Re: [msysGit] [PATCH/RFC 06/11] run-command: add kill_async() and is_async_alive()

From: Johannes Sixt <j6t@kdbg.org>
Date: Nov 27, 2009, 19:59 UTC
Message-ID: <200911272059.25934.j6t@kdbg.org>
In-Reply-To: <40aa078e0911270804i1a828ea6we1611047d37869f7@mail.gmail.com>

On Freitag, 27. November 2009, Erik Faye-Lund wrote:

> Do you really think it's better to unconditionally take down the
> entire process with an error, instead of having a relatively small
> chance of stuff blowing up without any sensible error? I'm not 100%
> convinced - but let's hope we'll find a proper fix.

"relatively small chance of stuff blowing up"? The docs of 
TerminateThread: "... the kernel32 state for the thread's process could be 
inconsistent." That's scary if we are talking about a process that should run 
for days or weeks without interruption.

The reason why we are killing a thread is to prevent keeping lots of connections open (to the same IP address). There are two situations to take care of:

1. We are in a lengthy computation without paying attention to the socket.

2. The client does not send or accept data for a long time.

Case 1 could happen if upload-pack is "counting objects" on a large repository. We would need some way to kill upload-pack. Since it is a separate process anyway, we could use TerminateProcess().

Case 2 could be achieved by using setsockopt() with SO_RCVTIMEO and SO_SNDTIMEO and a tiny timeout. But notice that we would set a timeout in one thread while another thread is waiting in ReadFile() or WriteFile(). Would that work?

-- Hannes