_except_block);
                         return MP_VM_RETURN_YIELD;
 
                     case MP_BC_IMPORT_NAME:

tests/basics/generator-exc.py

@@ -29,3 +29,25 @@ try:
     print(next(g))
 except StopIteration:
     print("StopIteration")
+
+
+# Test throwing exception into generator
+def gen3():
+    yield 1
+    try:
+        yield 2
+    except ValueError:
+        print("ValueError received")
+        yield 3
+    yield 4
+    yield 5
+
+g = gen3()
+print(next(g))
+print(next(g))
+print("out of throw:", g.throw(ValueError))
+print(next(g))
+try:
+    print("out of throw2:", g.throw(ValueError))
+except ValueError:
+    print("Boomerang ValueError caught")