lkml.org 
[lkml]   [2014]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: recvmmsg() timeout behavior strangeness [RESEND]
On Sat, May 3, 2014 at 1:29 PM, Florian Westphal <fw@strlen.de> wrote:
> Michael Kerrisk (man-pages) <mtk.manpages@gmail.com> wrote:
>> Reinvestigating the problem, I see that I got my description of the
>> behavior slightly wrong, although the fundamental problem remains.
>> Here's my improved formulation:
> [..]
>
>> Since the timeout is only checked after the arrival of each datagram,
>> we can have scenarios like the following:
>>
>> 0. Assume a timeout of 10 (T) seconds, that vlen is 5, and the call
>> is made at time X
>>
>> 1. First datagram arrives at time X+2.
>>
>> 2. Second datagram arrives at time X+4 secs
>>
>> 3. Third datagram arrives at time X+6 secs
>>
>> 4. No more datagrams arrive.
>>
>> In this case, the call blocks forever. It hardly seems that this could
>> be intended behavior. The problem, of course is that the timeout is
>> checked only after receipt of a datagram.
>
> Isn't that what MSG_WAITFORONE is supposed to solve?

I don't think so. I understand the idea of the timeout to be: get as
many datagrams as you can within a certain interval. MSG_WAITFORONE is
orthogonal to that goal (you can specify MSG_WAITFORONE without an
infiniite timeout, for example).

Also, consider the algorithm above: if no datagrams arrive, the
timeout is in effect ignored.

Thanks,

Michael

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/


\
 
 \ /
  Last update: 2014-05-03 14:21    [W:0.091 / U:0.216 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site