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Odd hang in python waiting for child; strace wakes hung process?




Dear Cygwin heros,

I've been happily using cygwin to run buildbot slaves for several
years.  However,
periodically they hang at the end of executing git.  It kind of smells like
SIGCHLD isn't delivered somehow.

I shrugged it off as 'I'm using an ancient copy of twisted, it's my fault' for a
long time, but recently updated to latest twisted, and it is still happening;
today I came in and both of my windows buildbots are hung with it.

While sniffing around at the edges of the problem, I noticed that the
hung process would resume if I simply ran strace on it and then hit ^C
to terminate strace.

Here's the output of cygcheck and strace:
http://kegel.com/linux/cyghang/
Older context at
https://github.com/buildbot/buildbot/issues/3801

I'll surely hit this problem again soon; what other info should I gather?

My next sensible step is to use an up to date version of buildbot's slave
(I'm running a very old one at the moment), but it seems kind of
fishy that strace could wake the process up.

Thanks,
Dan

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