Udp programming question

Hi,
I have a machine that reads periodically a message on a socket.
If there've been more than one send on that address, I'd like to read
only the last arrived packet, and not the older one and so on.
How can I do to make the receive of a new packet overwrite the old
one in the kernel buffer? In the buffer should be only the last arrivad
message..

Thanks in advance
RedCrow

RedCrow wrote:
> Hi,
> I have a machine that reads periodically a message on a socket.
> If there've been more than one send on that address, I'd like to read
> only the last arrived packet, and not the older one and so on.
> How can I do to make the receive of a new packet overwrite the old
> one in the kernel buffer? In the buffer should be only the last arrivad
> message..
>
> Thanks in advance
> RedCrow


UDP packets can arrive out of order, so the "last packet sent" could
certainly be the first packet that was actually sent. If you want to
make sure they are ordered, then don't use UDP or plug some sort of
timestamp or serial number into your data that can be used by your
server/client to keep track of it.

The kernel is simply going to throw the data your way; which is exactly
what you want it to do.


--

WWJD? JWRTFM
Rot13 for email address: yvfgf @ ehqa.pbz

> UDP packets can arrive out of order, so the "last packet sent" could
> certainly be the first packet that was actually sent. If you want to
> make sure they are ordered, then don't use UDP or plug some sort of
> timestamp or serial number into your data that can be used by your
> server/client to keep track of it.
>

It is exactly what I've done. I made a timestamp to see if i read an out
of order packet.
But happens this thing: if a send is delayed beyond the period, the
receive fails, and my buffer contains the old packet. It assumes that the
packet didn't arrive. When, in the next period, I go to read the packet,
I'd like to read the one relative to that period, not the older one. One
delay in the send makes the queue of messages shifted by one, so in every
period i read the message of the previous period. I thought that this was
avoidable simply making the kernel buffer contain only one packet, and
making a new arrive delete the old content of the buffer...

Any suggestions?

RedCrow wrote:

> It is exactly what I've done. I made a timestamp to see if i read an out
> of order packet.
> But happens this thing: if a send is delayed beyond the period, the
> receive fails, and my buffer contains the old packet. It assumes that the
> packet didn't arrive. When, in the next period, I go to read the packet,
> I'd like to read the one relative to that period, not the older one. One
> delay in the send makes the queue of messages shifted by one, so in every
> period i read the message of the previous period. I thought that this was
> avoidable simply making the kernel buffer contain only one packet, and
> making a new arrive delete the old content of the buffer...
>
> Any suggestions?
>


Have you thought about flushing the buffer after you've dealt with the
data? No data, no action required.

--

WWJD? JWRTFM
Rot13 for email address: yvfgf @ ehqa.pbz