Re: [lwip-users] LwIP multithread select mode problems

[Jin Won Seo]

Sorry for irrelevant reply, but I am so frustrated to find a job.

I used Lwip 1.4.1 in my project + RTOS, but ... almost nothing I can find.

Is this industry dead? These skill sets are not useful?

On Thu, Jun 23, 2016 at 7:33 AM, Joel Cunningham <address@hidden> wrote:

Hi,

select() can be used by multiple threads at the same time and you can even have the same sockets in multiple calls and it will be safe.  The limitation comes from trying to use the same sockets from multiple simultaneous threads in other socket APIs (select is the exception, simultaneous send, recv, or close on the same socket is not supported, especially in 1.4.1).

In regards to the maxfd question, I think there is a small misunderstanding.  The maxfd parameter in select() is the largest FD in your input FD_SETs + 1.  This is because maxfd is used to iterate through the FD_SETs provided.  It has nothing to do with other threads calling select() or how many sockets are in the system, but the maximum value of any FDs in the current select() call.

Joel

On Jun 23, 2016, at 03:59 AM, lampo <address@hidden> wrote:

hello,
can someone help me with multithread problem ?

we use lwip 1.4.1 in PLC products, and if it live through long time(1 month
for example) testing in industry use,
I will back here to report.

*our problem*
we use multithread select mode in our system, and it "seems" it's ok till
now(1 days passed),
but I see the doc in rawapi.txt,"/Netconn or Socket Api are not reentrant at
the control bolck granularity level/" .
so I really cannot figure out if im doing right thing.

*our application background/restriction*

a, our system is RTOS based , we need 2 TCP clients(separately connecting to
2 TCP servers, i.e., 2 lasers),
1 TCP server(deal with max of 4 remote clients,i.e.,4 modbus clients ), and
1 web server.

b, lwip related thread cannot be in polling mode, for here is already a
polling thread in RTOS and it has "soft real time" requirements.

c, current lwip version is 1.4.1(we are evaluating 2.0.0)

d, we need to send data to tcp servers periodically, 10 ms

*our design/implementation *

3 thread has used 'select' , but the same socket is only closed by the
thread who created it. here is details,

we use 'select' in "user tcp client send thread" ,we first call
'connect',and then call 'select' to determine whether the socket is
connected correctly or not; if some errors detected in connecting or data
sending, we call 'close' to close the socket.
we use 'select' in "user tcp client receive thread", blocked forever
waiting for data, and call 'recvfrom' if data received, if some errors
detected
in this thread,we don't just clost the socket ,but send message to "user tcp
client send thread" and tell it to close.
we use 'select' in "user tcp server thread",listening for incoming requests,
receiving and responding(sending) data.

*our doubt*
1、 ‘select’ can be used in multithread or not? if yes, the first param
maxfdp1 of lwip_select() must be set to the total number of sockets in each
thread?
for example,in our situation, maxfdp1 = 2(clients) + 4(remote clients) +
1(listen socket) in each select?

2、is SYS_ARCH_PROTECT must be used in multithread?

3、if lwip 1.4.1 does not support the multithread select mode, does lwip
2.0.0 supports it?

Thanks a lot !



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