Avoid TSan reported race in `run_udp_echo_server`

[colesbury]

The test_asyncio.test_sock_lowlevel.py test uses a UDP echo server:

cpython/Lib/test/test_asyncio/utils.py

Lines 288 to 310 in a15fede

	def echo_datagrams(sock):
	while True:
	data, addr = sock.recvfrom(4096)
	if data == b'STOP':
	sock.close()
	break
	else:
	sock.sendto(data, addr)
	@contextlib.contextmanager
	def run_udp_echo_server(*, host='127.0.0.1', port=0):
	addr_info = socket.getaddrinfo(host, port, type=socket.SOCK_DGRAM)
	family, type, proto, _, sockaddr = addr_info[0]
	sock = socket.socket(family, type, proto)
	sock.bind((host, port))
	thread = threading.Thread(target=lambda: echo_datagrams(sock))
	thread.start()
	try:
	yield sock.getsockname()
	finally:
	sock.sendto(b'STOP', sock.getsockname())
	thread.join()

Thread sanitizer complains about the sock.sendto(b'STOP', sock.getsockname()) line in the main thread happening concurrently with the sock.close() in the echo_datagrams thread.

This seems a bit bogus to me: the sendto has to start before the close starts because it triggers the echo_datagrams shutdown, but it's easy enough to avoid the data race. I also think it's better in this case to do a small code change to the test, instead of adding or keeping a global suppression.

Linked PRs

• gh-122187: Avoid TSan reported race in run_udp_echo_server #122189
• [3.13] gh-122187: Avoid TSan reported race in run_udp_echo_server (GH-122189) #122263