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py: Fix memoryview referencing so it retains ptr to original buffer.

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This way, if original parent object is GC'd, the memoryview still points
to the underlying buffer data so that buffer is not GC'd.
This commit is contained in:
Damien George 2014-10-26 13:20:50 +00:00
parent c76af32575
commit de3c806965
2 changed files with 74 additions and 24 deletions
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70
py/objarray.c
View File

@ -39,12 +39,32 @@
#if MICROPY_PY_ARRAY || MICROPY_PY_BUILTINS_BYTEARRAY || MICROPY_PY_BUILTINS_MEMORYVIEW
// About memoryview object: We want to reuse as much code as possible from
// array, and keep the memoryview object 4 words in size so it fits in 1 GC
// block. Also, memoryview must keep a pointer to the base of the buffer so
// that the buffer is not GC'd if the original parent object is no longer
// around (we are assuming that all memoryview'able objects return a pointer
// which points to the start of a GC chunk). Given the above constraints we
// do the following:
// - typecode high bit is set if the buffer is read-write (else read-only)
// - free is the offset in elements to the first item in the memoryview
// - len is the length in elements
// - items points to the start of the original buffer
// Note that we don't handle the case where the original buffer might change
// size due to a resize of the original parent object.
// make (& TYPECODE_MASK) a null operation if memorview not enabled
#if MICROPY_PY_BUILTINS_MEMORYVIEW
#define TYPECODE_MASK (0x7f)
#else
#define TYPECODE_MASK (~(mp_uint_t)1)
#endif
typedef struct _mp_obj_array_t {
mp_obj_base_t base;
mp_uint_t typecode : 8;
// free is number of unused elements after len used elements
// alloc size = len + free
// for memoryview, free=0 is read-only, free=1 is read-write
mp_uint_t free : (8 * sizeof(mp_uint_t) - 8);
mp_uint_t len; // in elements
void *items;
@ -187,7 +207,7 @@ STATIC mp_obj_t memoryview_make_new(mp_obj_t type_in, mp_uint_t n_args, mp_uint_
// test if the object can be written to
if (mp_get_buffer(args[0], &bufinfo, MP_BUFFER_RW)) {
self->free = 1; // used to indicate writable buffer
self->typecode |= 0x80; // used to indicate writable buffer
}
return self;
@ -259,7 +279,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
"only slices with step=1 (aka None) are supported"));
}
mp_obj_array_t *res;
int sz = mp_binary_get_size('@', o->typecode, NULL);
int sz = mp_binary_get_size('@', o->typecode & TYPECODE_MASK, NULL);
assert(sz > 0);
if (0) {
// dummy
@ -267,8 +287,8 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
} else if (o->base.type == &mp_type_memoryview) {
res = m_new_obj(mp_obj_array_t);
*res = *o;
res->free += slice.start;
res->len = slice.stop - slice.start;
res->items += slice.start * sz;
#endif
} else {
res = array_new(o->typecode, slice.stop - slice.start);
@ -278,18 +298,21 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
#endif
} else {
mp_uint_t index = mp_get_index(o->base.type, o->len, index_in, false);
if (value == MP_OBJ_SENTINEL) {
// load
return mp_binary_get_val_array(o->typecode, o->items, index);
} else {
// store
#if MICROPY_PY_BUILTINS_MEMORYVIEW
if (o->base.type == &mp_type_memoryview && o->free == 0) {
// read-only memoryview
if (o->base.type == &mp_type_memoryview) {
index += o->free;
if (value != MP_OBJ_SENTINEL && (o->typecode & 0x80) == 0) {
// store to read-only memoryview
return MP_OBJ_NULL;
}
}
#endif
mp_binary_set_val_array(o->typecode, o->items, index, value);
if (value == MP_OBJ_SENTINEL) {
// load
return mp_binary_get_val_array(o->typecode & TYPECODE_MASK, o->items, index);
} else {
// store
mp_binary_set_val_array(o->typecode & TYPECODE_MASK, o->items, index, value);
return mp_const_none;
}
}
@ -298,15 +321,19 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
STATIC mp_int_t array_get_buffer(mp_obj_t o_in, mp_buffer_info_t *bufinfo, mp_uint_t flags) {
mp_obj_array_t *o = o_in;
int sz = mp_binary_get_size('@', o->typecode & TYPECODE_MASK, NULL);
bufinfo->buf = o->items;
bufinfo->len = o->len * sz;
bufinfo->typecode = o->typecode & TYPECODE_MASK;
#if MICROPY_PY_BUILTINS_MEMORYVIEW
if (o->base.type == &mp_type_memoryview && o->free == 0 && (flags & MP_BUFFER_WRITE)) {
if (o->base.type == &mp_type_memoryview) {
if ((o->typecode & 0x80) == 0 && (flags & MP_BUFFER_WRITE)) {
// read-only memoryview
return 1;
}
bufinfo->buf += (mp_uint_t)o->free * sz;
}
#endif
bufinfo->buf = o->items;
bufinfo->len = o->len * mp_binary_get_size('@', o->typecode, NULL);
bufinfo->typecode = o->typecode;
return 0;
}
@ -392,13 +419,14 @@ mp_obj_t mp_obj_new_bytearray_by_ref(mp_uint_t n, void *items) {
typedef struct _mp_obj_array_it_t {
mp_obj_base_t base;
mp_obj_array_t *array;
mp_uint_t offset;
mp_uint_t cur;
} mp_obj_array_it_t;
STATIC mp_obj_t array_it_iternext(mp_obj_t self_in) {
mp_obj_array_it_t *self = self_in;
if (self->cur < self->array->len) {
return mp_binary_get_val_array(self->array->typecode, self->array->items, self->cur++);
return mp_binary_get_val_array(self->array->typecode & TYPECODE_MASK, self->array->items, self->offset + self->cur++);
} else {
return MP_OBJ_STOP_ITERATION;
}
@ -413,10 +441,14 @@ STATIC const mp_obj_type_t array_it_type = {
STATIC mp_obj_t array_iterator_new(mp_obj_t array_in) {
mp_obj_array_t *array = array_in;
mp_obj_array_it_t *o = m_new_obj(mp_obj_array_it_t);
mp_obj_array_it_t *o = m_new0(mp_obj_array_it_t, 1);
o->base.type = &array_it_type;
o->array = array;
o->cur = 0;
#if MICROPY_PY_BUILTINS_MEMORYVIEW
if (array->base.type == &mp_type_memoryview) {
o->offset = array->free;
}
#endif
return o;
}

18
tests/basics/memoryview_gc.py Normal file
View File

@ -0,0 +1,18 @@
# test memoryview retains pointer to original object/buffer
b = bytearray(10)
m = memoryview(b)[1:]
for i in range(len(m)):
m[i] = i
# reclaim b, but hopefully not the buffer
b = None
import gc
gc.collect()
# allocate lots of memory
for i in range(100000):
[42, 42, 42, 42]
# check that the memoryview is still what we want
print(list(m))