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Date: Wed, 23 Sep 2015 08:05:04 +0000
From: Eric Wong <e@80x24.org>
To: "Lin Jen-Shin (godfat)" <godfat@godfat.org>
Cc: yahns-public@yhbt.net
Subject: Re: -1 shutdown_timeout?
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"Lin Jen-Shin (godfat)" <godfat@godfat.org> wrote:
> Hi,
> 
> I am trying to switch one application from using rainbows
> to yahns, and the application would do some long-polling.
> 
> When I ctrl+c to interrupt yahns, I would see yahns is
> trying to drop clients which still connect, with timeout
> set to 5 (from my config setting client_timeout to 5).
> 
> However, after a few seconds, there would be messages
> like this from yahns:
> 
>     dropping 0 of 1 clients for timeout=-1

-1 means gently kill off every socket that can be killed
(inside fdmap.rb __expire).

But the shutdown tries to be gentle: it merely makes the socket
unusable to the worker thread.  It has no way to interrupt a worker
thread.

> The timeout would be -1 after a few seconds, and then
> it would only stop when those clients timeout at 60 seconds
> (this is my assumption though, it would show a request was
>  around 60 seconds from CommonLogger (assumption again)
>  in the end, and yahns would quit gracefully)

So your long request taking 60s is normal/expected?  yahns
*should* be waiting that long (unless you send another SIGQUIT).

You can probably set a shutdown_timeout >= 60s to quiet down the log
messages.  It defaults to the highest client_timeout of all the apps
running.

> I looked around the code, which should be:
> 
>   def dropping(fdmap)
>     if drop_acceptors[0] || fdmap.size > 0
>       timeout = @shutdown_expire < Yahns.now ? -1 : @shutdown_timeout
>       fdmap.desperate_expire(timeout)
>       true
>     else
>       false
>     end
>   end
>
> While Yahns.now would get growing, I don't really understand why
> it's written like this? Is this intentional? If so, how could I force
> yahns shut those clients down in this case?

Rereading the code, it seems intentional and correct.  Setting the -1
timeout, means the shutdown_timeout has expired.  yahns will not raise
cross-thread exceptions or signals to interrupt apps, so I guess the use
of the word "desperate" is a misnomer.

Admittedly, the shutdown code is a bit hairy and it took me to a bit to
fix some of the race conditions back in 2013.