[lwip-users] lwip_close blocks on non-blocking socket when cable is removed

[Fabian Koch]

Hey everyone,

 

I’m using LwIP 1.4.1 and we noticed that on a non-blocking socket, lwip_close() suddenly starts being blocking when the cable is removed.

 

This is because:

lwip_close() -> netconn_delete() -> API_MSG -> do_delconn() -> do_close_internal() -> tcp_close() -> tcp_close_shutdown() -> tcp_send_fin() -> tcp_enqueue_flags()

 

That last function checks the TCP send queue and returns with ERR_MEM when the cable is unplugged because the send queue is full.

Thus, that error is given up to do_close_internal() which does NOT sys_sem_signal() the op_completed semaphore and in turn, the API_MSG is still being waited on.

Do_close_internal() sets poll_tcp and sent_tcp callbacks which re-call do_close_interal() until it works (when the cable is re-plugged and the send queue can be worked on).

 

Is this bug known and maybe even fixed on current master branch?

We need the non-blocking sockets to actually _be_ non-blocking.

 

Kind regards,

Fabian