Re: TLI t_snd hangs
From: Barry Margolin (barmar_at_alum.mit.edu)
Date: 05/28/04
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Date: Thu, 27 May 2004 18:23:30 -0400
In article <2d544c6b.0405271155.42e4b153@posting.google.com>,
rybak@caseta.com (Rybak) wrote:
> Hello all,
>
> I have been searching all over the net for a solution to a problem I
> am having with an synchronous t_snd call. The setup of the system(s)
> are as follows:
>
> 1. Machine A is sending a large amount of data to Machine B
> 2. Machine A is running lynxOS 3.0.1 and B is running SunOS 5.6
>
> Both machines are using libnsl interface to TLI to communicate over
> TCP/IP.
>
> The blocking t_snd occurs about 20 seconds after the network cable has
> been removed. Durring those 20 seconds I observe that Machine A's
> mbufs are growing very quickly. It is the case that my system waits 25
> seconds before it checks the status of the network connection. So what
> happens here is the send thread gets blocked on t_snd and the system
> is frozen.
>
> Question 1. How can I check the real-time status of the transport
> endpoint on Machine A. I have tried polling, using t_look and t_sync.
> None of those functions have been able to realize that the network has
> been disconnected.
The TCP protocol doesn't support this. It tries to be fault-tolerant,
and when the cable is reconnected it will resume where it left off.
Eventually it will time out waiting for acknowledgements and report an
error to the caller; this typically takes a couple of minutes. This is
intentional -- you don't want network connections failing due to
temporary network glitches (like a network administrator doing some
recabling).
If your application needs better tracking, it should implement this in
the application protocol. Require each system to send something every
few seconds, and if you don't receive it you kill the connection.
-- Barry Margolin, barmar@alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me ***
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