linux-kernel - Re: epoll behaviour after running out of descriptors

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Message-ID: <b2cc26e40811021115h1bf711c7i2b220a92f7cf1abc@mail.gmail.com>
Date:	Sun, 2 Nov 2008 20:15:57 +0100
From:	"Olaf van der Spek" <olafvdspek@...il.com>
To:	"Eric Dumazet" <dada1@...mosbay.com>
Cc:	"Davide Libenzi" <davidel@...ilserver.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: epoll behaviour after running out of descriptors

On Sun, Nov 2, 2008 at 8:10 PM, Eric Dumazet <dada1@...mosbay.com> wrote:
> On listen queue, socket is still ready for an accept().

True, but not handy.

> Since you use edge trigered epoll, you'll only reveive new notification.

The strace shows I receive 10+.
If a return with EMFILE is indeed a no-op, I should receive only one.

> You probably had in you app a : listen(sock, 10), so after 10 notifications,
> your listen queue is full and TCP stack refuses to handle new connections.

I've got listen(l, SOMAXCONN);
IIRC SOMAXCONN is 128.

>  close(newfd); /* forget this incoming connection, we dont have enough fd */

Why not keep them in the queue until you do have enough descriptors?

> Of course, if your application is multi-threaded, you might adapt (and
> eventually reserve
> one emergency fd per thread)

Sounds like a great recipe for race conditions. ;)
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