Very Computer

Hi,

I need to analyze a potrential situation and possibly change the strategy
of our application. Here is the critical part of the application which has
to do with sockets (SunOS, TCP sockets, C language and gcc complier).

When a certain test starts, a Supplier starts generating packets and writing
them to a socket. This is done in a loop, where on each iteration a packet is
written (and other, non-related things happen as well). Another part of
the system, a Consumer, reads these packets as they arrive on the socket.
This is done in a totally asyncronous mode, till the end of the test. The
problem is that sometimes the Consumer consumes the packets in a slower pace
than the Supplier generates them. Therefore there is a need to add some
"smart" logic to the Supplier, so that it will be able to detect when there
are packets still waiting to be consumed, and not generate a packet at such
time.

I did not find (or just missed) any ideas in Stevens books, or FAQ.

One direction I have at the moment is to change the write() of the
Supplier to something like (in pseudo-code):

while( not-finished-writing-whole-packet )
{
  n = write(osock, packet, size);
  if( n == size )
    finished-writing-whole-packet;
  else
  {
    decrease size by value of n;
    advance some pointer on packet;
  }

Quote:}

while( run-forever-in-this-main-loop )
{
  if( no-packets-pending-on-socket ||
      just-a-few-packets-pending-on-socket ||
      enough-space-on-the-socket-to-write-another-packet )
    generate-and-write-another-packet;

  /* continue with other events and things to do */
  ...

Quote:}

--

\_\_\_  Without action there is no change. _/_/_/

When a write to a non-blocking socket returns EWOULDBLOCK, remember
the pointer into the packet you were writing, add the socket to a
select write-set and enter select().

Select will return when the socket has become writable. In select you
can also watch for other events to happen or have a timeout.

Sami

Jeff

the solution to your problem would be like this:

#include <sys/types.h>

struct fd_set           write ;
struct timeval          TO = { 0,10 }  /* 10 us */

FD_ZERO(&write)
FD_SET(osock,&write)
try_again:
switch(select(osock+1,NULL,&write,NULL,&TO))
{
  case -1 : if (errno != EINTR) /* Ouch ! */
            else goto try_again ;
  case 0  : /* time out: 10 us */
            /* do something else */
            break ;
  default : /* avaibality to write on socket ? */
            if (FD_ISSET(osock,&write)
            {
                /* write socket */
            }

Quote:}