App lifespan (startup/shutdown)

Run code when the app starts and stops. Used to init the DB and seed data.

Code example

@asynccontextmanager
async def lifespan(app: FastAPI):
    init_db()          # startup
    seed_database()
    yield              # app runs here
    # cleanup on shutdown

app = FastAPI(lifespan=lifespan)

How it works

The lifespan context manager wraps the app's entire run. Code before `yield` runs at startup; code after `yield` runs at shutdown. OpenBenchML uses it to create database tables (init_db) and seed default datasets on boot, and to close all WebSocket connections on shutdown. This replaced the older @app.on_event('startup') decorator and is the recommended pattern for FastAPI 0.93+.