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Issue #12778: Reduce memory consumption when JSON-encoding a large container of many small objects.

This commit is contained in:
Antoine Pitrou 2011-08-19 18:03:14 +02:00
parent 9bb6dfe0a8
commit df7fc9dda7
3 changed files with 175 additions and 50 deletions
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19
Lib/test/json_tests/test_dump.py
View File

@ -1,6 +1,7 @@
from io import StringIO
from test.json_tests import PyTest, CTest
from test.support import precisionbigmemtest, _1G
class TestDump:
def test_dump(self):
@ -21,4 +22,20 @@ class TestDump:
class TestPyDump(TestDump, PyTest): pass
class TestCDump(TestDump, CTest): pass
class TestCDump(TestDump, CTest):
# The size requirement here is hopefully over-estimated (actual
# memory consumption depending on implementation details, and also
# system memory management, since this may allocate a lot of
# small objects).
@precisionbigmemtest(size=_1G, memuse=1)
def test_large_list(self, size):
N = int(30 * 1024 * 1024 * (size / _1G))
l = [1] * N
encoded = self.dumps(l)
self.assertEqual(len(encoded), N * 3)
self.assertEqual(encoded[:1], "[")
self.assertEqual(encoded[-2:], "1]")
self.assertEqual(encoded[1:-2], "1, " * (N - 1))

3
Misc/NEWS
View File

@ -262,6 +262,9 @@ Core and Builtins
Library
-------
- Issue #12778: Reduce memory consumption when JSON-encoding a large
container of many small objects.
- Issue #12650: Fix a race condition where a subprocess.Popen could leak
resources (FD/zombie) when killed at the wrong time.

