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

From: Andrew J. Schorr
Subject: Re: [bug-gawk] Adding an API hook to enable a select extension
Date: Thu, 30 May 2013 21:12:14 -0400
User-agent: Mutt/1.5.21 (2010-09-15)


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"

   server1 = "/inet4/tcp/0/"
   server2 = "/inet4/tcp/0/"
   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."
         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



Attachment: gawkapi.patch
Description: Text document

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