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py/objgenerator: Allow to pend an exception for next execution.
This implements .pend_throw(exc) method, which sets up an exception to be triggered on the next call to generator's .__next__() or .send() method. This is unlike .throw(), which immediately starts to execute the generator to process the exception. This effectively adds Future-like capabilities to generator protocol (exception will be raised in the future). The need for such a method arised to implement uasyncio wait_for() function efficiently (its behavior is clearly "Future" like, and normally would require to introduce an expensive Future wrapper around all native couroutines, like upstream asyncio does). py/objgenerator: pend_throw: Return previous pended value. This effectively allows to store an additional value (not necessary an exception) in a coroutine while it's not being executed. uasyncio has exactly this usecase: to mark a coro waiting in I/O queue (and thus not executed in the normal scheduling queue), for the purpose of implementing wait_for() function (cancellation of such waiting coro by a timeout).
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Lines changed: 68 additions & 3 deletions

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‎py/mpconfig.h‎

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Original file line numberDiff line numberDiff line change
@@ -706,6 +706,15 @@ typedef double mp_float_t;
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#define MICROPY_PY_ASYNC_AWAIT (1)
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#endif
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// Non-standard .pend_throw() method for generators, allowing for
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// Future-like behavior with respect to exception handling: an
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// exception set with .pend_throw() will activate on the next call
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// to generator's .send() or .__next__(). (This is useful to implement
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// async schedulers.)
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#ifndef MICROPY_PY_GENERATOR_PEND_THROW
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#define MICROPY_PY_GENERATOR_PEND_THROW (1)
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#endif
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// Issue a warning when comparing str and bytes objects
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#ifndef MICROPY_PY_STR_BYTES_CMP_WARN
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#define MICROPY_PY_STR_BYTES_CMP_WARN (0)

‎py/objgenerator.c‎

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@@ -4,7 +4,7 @@
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* The MIT License (MIT)
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*
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* Copyright (c) 2013, 2014 Damien P. George
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* Copyright (c) 2014 Paul Sokolovsky
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* Copyright (c) 2014-2017 Paul Sokolovsky
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
@@ -104,7 +104,16 @@ mp_vm_return_kind_t mp_obj_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_
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mp_raise_TypeError("can't send non-None value to a just-started generator");
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}
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} else {
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*self->code_state.sp = send_value;
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#if MICROPY_PY_GENERATOR_PEND_THROW
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// If exception is pending (set using .pend_throw()), process it now.
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if (*self->code_state.sp != mp_const_none) {
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throw_value = *self->code_state.sp;
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*self->code_state.sp = MP_OBJ_NULL;
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} else
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#endif
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{
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*self->code_state.sp = send_value;
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}
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}
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mp_obj_dict_t *old_globals = mp_globals_get();
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mp_globals_set(self->globals);
@@ -125,6 +134,9 @@ mp_vm_return_kind_t mp_obj_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_
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case MP_VM_RETURN_YIELD:
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*ret_val = *self->code_state.sp;
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#if MICROPY_PY_GENERATOR_PEND_THROW
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*self->code_state.sp = mp_const_none;
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#endif
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break;
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case MP_VM_RETURN_EXCEPTION: {
@@ -219,10 +231,24 @@ STATIC mp_obj_t gen_instance_close(mp_obj_t self_in) {
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STATIC MP_DEFINE_CONST_FUN_OBJ_1(gen_instance_close_obj, gen_instance_close);
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STATIC mp_obj_t gen_instance_pend_throw(mp_obj_t self_in, mp_obj_t exc_in) {
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mp_obj_gen_instance_t *self = MP_OBJ_TO_PTR(self_in);
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if (self->code_state.sp == self->code_state.state - 1) {
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mp_raise_TypeError("can't pend throw to just-started generator");
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}
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mp_obj_t prev = *self->code_state.sp;
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*self->code_state.sp = exc_in;
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return prev;
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}
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STATIC MP_DEFINE_CONST_FUN_OBJ_2(gen_instance_pend_throw_obj, gen_instance_pend_throw);
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STATIC const mp_rom_map_elem_t gen_instance_locals_dict_table[] = {
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{ MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&gen_instance_close_obj) },
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{ MP_ROM_QSTR(MP_QSTR_send), MP_ROM_PTR(&gen_instance_send_obj) },
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{ MP_ROM_QSTR(MP_QSTR_throw), MP_ROM_PTR(&gen_instance_throw_obj) },
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#if MICROPY_PY_GENERATOR_PEND_THROW
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{ MP_ROM_QSTR(MP_QSTR_pend_throw), MP_ROM_PTR(&gen_instance_pend_throw_obj) },
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#endif
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};
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STATIC MP_DEFINE_CONST_DICT(gen_instance_locals_dict, gen_instance_locals_dict_table);

‎tests/basics/generator_pend_throw.py‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,26 @@
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def gen():
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i = 0
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while 1:
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yield i
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i += 1
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g = gen()
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try:
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g.pend_throw
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except AttributeError:
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print("SKIP")
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raise SystemExit
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print(next(g))
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print(next(g))
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g.pend_throw(ValueError())
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v = None
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try:
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v = next(g)
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except Exception as e:
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print("raised", repr(e))
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print("ret was:", v)

‎tests/basics/generator_pend_throw.py.exp‎

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0
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raised ValueError()
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ret was: None

‎tests/run-tests‎

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@@ -337,7 +337,7 @@ def run_tests(pyb, tests, args, base_path="."):
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# Some tests are known to fail with native emitter
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# Remove them from the below when they work
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if args.emit == 'native':
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skip_tests.update({'basics/%s.py' % t for t in 'gen_yield_from gen_yield_from_close gen_yield_from_ducktype gen_yield_from_exc gen_yield_from_iter gen_yield_from_send gen_yield_from_stopped gen_yield_from_throw gen_yield_from_throw2 gen_yield_from_throw3 generator1 generator2 generator_args generator_close generator_closure generator_exc generator_return generator_send'.split()}) # require yield
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skip_tests.update({'basics/%s.py' % t for t in 'gen_yield_from gen_yield_from_close gen_yield_from_ducktype gen_yield_from_exc gen_yield_from_iter gen_yield_from_send gen_yield_from_stopped gen_yield_from_throw gen_yield_from_throw2 gen_yield_from_throw3 generator1 generator2 generator_args generator_close generator_closure generator_exc generator_pend_throw generator_return generator_send'.split()}) # require yield
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skip_tests.update({'basics/%s.py' % t for t in 'bytes_gen class_store_class globals_del string_join'.split()}) # require yield
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skip_tests.update({'basics/async_%s.py' % t for t in 'def await await2 for for2 with with2'.split()}) # require yield
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skip_tests.update({'basics/%s.py' % t for t in 'try_reraise try_reraise2'.split()}) # require raise_varargs

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