use strict;
use warnings;

use IO::Handle qw( );
use IO::Select qw( );

{
   pipe(my $fh_r, my $fh_w)
      or die("Unable to create pipe: $!\n");

   $fh_w->autoflush(1);

   my $sel_w = IO::Select->new($fh_w);

   {
      print("Filling up the pipe...\n");

      my $buf = 'x';

      for (;;) {
         my @ready_w = $sel_w->can_write(0.5);

         # Pipe is full!
         last if not @ready_w;

         die if @ready_w != 1;
         die if $ready_w[0] != $fh_w;

         my $rv = syswrite($fh_w, $buf, length($buf));

         if (not defined $rv) {
            die("Unable to write to the pipe: $!\n");
         }

         if (not $rv) {
            die("Unable to write to the pipe: 0 bytes written??\n");
         }
      }
   }

   {
      print("Opening up one byte in the pipe...\n");

      my $buf = '';

      my $rv = sysread($fh_r, $buf, 1);

      if (not defined $rv) {
         die("Unable to read from the pipe: $!\n");
      }

      if (not $rv) {
         die("Unable to read from the pipe: 0 bytes read??\n");
      }
   }

   {
      print("Make sure it's safe to write to the pipe...\n");

      my @ready_w = $sel_w->can_write();

      die if @ready_w != 1;
      die if $ready_w[0] != $fh_w;
   }

   {
      print("Writing more chars to the pipe than the pipe can handle...\n");

      my $buf = 'x' x (1024*1024);

      my $rv = syswrite($fh_w, $buf, length($buf));

      if (not defined $rv) {
         die("Unable to write to the pipe [2]: $!\n");
      }

      if (not $rv) {
         die("Unable to write to the pipe [2]: 0 bytes written??\n");
      }

      printf("Wrote %d bytes to the pipe\n", $rv);
   }

   close($fh_w);
   close($fh_r);
}