gh-150942: Speed up json.loads array and object decoding

[eendebakpt]

Benchmarks on FT build:

Benchmark	speedup vs main
array_strings	1.16×
array_ints	1.08×
config	1.07×
bm_json_loads	1.03×
geomean	1.08×

The relative performance gain is larger with #150639 included (geomean 1.12x)

Benchmark script

"""Compare json.loads across four shapes: bm_json_loads, config, int array, string array."""
import json
import random
import sys
import pyperf

# --- bm_json_loads (pyperformance) documents ---
DICT = {'ads_flags': 0, 'age': 18, 'bulletin_count': 0, 'comment_count': 0,
        'country': 'BR', 'encrypted_id': 'G9urXXAJwjE', 'favorite_count': 9,
        'first_name': '', 'flags': 412317970704, 'friend_count': 0, 'gender': 'm',
        'gender_for_display': 'Male', 'id': 302935349, 'is_custom_profile_icon': 0,
        'last_name': '', 'locale_preference': 'pt_BR', 'member': 0,
        'tags': ['a', 'b', 'c', 'd', 'e', 'f', 'g'], 'profile_foo_id': 827119638,
        'secure_encrypted_id': 'Z_xxx2dYx3t4YAdnmfgyKw', 'session_number': 2,
        'signup_id': '201-19225-223', 'status': 'A', 'theme': 1,
        'time_created': 1225237014, 'time_updated': 1233134493,
        'unread_message_count': 0, 'user_group': '0', 'username': 'collinwinter',
        'play_count': 9, 'view_count': 7, 'zip': ''}
TUPLE = ([265867233, 265868503, 265252341, 265243910, 265879514, 266219766,
          266021701, 265843726, 265592821, 265246784, 265853180, 45526486,
          265463699, 265848143, 265863062, 265392591, 265877490, 265823665,
          265828884, 265753032], 60)


def _mutate(o, r):
    d = dict(o)
    for k, v in d.items():
        rv = r.random() * sys.maxsize
        if isinstance(k, (int, bytes, str)):
            d[k] = type(k)(rv)
    return d


_r = random.Random(5)
DICT_GROUP = [_mutate(DICT, _r) for _ in range(3)]
BM_OBJS = (json.dumps(DICT), json.dumps(TUPLE), json.dumps(DICT_GROUP))


def bm_json_loads(objs):
    for obj in objs:
        for _ in range(20):
            json.loads(obj)


# --- config.json shape (objects + small int arrays) ---
CONFIG = json.dumps({f"section_{i}": {"enabled": True, "values": list(range(50)),
                     "meta": {"name": f"s{i}", "desc": "x" * 40}} for i in range(3000)})
# --- array of ints ---
INTS = json.dumps([i for i in range(100000)])
# --- array of small strings ---
STRS = json.dumps([f"item_{i}" for i in range(100000)])

if __name__ == "__main__":
    runner = pyperf.Runner()
    runner.bench_func("bm_json_loads", bm_json_loads, BM_OBJS, inner_loops=20)
    runner.bench_func("config", json.loads, CONFIG)
    runner.bench_func("array_ints", json.loads, INTS)
    runner.bench_func("array_strings", json.loads, STRS)

• Issue: Improve performance by using reference stealing methods #150942

[sergey-miryanov]

LGTM