Re: [bug-gawk] Adding an API hook to enable a select extension

[Andrew J. Schorr]

Hi,

On Thu, May 30, 2013 at 09:53:32AM -0400, Andrew J. Schorr wrote:
> It would be really nice to add a "select" extension to gawk to solve
> this type of problem and enable I/O multiplexing.  I don't think the
> existing extension API provides enough features for this to be implemented.
> 
> I think we need an API hook to call the getredirect function.  Arnold, do you
> have any thoughts on this?

At the risk of making Brian Kernighan throw up, since he believes no awk
program should be longer than 2 lines, I propose the attached patch to the API.
I could be mistaken, but I think this should be enough to implement a select
extension.  If the name argument is NULL, it would return &curfile.public.
Otherwise, it would return &getredirect(name, strlen(name))->iop->public.  We
might want to replace the red_head array with a hash table to optimize the
performance of getredirect.

User code might look something like this:

@load "select"

BEGIN {
   server1 = "/inet4/tcp/0/127.0.0.1/12345"
   server2 = "/inet4/tcp/0/127.0.0.1/23451"
   delete writefds
   delete exceptfds
   timeout = 1.0        # in seconds
   while (1) {
      readfds[server1] = ""
      readfds[server2] = ""
      switch (select(readfds, writefds, exceptfds, timeout)) {
      case -1:
         printf "Error: select failed: %s\n", ERRNO > "/dev/stderr"
         exit 1
      case 0:
         print "Timeout.  Trying again."
         break
      default:
         for (i in readfds) {
            if ((i |& getline) > 0)
               print "Received from %s:", i, $0
            else {
               printf "I/O error from %s: %s\n", i, ERRNO > "/dev/stderr"
               exit 1
            }
         }
         break
      }
   }
}

Thoughts?

Regards,
Andy

gawkapi.patch
Description: Text document