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This is basically the same as #26939, but rather than Android running in an emulator it is affecting Cygwin running in a slow VM (in this case it's on my university's OpenStack infrastructure--I don't know what hypervisor they're using but probably KVM--either way the point is that it's a Windows VM and relatively slow).
With Cygwin on Windows running natively this has never been a problem.
FWIW I tried my own version of Victor's patch from #23428 (adapted to the new _PyTime API). This patch would be worth applying regardless and I can attach my version of the patch to that ticket, but alone it did not fix it.
On top of that I also added a version of Xavier's patch from #26939 that adjusts the wait interval in PyCOND_TIMEDWAIT to ensure that the deadline is late enough to account for delays. I'm not sure that this is completely fool-proof, but it solved the problem for me. With that patch I was unable to make the system hang again.
For some reason in #26939 that more general fix was abandoned in favor of simply setting the switch interval less aggressively for those tests in the particular case of the android emulator. But it seems that the more general fix might still be worthwhile.