ContextVar cannot be updated in the handle

[scorpiord]

When I use browser-use and bubus in the fastAPI application, ContextVar cannot be updated in the handle

test code:

import asyncio
from contextvars import ContextVar

from pydantic import BaseModel


class User(BaseModel):
    userid: int
    name: str
    user_code: str


user_ctx: ContextVar[User] = ContextVar('user_ctx', default=None)
user_ctx1: ContextVar[User] = ContextVar('user_ctx1', default=None)

class CtxEvent(BaseEvent):
    ctx: Any


class MyShow:

    def __init__(self):
        self.user_event_bus = EventBus(name=f"UserAgent")
        self.user_event_bus.on(CtxEvent, self.test_show)

    async def test_show(self, event: CtxEvent):
        print(f"test_show:{id(asyncio.get_running_loop())}")
        print(event.event_id)
        user = user_ctx.get()
        print(user)
        user1 = user_ctx1.get()
        print(user1)
        print(event.ctx.get(user_ctx))
        print(event.ctx.get(user_ctx1))

    async def test_show_1(self):
        print(f"test_show_1:{id(asyncio.get_running_loop())}")
        id(asyncio.get_running_loop())
        user = user_ctx.get()
        print(user)
        user1 = user_ctx1.get()
        print(user1)

my_show_instance = MyShow()


@system_router.get("/test")
async def test(user_code,user_code1):
    user_ctx.set(User(user_code=user_code,userid=1,name="user"))
    await asyncio.create_task(test1(user_code,user_code1))

async def test1(user_code,user_code1):

    user_ctx1.set(User(user_code=user_code1,userid=1,name="user"))

    my_show_instance.user_event_bus.dispatch(CtxEvent(ctx=contextvars.copy_context()))
    # await my_show_instance.test_show_1()

Can we support switching the execution context to the dispatch event’s context when handle runs?

For example, have base_event support accepting a context, and then use the provided context when executing handle.

ctx = getattr(event, "ctx", None)

if inspect.iscoroutinefunction(handler):
    if ctx:
        handler_task = ctx.run(asyncio.create_task(handler(event)))
    else:
        handler_task = asyncio.create_task(handler(event))

    result_value: Any = await asyncio.wait_for(handler_task, timeout=event_result.timeout)

elif inspect.isfunction(handler) or inspect.ismethod(handler):
    if ctx:
        result_value: Any = ctx.run(handler, event)
    else:
        result_value: Any = handler(event)

[pirate]

My intuition is that the contexts would need to be nested or merged somehow, not just overridden because the whole point of our internal use of ContextVars is that events emitted inside handlers need to know their parent. Do you know if ctx.run() auto-stacks/nests/merges contexts?

---

P.S. FYI I am no longer working at browser-use, but I forked bubus and am maintaining it + adding new features over here now:

https://github.com/pirate/bubus

[scorpiord]

My intuition is that the contexts would need to be nested or merged somehow, not just overridden because the whole point of our internal use of ContextVars is that events emitted inside handlers need to know their parent. Do you know if ctx.run() auto-stacks/nests/merges contexts?

P.S. FYI I am no longer working at browser-use, but I forked bubus and am maintaining it + adding new features over here now:

https://github.com/pirate/bubus

Thank you for your reply.

I believe ctx.run() is meant to execute the specified method within the given contexts (ctx). When a user includes a context in an event, it indicates that they expect the corresponding handler to run within that specific context.

P.S.:
Will the bubus used by browser-use be the version that you continue to maintain (https://github.com/pirate/bubus)?

[pirate]

I've just fixed this issue in my fork in v1.7.1 (see commits 2db5914 and 1ca9709). ContextVars are now copied and stored at dispatch time and propagate to the handler correctly. To avoid memory leaks/stale db sessions lingering the context copy is deleted after all the event handlers finish executing.

As for whether browser-use will update to use my fork, unfortunately I don't have an answer at the moment. I'm still trying to figure out the best approach going forward with them so I can keep pushing fixes as an outside contributor.

For now if you need my fixes maybe you can try:

uv pip uninstall bubus
uv pip install git+https://github.com/pirate/bubus@1.7.1