path/to/venv/lib/python3.10/site-packages/gradio/wasm_utils.py

from __future__ import annotations

import sys
from contextlib import contextmanager
from contextvars import ContextVar

# See https://pyodide.org/en/stable/usage/faq.html#how-to-detect-that-code-is-run-with-pyodide
IS_WASM = sys.platform == "emscripten"


class WasmUnsupportedError(Exception):
    pass


# Mapping from app ID to the Gradio's FastAPI app instance (`app`).
# To support the SharedWorker mode where multiple apps are running in the same worker,
# we need to keep track of the app instances for each app ID.
app_map = {}


# `with app_id_context(app_id):` is used to set the app ID
# which `register_app()` uses to register the app instance.
# Context variables are natively supported in asyncio and
# can manage data in each task (https://docs.python.org/3/library/contextvars.html#asyncio-support),
# so we can use them for this purpose.
_app_id_context_var: ContextVar[str | None] = ContextVar("app_id", default=None)


@contextmanager
def app_id_context(app_id: str):
    token = _app_id_context_var.set(app_id)
    yield
    _app_id_context_var.reset(token)


# `register_app` and `get_registered_app` are used
# for the Wasm worker to get a reference to
# the Gradio's FastAPI app instance (`app`).
def register_app(_app):
    app_id = _app_id_context_var.get()

    if app_id in app_map:
        app = app_map[app_id]
        app.blocks.close()

    app_map[app_id] = _app


class GradioAppNotFoundError(Exception):
    pass


def get_registered_app(app_id: str):
    try:
        return app_map[app_id]
    except KeyError as e:
        raise GradioAppNotFoundError(
            f"Gradio app not found (ID: {app_id}). Forgot to call demo.launch()?"
        ) from e