from aiohttp import web

def sync_fn(param1, param2):
    time.sleep(5)
    return 'Hello, world!'

async def hello(request):
    with ThreadPoolExecutor(max_workers=1) as executor:
        future = executor.submit(sync_fn, param1, param2)
        result = future.result()
    return web.Response(text=result)

app = web.Application()
app.router.add_route('GET', '/', hello)

web.run_app(app)