From: Eric Wong <normalperson@...>
Date: 2017-12-14T07:10:23+00:00
Subject: [ruby-core:84256] Re: [Ruby trunk Bug#14181] hangs or deadlocks from waitpid, threads, and trapping SIGCHLD

Thanks.  It seems the culprit is Timeout using Thread#join.
Our deadlock checking code might be buggy...

I write similar process management code all the time without
Timeout and never have this problem, so I'll investigate
(but no promises, it's tricky code)


Fwiw, I use waitpid(..., WNOHANG) in a loop until ECHLD, and
use select/IO#wait_*able + self-pipe to timeout).  Looping
(with WNOHANG) is important, since SIGCHLD interrupts can be
merged.

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