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bpo-31882: Cygwin: fix/skip some tests to work around hang in asyncio/asyncore test suites #4149

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bpo-31882: Cygwin: fix/skip some tests to work around hang in asyncio/asyncore test suites #4149

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embray
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@embray embray commented Oct 27, 2017 •
edited by bedevere-bot
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From the issue:

Some of the tests for asyncio and asyncore block forever on Cygwin, due to a known (and seemingly difficult to fix) bug in Cygwin involving SO_PEERCRED on UNIX sockets.

SO_PEERCRED is a socket option that can be used to exchange file ownership info of the socket at the time the connection was established (specifically on UNIX sockets). This feature is technically supported on Cygwin, but the effect of the bug is that if two sockets are opened on the same process (even without using socketpair()), the credential exchange protocol can cause connect() on the "client" socket to block unless the "server" socket is already listen()-ing.

This situation is not all that common in practice (it is not a problem if the "client" and "server" are separate processes). But it does show up in the test suite in a number of places, since both sockets belong to the same process.

This PR fixes the issue in some cases by explicitly NULL-ifying the SO_PEERCRED struct on the socket. This is preferable because with this small workaround those tests pass. Unfortunately, in other cases it was difficult to do this just for the test suite without too much meddling, so I just marked those tests to be skipped.

https://bugs.python.org/issue31882

@embray embray requested a review from 1st1 as a code owner October 27, 2017 13:12
embray added 2 commits December 7, 2017 11:57
@embray
Fix tests in test_asyncore that are affected by a bug in Cygwin:
c2fd5de 
* connect()-ing an AF_UNIX socket can hang indefinitely
  if the server is not actively accept()-ing connections; see
  https://cygwin.com/ml/cygwin/2017-01/msg00054.html This issue is
  worked around explicitly in the tests, but not generally in asyncore
  (as the only known general workaround breaks SO_PEERCRED queries).
  It's also something of a corner-case which won't affect non-test code
  often.
@embray
Several other tests that are affected by the Cygwin SO_PEERCRED bug.
d24bdb9 
Unfortunately it's harder to work around in these tests since socket creation
is significantly more buried in the code being tested.  Better to just skip
them.
@iritkatriel
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iritkatriel commented Oct 20, 2021 •
edited by bedevere-bot
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The bpo was closed under bpo-45537 (Cygwin is unsupported).

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@embray @iritkatriel @the-knights-who-say-ni @bedevere-bot