203
Modules/_json.c
View File

@ -75,6 +75,121 @@ static PyMemberDef encoder_members[] = {
{NULL}
};
/*
* A two-level accumulator of unicode objects that avoids both the overhead
* of keeping a huge number of small separate objects, and the quadratic
* behaviour of using a naive repeated concatenation scheme.
*/
typedef struct {
PyObject *large; /* A list of previously accumulated large strings */
PyObject *small; /* Pending small strings */
} accumulator;
static PyObject *
join_list_unicode(PyObject *lst)
{
/* return u''.join(lst) */
static PyObject *sep = NULL;
if (sep == NULL) {
sep = PyUnicode_FromStringAndSize("", 0);
if (sep == NULL)
return NULL;
}
return PyUnicode_Join(sep, lst);
}
static int
init_accumulator(accumulator *acc)
{
acc->large = PyList_New(0);
if (acc->large == NULL)
return -1;
acc->small = PyList_New(0);
if (acc->small == NULL) {
Py_CLEAR(acc->large);
return -1;
}
return 0;
}
static int
flush_accumulator(accumulator *acc)
{
Py_ssize_t nsmall = PyList_GET_SIZE(acc->small);
if (nsmall) {
int ret;
PyObject *joined = join_list_unicode(acc->small);
if (joined == NULL)
return -1;
if (PyList_SetSlice(acc->small, 0, nsmall, NULL)) {
Py_DECREF(joined);
return -1;
}
ret = PyList_Append(acc->large, joined);
Py_DECREF(joined);
return ret;
}
return 0;
}
static int
accumulate_unicode(accumulator *acc, PyObject *obj)
{
int ret;
Py_ssize_t nsmall;
assert(PyUnicode_Check(obj));
if (PyList_Append(acc->small, obj))
return -1;
nsmall = PyList_GET_SIZE(acc->small);
/* Each item in a list of unicode objects has an overhead (in 64-bit
* builds) of:
* - 8 bytes for the list slot
* - 56 bytes for the header of the unicode object
* that is, 64 bytes. 100000 such objects waste more than 6MB
* compared to a single concatenated string.
*/
if (nsmall < 100000)
return 0;
PyObject *joined = join_list_unicode(acc->small);
if (joined == NULL)
return -1;
if (PyList_SetSlice(acc->small, 0, nsmall, NULL)) {
Py_DECREF(joined);
return -1;
}
ret = PyList_Append(acc->large, joined);
Py_DECREF(joined);
return ret;
}
static PyObject *
finish_accumulator(accumulator *acc)
{
int ret;
PyObject *res;
ret = flush_accumulator(acc);
Py_CLEAR(acc->small);
if (ret) {
Py_CLEAR(acc->large);
return NULL;
}
res = acc->large;
acc->large = NULL;
return res;
}
static void
destroy_accumulator(accumulator *acc)
{
Py_CLEAR(acc->small);
Py_CLEAR(acc->large);
}
/* Forward decls */
static PyObject *
ascii_escape_unicode(PyObject *pystr);
static PyObject *
@ -101,11 +216,11 @@ encoder_dealloc(PyObject *self);
static int
encoder_clear(PyObject *self);
static int
encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ssize_t indent_level);
encoder_listencode_list(PyEncoderObject *s, accumulator *acc, PyObject *seq, Py_ssize_t indent_level);
static int
encoder_listencode_obj(PyEncoderObject *s, PyObject *rval, PyObject *obj, Py_ssize_t indent_level);
encoder_listencode_obj(PyEncoderObject *s, accumulator *acc, PyObject *obj, Py_ssize_t indent_level);
static int
encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ssize_t indent_level);
encoder_listencode_dict(PyEncoderObject *s, accumulator *acc, PyObject *dct, Py_ssize_t indent_level);
static PyObject *
_encoded_const(PyObject *obj);
static void
@ -266,19 +381,6 @@ raise_errmsg(char *msg, PyObject *s, Py_ssize_t end)
}
}
static PyObject *
join_list_unicode(PyObject *lst)
{
/* return u''.join(lst) */
static PyObject *sep = NULL;
if (sep == NULL) {
sep = PyUnicode_FromStringAndSize("", 0);
if (sep == NULL)
return NULL;
}
return PyUnicode_Join(sep, lst);
}
static PyObject *
_build_rval_index_tuple(PyObject *rval, Py_ssize_t idx) {
/* return (rval, idx) tuple, stealing reference to rval */
@ -1226,22 +1328,22 @@ encoder_call(PyObject *self, PyObject *args, PyObject *kwds)
/* Python callable interface to encode_listencode_obj */
static char *kwlist[] = {"obj", "_current_indent_level", NULL};
PyObject *obj;
PyObject *rval;
Py_ssize_t indent_level;
PyEncoderObject *s;
accumulator acc;
assert(PyEncoder_Check(self));
s = (PyEncoderObject *)self;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "OO&:_iterencode", kwlist,
&obj, _convertPyInt_AsSsize_t, &indent_level))
return NULL;
rval = PyList_New(0);
if (rval == NULL)
if (init_accumulator(&acc))
return NULL;
if (encoder_listencode_obj(s, rval, obj, indent_level)) {
Py_DECREF(rval);
if (encoder_listencode_obj(s, &acc, obj, indent_level)) {
destroy_accumulator(&acc);
return NULL;
}
return rval;
return finish_accumulator(&acc);
}
static PyObject *
@ -1313,18 +1415,19 @@ encoder_encode_string(PyEncoderObject *s, PyObject *obj)
}
static int
_steal_list_append(PyObject *lst, PyObject *stolen)
_steal_accumulate(accumulator *acc, PyObject *stolen)
{
/* Append stolen and then decrement its reference count */
int rval = PyList_Append(lst, stolen);
int rval = accumulate_unicode(acc, stolen);
Py_DECREF(stolen);
return rval;
}
static int
encoder_listencode_obj(PyEncoderObject *s, PyObject *rval, PyObject *obj, Py_ssize_t indent_level)
encoder_listencode_obj(PyEncoderObject *s, accumulator *acc,
PyObject *obj, Py_ssize_t indent_level)
{
/* Encode Python object obj to a JSON term, rval is a PyList */
/* Encode Python object obj to a JSON term */
PyObject *newobj;
int rv;
@ -1332,38 +1435,38 @@ encoder_listencode_obj(PyEncoderObject *s, PyObject *rval, PyObject *obj, Py_ssi
