[lwip-users] Incoming packets not seen by lwip_select on second accept

[Ian Wilson]

Hello all,

I can provide more details than this (incl. lwip debgs and wireshark 
logs) but I wanted to find out first if there is something obvious 
before imposing on people to parse my detailed data.  I have tried to 
search for relevant Q&A's but with no success.

I have a lwip based system running on a soft-core processor.  The stack 
is based on LwIP v1.4.0 RC1 I believe.

I am using sockets and POSIX threads.

A thread (socketListenerThread) binds to and listens for connections on 
a high-numbered TCP port.  When a connection comes, it is accepted 
(lwip_accept) in a new thread (the socketHandlerThread) is created and 
the accepted socket passed in via the thread creation argument. The 
handler thread casts this arg appropriately to an int socket 
descriptor.  lwip_select, with a one second timeout, is used in a loop 
to wait for incoming packets.  On timeout, various high lever timeout 
and status values are checked to see if thread termination is needed, 
otherwise lwip_select is called again.  When the handler thread exits it 
closes the accepted socket.

If a new connection request comes in while the handler thread is 
running, the new connection is refused.  Only one connection at a time 
is allowed at this stage. (This may change in the future.)  Speed and 
throughput are not huge issues (now at least) so I am not too worried 
about static thread pools etc.

This all works for the first connection.  The problem is that incoming 
packets are not "detected" by lwip_select for subsequent connections to 
the listener (after closing the first connection of course).

I can't see a difference between the two connections and packet flow in 
wireshark or in lwip debugs - apart from there being no response from my 
high level code to the incoming packets on the second and later 
connections.  Lwip debugs show that something is being received by the 
lwip stack, but it doesn't then seem to get all the way up to trigger 
lwip_select.

Is this something obvious? If not I will provide some code and wireshark 
and lwip debug logs.

Any suggestions on the best lwip debug settings that would help detect 
where the problem is?

Sorry for imposing,
Ian