The select function is not particularly efficient when dealing with a
large number of sockets. The application has to build a big set of
bits and pass it in. RTEMS has to look through all those bits and see
what is ready. Then the application has to look through all the bits
again.
On the other hand, when using RTEMS, the select function is needed
exactly when you have a large number of sockets, because that is when
it becomes prohibitive to use a separate thread for each socket.
I think it would make more sense for RTEMS to support callback
functions which could be invoked when there is data available to read
from a socket, or when there is space available to write to a socket.
Accordingly, I implemented them.
This patch adds two new SOL_SOCKET options to setsockopt and
getsockopt: SO_SNDWAKEUP and SO_RCVWAKEUP. They take arguments of
type struct sockwakeup:
struct sockwakeup {
void (*sw_pfn) __P((struct socket *, caddr_t));
caddr_t sw_arg;
};
They are used to add or remove a function which will be called when
something happens for the socket. Getting a callback doesn't imply
that a read or write will succeed, but it does imply that it is worth
trying.
This adds functionality to RTEMS which is somewhat like interrupt
driven socket I/O on Unix.
After the patch to RTEMS, I have appended a patch to
netdemos-19990407/select/test.c to test the new functionality and
demonstrate one way it might be used. To run the new test instead of
the select test, change doSocket to call echoServer2 instead of
echoServer.
