Re: [PATCH] attempt connects in parallel for IPv6-capable builds

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Am 29.01.2016 um 02:41 schrieb Eric Wong:
Junio C Hamano <gitster@xxxxxxxxx> wrote:
Eric Wong <normalperson@xxxxxxxx> writes:

getaddrinfo() may return multiple addresses, not all of which
are equally performant.  In some cases, a user behind a non-IPv6
capable network may get an IPv6 address which stalls connect().
Instead of waiting synchronously for a connect() to timeout, use
non-blocking connect() in parallel and take the first successful
connection.

This may increase network traffic and server load slightly, but
makes the worst-case user experience more bearable when one
lacks permissions to edit /etc/gai.conf to favor IPv4 addresses.

Umm.  I am not sure what to think about this change--I generally do
not like a selfish "I'll try to use whatever resource given to me
to make my process go faster, screw the rest of the world" approach
and I cannot decide if this falls into that category.

I'll wait for opinions from others.

No problem, I can also make it cheaper for servers to handle
aborted connections in git-daemon:

standalone:

   1) use recv with MSG_PEEK or FIONREAD to determine if there's
      readable data in the socket before forking (and avoid
      forking for zero-bytes-written connections)

   2) use TCP_DEFER_ACCEPT in Linux and dataready filter in FreeBSD
      for standalone git-daemon to delay accept()

inetd:

   3) suppress die("The remote end hung up unexpectedly")
      if no bytes are read at all

At some point in the future, I would love to have git-daemon implement
something like IDLE in IMAP (to avoid having clients poll for updates).
Perhaps the standalone changes above would make sense there, too.

Before you submit a patch in that direction (or resubmit the patch under discussion here), could you please find someone to test your patch on Windows first? A lot of the infrastructure mentioned may not be available there or may not work as expected. (I admit that I'm just hand-waving, I haven't tested your patch.)

Thanks,
-- Hannes

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