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unix/modffi: Add option to lock GC in callback, and cfun access.
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Add an optional 'lock' kwarg to callback that locks GC and scheduler.  This
allows the callback to be invoked asynchronously in 'interrupt context',
for example as a signal handler.

Also add the 'cfun' member function to callback, that allows retrieving the
C callback function address.  This is needed when the callback should be
set to a struct field.

See related #7373.

Signed-off-by: Amir Gonnen <amirgonnen@gmail.com>
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@amirgon @dpgeorge
amirgon authored and dpgeorge committed Jun 24, 2021
1 parent 413f34c commit cb332dd
Showing 1 changed file with 71 additions and 5 deletions.
76 changes: 71 additions & 5 deletions ports/unix/modffi.c
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Expand Up @@ -36,6 +36,7 @@
#include "py/binary.h"
#include "py/mperrno.h"
#include "py/objint.h"
#include "py/gc.h"

/*
* modffi uses character codes to encode a value type, based on "struct"
Expand Down Expand Up @@ -100,6 +101,7 @@ typedef struct _mp_obj_fficallback_t {
void *func;
ffi_closure *clo;
char rettype;
mp_obj_t pyfunc;
ffi_cif cif;
ffi_type *params[];
} mp_obj_fficallback_t;
Expand Down Expand Up @@ -266,19 +268,69 @@ STATIC mp_obj_t mod_ffi_func(mp_obj_t rettype, mp_obj_t addr_in, mp_obj_t argtyp
}
MP_DEFINE_CONST_FUN_OBJ_3(mod_ffi_func_obj, mod_ffi_func);

STATIC void call_py_func(ffi_cif *cif, void *ret, void **args, void *func) {
STATIC void call_py_func(ffi_cif *cif, void *ret, void **args, void *user_data) {
mp_obj_t pyargs[cif->nargs];
mp_obj_fficallback_t *o = user_data;
mp_obj_t pyfunc = o->pyfunc;

for (uint i = 0; i < cif->nargs; i++) {
pyargs[i] = mp_obj_new_int(*(mp_int_t *)args[i]);
}
mp_obj_t res = mp_call_function_n_kw(MP_OBJ_FROM_PTR(func), cif->nargs, 0, pyargs);
mp_obj_t res = mp_call_function_n_kw(pyfunc, cif->nargs, 0, pyargs);

if (res != mp_const_none) {
*(ffi_arg *)ret = mp_obj_int_get_truncated(res);
}
}

STATIC mp_obj_t mod_ffi_callback(mp_obj_t rettype_in, mp_obj_t func_in, mp_obj_t paramtypes_in) {
STATIC void call_py_func_with_lock(ffi_cif *cif, void *ret, void **args, void *user_data) {
mp_obj_t pyargs[cif->nargs];
mp_obj_fficallback_t *o = user_data;
mp_obj_t pyfunc = o->pyfunc;
nlr_buf_t nlr;

#if MICROPY_ENABLE_SCHEDULER
mp_sched_lock();
#endif
gc_lock();

if (nlr_push(&nlr) == 0) {
for (uint i = 0; i < cif->nargs; i++) {
pyargs[i] = mp_obj_new_int(*(mp_int_t *)args[i]);
}
mp_obj_t res = mp_call_function_n_kw(pyfunc, cif->nargs, 0, pyargs);

if (res != mp_const_none) {
*(ffi_arg *)ret = mp_obj_int_get_truncated(res);
}
nlr_pop();
} else {
// Uncaught exception
mp_printf(MICROPY_ERROR_PRINTER, "Uncaught exception in FFI callback\n");
mp_obj_print_exception(MICROPY_ERROR_PRINTER, MP_OBJ_FROM_PTR(nlr.ret_val));
}

gc_unlock();
#if MICROPY_ENABLE_SCHEDULER
mp_sched_unlock();
#endif
}

STATIC mp_obj_t mod_ffi_callback(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
// first 3 args are positional: retttype, func, paramtypes.
mp_obj_t rettype_in = pos_args[0];
mp_obj_t func_in = pos_args[1];
mp_obj_t paramtypes_in = pos_args[2];

// arg parsing is used only for additional kwargs
enum { ARG_lock };
static const mp_arg_t allowed_args[] = {
{ MP_QSTR_lock, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
};
mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
mp_arg_parse_all(n_args - 3, pos_args + 3, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
bool lock_in = args[ARG_lock].u_bool;

const char *rettype = mp_obj_str_get_str(rettype_in);

mp_int_t nparams = MP_OBJ_SMALL_INT_VALUE(mp_obj_len_maybe(paramtypes_in));
Expand All @@ -288,6 +340,7 @@ STATIC mp_obj_t mod_ffi_callback(mp_obj_t rettype_in, mp_obj_t func_in, mp_obj_t
o->clo = ffi_closure_alloc(sizeof(ffi_closure), &o->func);

o->rettype = *rettype;
o->pyfunc = func_in;

mp_obj_iter_buf_t iter_buf;
mp_obj_t iterable = mp_getiter(paramtypes_in, &iter_buf);
Expand All @@ -302,14 +355,15 @@ STATIC mp_obj_t mod_ffi_callback(mp_obj_t rettype_in, mp_obj_t func_in, mp_obj_t
mp_raise_ValueError(MP_ERROR_TEXT("error in ffi_prep_cif"));
}

res = ffi_prep_closure_loc(o->clo, &o->cif, call_py_func, MP_OBJ_TO_PTR(func_in), o->func);
res = ffi_prep_closure_loc(o->clo, &o->cif,
lock_in? call_py_func_with_lock: call_py_func, o, o->func);
if (res != FFI_OK) {
mp_raise_ValueError(MP_ERROR_TEXT("ffi_prep_closure_loc"));
}

return MP_OBJ_FROM_PTR(o);
}
MP_DEFINE_CONST_FUN_OBJ_3(mod_ffi_callback_obj, mod_ffi_callback);
MP_DEFINE_CONST_FUN_OBJ_KW(mod_ffi_callback_obj, 3, mod_ffi_callback);

STATIC mp_obj_t ffimod_var(mp_obj_t self_in, mp_obj_t vartype_in, mp_obj_t symname_in) {
mp_obj_ffimod_t *self = MP_OBJ_TO_PTR(self_in);
Expand Down Expand Up @@ -493,10 +547,22 @@ STATIC void fficallback_print(const mp_print_t *print, mp_obj_t self_in, mp_prin
mp_printf(print, "<fficallback %p>", self->func);
}

STATIC mp_obj_t fficallback_cfun(mp_obj_t self_in) {
mp_obj_fficallback_t *self = MP_OBJ_TO_PTR(self_in);
return mp_obj_new_int_from_ull((uintptr_t)self->func);
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(fficallback_cfun_obj, fficallback_cfun);

STATIC const mp_rom_map_elem_t fficallback_locals_dict_table[] = {
{ MP_ROM_QSTR(MP_QSTR_cfun), MP_ROM_PTR(&fficallback_cfun_obj) }
};
STATIC MP_DEFINE_CONST_DICT(fficallback_locals_dict, fficallback_locals_dict_table);

STATIC const mp_obj_type_t fficallback_type = {
{ &mp_type_type },
.name = MP_QSTR_fficallback,
.print = fficallback_print,
.locals_dict = (mp_obj_dict_t *)&fficallback_locals_dict
};

// FFI variable
Expand Down

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