Segmentation fault on 0.31.0 when inside a Temporal activity

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@fantix is already working on this.

Since Dec 6, 2025.

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Description

I'm not sure if the root cause is with asyncpg or with temporal but this code works fine on 0.30.0, and crashes on 0.31.0 in await asyncpg.connect. Python 3.12.9.

#!/usr/bin/env python
import asyncio
import threading
from datetime import datetime, timedelta

import asyncpg
from temporalio import activity, workflow
from temporalio.client import Client
from temporalio.worker import Worker

TASK_QUEUE = "asyncpg-temporal-test"


async def db_call(label: str) -> None:
    """Connect to Postgres and close."""
    loop = asyncio.get_running_loop()
    print(f"[{label}] thread={threading.get_ident()} loop_id={id(loop)} {loop!r}")

    conn = await asyncpg.connect(
        host="localhost",
        port=5432,
        database="database",
        user="andrei",
    )

    print(f"[{label}] connected to Postgres")

    await conn.close()


@activity.defn
async def db_activity() -> None:
    return await db_call("activity")


@workflow.defn
class TestWorkflow:
    @workflow.run
    async def run(self) -> None:
        print("[workflow] starting db_activity")
        return await workflow.execute_activity(
            db_activity,
            start_to_close_timeout=timedelta(seconds=30),
            task_queue=TASK_QUEUE,
        )


async def main() -> None:
    # 1) Baseline: asyncpg on a fresh loop, no Temporal
    print("=== 1) Direct asyncpg on fresh loop (no Temporal) ===")
    await db_call("direct")

    # 2) Bring up Temporal client + worker and run a workflow that calls db_activity
    print("\n=== 2) Temporal worker + workflow calling async activity ===")
    client = await Client.connect("localhost:7233")
    worker = Worker(
        client,
        task_queue=TASK_QUEUE,
        workflows=[TestWorkflow],
        activities=[db_activity],
    )

    async with worker:
        # This executes TestWorkflow.run, which in turn executes db_activity
        result = await client.execute_workflow(
            TestWorkflow.run,
            id=datetime.now().isoformat(),
            task_queue=TASK_QUEUE,
        )
        print(f"[main] workflow result: {result}")


if __name__ == "__main__":
    asyncio.run(main())

Repro steps:

  1. Start a temporal server: temporal server start-dev
  2. In a separate terminal, run the code above:
% python test_asyncpg.py               

=== 1) Direct asyncpg on fresh loop (no Temporal) ===
[direct] thread=8654430720 loop_id=4353195520 <_UnixSelectorEventLoop running=True closed=False debug=False>
[direct] connected to Postgres

=== 2) Temporal worker + workflow calling async activity ===
[workflow] starting db_activity
[activity] thread=8654430720 loop_id=4353195520 <_UnixSelectorEventLoop running=True closed=False debug=False>
zsh: segmentation fault  python test_asyncpg.py
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