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Data packets create a ctypes array type for each new payload length #911
Description
Summary
Each data packet with a new payload length creates a new ctypes array type, on the send side and on the receive side:
LocalParticipant.publish_data(participant.py#L339):cdata = (ctypes.c_byte * data_len)(*payload)Roomdata packet handler (room.py#L1118-L1121):ctypes.cast(buffer_info.data_ptr, ctypes.POINTER(ctypes.c_byte * buffer_info.data_len))
The effect depends on the Python version:
- Python 3.12 and 3.13:
ctypes.POINTER()keeps each pointer type in a cache that is never cleared, and the pointer type holds the array type. The receive side keeps one array type and one pointer type alive for each new length, for the life of the process. - Python 3.14: the types are freed, but each type is a reference cycle. Only the cyclic GC can free them, and a busy data channel gives it a lot of work.
The (*payload) unpack in publish_data also converts each byte to a Python int, the same per-byte copy that #848 reported for FfiClient.request.
Reproduction
The script connects two participants to a LiveKit server, sends 100 packets of different lengths with the GC disabled, waits until all 100 arrive, then runs gc.collect().
LIVEKIT_URL=ws://localhost:7880 LIVEKIT_API_KEY=devkey LIVEKIT_API_SECRET=secret \
uv run --no-project --python 3.12 --with livekit==1.2.0 --with livekit-api repro.py
repro.py
import asyncio, ctypes, gc, os, sys
from livekit import api, rtc
N = 100
def token(identity):
return (api.AccessToken(os.environ["LIVEKIT_API_KEY"], os.environ["LIVEKIT_API_SECRET"])
.with_identity(identity)
.with_grants(api.VideoGrants(room_join=True, room="ctypes-repro")).to_jwt())
async def main():
url = os.environ["LIVEKIT_URL"]
sender, receiver = rtc.Room(), rtc.Room()
got = []
receiver.on("data_received", lambda p: got.append(p.data))
await receiver.connect(url, token("receiver"))
await sender.connect(url, token("sender"))
while not sender.remote_participants:
await asyncio.sleep(0.1)
await sender.local_participant.publish_data(b"warmup")
while not got:
await asyncio.sleep(0.1)
got.clear()
gc.collect()
gc.disable()
for i in range(N):
await sender.local_participant.publish_data(b"x" * (1000 + i))
while len(got) < N:
await asyncio.sleep(0.1)
freed = gc.collect()
gc.enable()
lengths = range(1000, 1000 + N)
kept = [c for c in ctypes.Array.__subclasses__() if getattr(c, "_length_", None) in lengths]
print(f"livekit {rtc.__version__}, Python {sys.version.split()[0]}: "
f"freed by gc.collect(): {freed}, array types still alive: {len(kept)}")
await sender.disconnect()
await receiver.disconnect()
asyncio.run(main())| Python | livekit 1.2.0 |
|---|---|
| 3.12.12 | freed by gc.collect(): 0, array types still alive: 100 |
| 3.14.3 | freed by gc.collect(): 1300, array types still alive: 0 |
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