PyObject *cstr = _encoded_const(obj);
if (cstr == NULL)
return -1;
return _steal_list_append(rval, cstr);
return _steal_accumulate(acc, cstr);
}
else if (PyUnicode_Check(obj))
{
PyObject *encoded = encoder_encode_string(s, obj);
if (encoded == NULL)
return -1;
return _steal_list_append(rval, encoded);
return _steal_accumulate(acc, encoded);
}
else if (PyLong_Check(obj)) {
PyObject *encoded = PyObject_Str(obj);
if (encoded == NULL)
return -1;
return _steal_list_append(rval, encoded);
return _steal_accumulate(acc, encoded);
}
else if (PyFloat_Check(obj)) {
PyObject *encoded = encoder_encode_float(s, obj);
if (encoded == NULL)
return -1;
return _steal_list_append(rval, encoded);
return _steal_accumulate(acc, encoded);
}
else if (PyList_Check(obj) || PyTuple_Check(obj)) {
if (Py_EnterRecursiveCall(" while encoding a JSON object"))
return -1;
rv = encoder_listencode_list(s, rval, obj, indent_level);
rv = encoder_listencode_list(s, acc, obj, indent_level);
Py_LeaveRecursiveCall();
return rv;
}
else if (PyDict_Check(obj)) {
if (Py_EnterRecursiveCall(" while encoding a JSON object"))
return -1;
rv = encoder_listencode_dict(s, rval, obj, indent_level);
rv = encoder_listencode_dict(s, acc, obj, indent_level);
Py_LeaveRecursiveCall();
return rv;
}
@ -1394,7 +1497,7 @@ encoder_listencode_obj(PyEncoderObject *s, PyObject *rval, PyObject *obj, Py_ssi
if (Py_EnterRecursiveCall(" while encoding a JSON object"))
return -1;
rv = encoder_listencode_obj(s, rval, newobj, indent_level);
rv = encoder_listencode_obj(s, acc, newobj, indent_level);
Py_LeaveRecursiveCall();
Py_DECREF(newobj);
@ -1414,9 +1517,10 @@ encoder_listencode_obj(PyEncoderObject *s, PyObject *rval, PyObject *obj, Py_ssi
}
static int
encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ssize_t indent_level)
encoder_listencode_dict(PyEncoderObject *s, accumulator *acc,
PyObject *dct, Py_ssize_t indent_level)
{
/* Encode Python dict dct a JSON term, rval is a PyList */
/* Encode Python dict dct a JSON term */
static PyObject *open_dict = NULL;
static PyObject *close_dict = NULL;
static PyObject *empty_dict = NULL;
@ -1436,7 +1540,7 @@ encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ss
return -1;
}
if (Py_SIZE(dct) == 0)
return PyList_Append(rval, empty_dict);
return accumulate_unicode(acc, empty_dict);
if (s->markers != Py_None) {
int has_key;
@ -1454,7 +1558,7 @@ encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ss
}
}
if (PyList_Append(rval, open_dict))
if (accumulate_unicode(acc, open_dict))
goto bail;
if (s->indent != Py_None) {
@ -1541,7 +1645,7 @@ encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ss
}
if (idx) {
if (PyList_Append(rval, s->item_separator))
if (accumulate_unicode(acc, s->item_separator))
goto bail;
}
@ -1549,16 +1653,16 @@ encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ss
Py_CLEAR(kstr);
if (encoded == NULL)
goto bail;
if (PyList_Append(rval, encoded)) {
if (accumulate_unicode(acc, encoded)) {
Py_DECREF(encoded);
goto bail;
}
Py_DECREF(encoded);
if (PyList_Append(rval, s->key_separator))
if (accumulate_unicode(acc, s->key_separator))
goto bail;
value = PyTuple_GET_ITEM(item, 1);
if (encoder_listencode_obj(s, rval, value, indent_level))
if (encoder_listencode_obj(s, acc, value, indent_level))
goto bail;
idx += 1;
Py_DECREF(item);
@ -1578,7 +1682,7 @@ encoder_listencode_dict(PyEncoderObject *s, PyObject *rval, PyObject *dct, Py_ss
yield '\n' + (' ' * (_indent * _current_indent_level))
}*/
if (PyList_Append(rval, close_dict))
if (accumulate_unicode(acc, close_dict))
goto bail;
return 0;
@ -1592,9 +1696,10 @@ bail:
static int
encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ssize_t indent_level)
encoder_listencode_list(PyEncoderObject *s, accumulator *acc,
PyObject *seq, Py_ssize_t indent_level)
{
/* Encode Python list seq to a JSON term, rval is a PyList */
/* Encode Python list seq to a JSON term */
static PyObject *open_array = NULL;
static PyObject *close_array = NULL;
static PyObject *empty_array = NULL;
@ -1618,7 +1723,7 @@ encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ss
num_items = PySequence_Fast_GET_SIZE(s_fast);
if (num_items == 0) {
Py_DECREF(s_fast);
return PyList_Append(rval, empty_array);
return accumulate_unicode(acc, empty_array);
}
if (s->markers != Py_None) {
@ -1638,7 +1743,7 @@ encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ss
}
seq_items = PySequence_Fast_ITEMS(s_fast);
if (PyList_Append(rval, open_array))
if (accumulate_unicode(acc, open_array))
goto bail;
if (s->indent != Py_None) {
/* TODO: DOES NOT RUN */
@ -1652,10 +1757,10 @@ encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ss
for (i = 0; i < num_items; i++) {
PyObject *obj = seq_items[i];
if (i) {
if (PyList_Append(rval, s->item_separator))
if (accumulate_unicode(acc, s->item_separator))
goto bail;
}
if (encoder_listencode_obj(s, rval, obj, indent_level))
if (encoder_listencode_obj(s, acc, obj, indent_level))
goto bail;
}
if (ident != NULL) {
@ -1670,7 +1775,7 @@ encoder_listencode_list(PyEncoderObject *s, PyObject *rval, PyObject *seq, Py_ss
yield '\n' + (' ' * (_indent * _current_indent_level))
}*/
if (PyList_Append(rval, close_array))
if (accumulate_unicode(acc, close_array))
goto bail;
Py_DECREF(s_fast);
return 0;