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gh-150191: Avoid data race in test_sni_callback_race by colesbury · Pull Request #150193 · python/cpython · GitHub

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gh-150191: Avoid data race in test_sni_callback_race #150193

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Merged
kumaraditya303 merged 2 commits into from
Jul 7, 2026
+12 −15
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gh-150191: Avoid data race in test_sni_callback_race #150193

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gh-150191: Avoid data race in test_sni_callback_race
colesbury May 21, 2026
0db8c41
Merge branch 'main' into gh-150191-fix-test-sni-callback-race
kumaraditya303 Jul 7, 2026
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27 changes: 12 additions & 15 deletions Lib/test/test_ssl.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1604,19 +1604,24 @@ def dummycallback(sock, servername, ctx, cycle=ctx):
gc.collect()
self.assertIs(wr(), None)

@unittest.skipUnless(support.Py_GIL_DISABLED,
"test is only useful if the GIL is disabled")
@threading_helper.requires_working_threading()
def test_sni_callback_race(self):
# Replacing sni_callback while handshakes are in-flight must not
# Replacing sni_callback while a handshake is in-flight must not
# crash (use-after-free on the callback in free-threaded builds).
#
# Use a single handshake thread: OpenSSL has internal data races
# on shared SSL_CTX state when multiple handshakes run
# concurrently against the same context (gh-150191). Concurrency
# on the *setter* is what exercises the fix from gh-149816, so
# multiple toggler threads race against each other and against
# the one handshake worker.
client_ctx, server_ctx, hostname = testing_context()

server_ctx.sni_callback = lambda *a: None
done = threading.Event()
deadline = time.monotonic() + 0.1

def do_handshakes():
while not done.is_set():
while time.monotonic() < deadline:

encukou May 27, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

What do you think about running a fixed number of iterations here, and when this thread setting an event when it's done?
c_in = ssl.MemoryBIO()
c_out = ssl.MemoryBIO()
s_in = ssl.MemoryBIO()
Expand All @@ -1643,19 +1648,11 @@ def do_handshakes():
c_in.write(s_out.read())

def toggle_callback():
while not done.is_set():
while time.monotonic() < deadline:
server_ctx.sni_callback = lambda *a: None
server_ctx.sni_callback = None

workers = max(4, (os.cpu_count() or 4) * 2)
threads = [threading.Thread(target=do_handshakes)
for _ in range(workers)]
threads.append(threading.Thread(target=toggle_callback))

with threading_helper.catch_threading_exception() as cm:
with threading_helper.start_threads(threads):
done.set()
self.assertIsNone(cm.exc_value)
threading_helper.run_concurrently([do_handshakes] + 4 * [toggle_callback])

def test_cert_store_stats(self):
ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
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