middleware: reuse inet_diag netlink socket

middleware: reuse inet_diag netlink socket

Eric Wong <bofh@yhbt.net> wrote:
> I'll squash this in for fork+preload safety.

I forget there are multithreaded servers using this :x

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Subject: [PATCH v3] middleware: reuse inet_diag netlink socket

No point in constantly allocating and deallocating FDs (and Ruby
IO objects) when reusing them is supported.

However, we must guard it against parallel callers since
linux_inet_diag.c::diag releases the GVL while calling
sendmsg(2) and recvmsg(2), so it's possible two Ruby threads can
end up crossing streams if the middlware is used with a
multi-threaded server.

AFAIK, Raindrops::Middleware isn't a heavily-trafficked endpoint,
so saving FDs and avoiding thread specific data is preferable
for memory-constrained systems I use.