[lwip-devel] [task #6683] Document lwIPs thread safety requirements

[Frédéric Bernon]

Follow-up Comment #1, task #6683 (project lwip):

I'm ok and have start to study several points. First, I think we have to
define what in lwIP have to be thread safe. I think that we can tell that :

- lwIP core isn't thread safe. If we have to use lwIP in a multithread
environment, we should (or HAVE TO) use "upper" layers (netconn or sockets).
raw api's need to protect themselft the core.

- some upper operations have to be handled directly by application: socket,
bind, connect, setsockopt and close. I don't think it's the lwIP role to
handle that (by example, it will be difficult to know if a "int socket" is
always same between close/socket calls:

T1
   int s1=socket() (tell s1=5)
T1,T2 
   use s1 with send,recv (ok, it could be possible).
T2
   closesocket(s1)
T3
   int s2=socket() (and... it could be s2=5)
T1 
   send(s1) !!!! Problem, s1 would not the same proto/port than the first we
open, but only application can know that !!!!

- some operations can be transform to thread-safe : recv, recvfrom, send,
sendto... To enable fullduplex protocols. We have to move some processing
from netconn/sockets to api_msg, but it's possible, and even can be
faster...

- I don't use select, and I think it is a special case (lot of code is only
use for this function, and could/should be disable)...






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