init_once_async_example.py

import asyncio

num_times = 0

async def one_time_setup():
	global num_times
	num_times += 1
	print("doing setup")
	await asyncio.sleep(1)


D = {}
async def maybe_initialize():
	global D
	this_setup = asyncio.ensure_future(one_time_setup())
	actual_setup = D.setdefault('initializer', this_setup)
	if this_setup is not actual_setup:
		print('canceling')
		this_setup.cancel()
	await actual_setup
	return

async def main():
	await asyncio.wait([
		maybe_initialize(),
		maybe_initialize(),
		maybe_initialize(),
		maybe_initialize(),
	])
	print(f'ran {num_times} times')

asyncio.run(main())

'''
# Output
$ python3 test.py
canceling
canceling
canceling
doing setup
ran 1 times
'''