
7.5 years to find out how to close a file descriptor in a multithreaded process - nly
https://twitter.com/cperciva/status/1141852451756105729
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cperciva
To elaborate on this: I figured out the dup2 part of the solution a long time
ago, but I was stuck on "how do we make sure the descriptor we closed is the
one we dup2ed and not a different one"; the obvious answer of using stat only
works if you can create a sentinel file.

So really the hard part was realizing that you can use MSG_PEEK since it's
guaranteed to not have side effects (and with a random cookie can be used to
identify whether a descriptor is "our" socket).

