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py/runtime: Fix mp_unpack_ex so seq can't be reclaimed by GC during use. 

The issue described in the comment added here can be seen by forcing a
gc_collect() at the start of each call to gc_alloc().
This commit is contained in:
Damien George 2019-04-15 11:30:19 +10:00
parent 3fa06cf61e
commit 9ce25d7022
1 changed files with 6 additions and 1 deletions
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7
py/runtime.c
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@ -875,8 +875,12 @@ void mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
DEBUG_OP_printf("unpack ex " UINT_FMT " " UINT_FMT "\n", num_left, num_right); DEBUG_OP_printf("unpack ex " UINT_FMT " " UINT_FMT "\n", num_left, num_right);
size_t seq_len; size_t seq_len;
if (mp_obj_is_type(seq_in, &mp_type_tuple) || mp_obj_is_type(seq_in, &mp_type_list)) { if (mp_obj_is_type(seq_in, &mp_type_tuple) || mp_obj_is_type(seq_in, &mp_type_list)) {
// Make the seq variable volatile so the compiler keeps a reference to it,
// since if it's a tuple then seq_items points to the interior of the GC cell
// and mp_obj_new_list may trigger a GC which doesn't trace this and reclaims seq.
volatile mp_obj_t seq = seq_in;
mp_obj_t *seq_items; mp_obj_t *seq_items;
mp_obj_get_array(seq_in, &seq_len, &seq_items); mp_obj_get_array(seq, &seq_len, &seq_items);
if (seq_len < num_left + num_right) { if (seq_len < num_left + num_right) {
goto too_short; goto too_short;
} }
@ -887,6 +891,7 @@ void mp_unpack_ex(mp_obj_t seq_in, size_t num_in, mp_obj_t *items) {
for (size_t i = 0; i < num_left; i++) { for (size_t i = 0; i < num_left; i++) {
items[num_right + 1 + i] = seq_items[num_left - 1 - i]; items[num_right + 1 + i] = seq_items[num_left - 1 - i];
} }
seq = MP_OBJ_NULL;
} else { } else {
// Generic iterable; this gets a bit messy: we unpack known left length to the // Generic iterable; this gets a bit messy: we unpack known left length to the
// items destination array, then the rest to a dynamically created list. Once the // items destination array, then the rest to a dynamically created list. Once the