writing to and reading from fifo

diomedea has asked for the wisdom of the Perl Monks concerning the following question:

Dear Perl monks, i am trying to write the results of some parsing to a fifo to be read by the oracle sqlloader, all in the same perl script but i cant make it work without blocking.. heres the code:

if ($pid = open ($fifo, "|-")) # cookbok 16.11 open for r and w to ava
+oid blocks
{
   $fifo->autoflush(1);

     no warnings;
     foreach my $ky (sort keys %categories)
     {
        print $fifo "$categories{$ky}#";
     }

    close $fifo
        or die $! ? "Syserr closing fifo writer: $!"
                  : "Wait status $? from fifo writer";
}
else # child
{
   die "Cannot fork: $!" unless defined $pid;
 
    # copy from parent (now stdin) into the file # need to redirect st
+din?

 #$fifofile->autoflush(1);
 
    while (<STDIN>)
    {
        $fifofile = $_;
      # print  $fifofile;
      system "sqlldr control=atpctl.ctl data=atp_fifo.dat userid=someu
+ser/pwd log=loader.log";
  
    }
    exit;       # Don't forget to make the fifo disappear.
}
[download]

I can get the writer to print the line to stdout but sqlloader just hangs. im not wedded to this approach if it looks like a bad thing to do, but i have to parse 1000 files and read them in, so id rather do it in memory. thanks

Comment on writing to and reading from fifo Download Code

Replies are listed 'Best First'.
Re: writing to and reading from fifo by Anno (Deacon) on Mar 26, 2007 at 09:51 UTC
Two things make me wonder. You write I can get the writer to print the line to stdout but sqlloader just hangs. Your code `print $fifo "$categories{$ky}#";` [download] doesn't print lines (unless there are line feeds embedded in `$categories{$ky}`), but you are using line oriented `<STDIN>` to read the data. That may lead to unexpected blocking. Second, as far as I understand `sqlldr`, your command `"sqlldr control=atpctl.ctl data=atp_fifo.dat userid=someu +ser/pwd log=loader.log"` [download] will try to read data from the disk file "`atp_fifo.dat`". I don't see how that file is connected to the pipe output. Anno	[reply] [d/l] [select]
Re^2: writing to and reading from fifo by f00li5h (Chaplain) on Mar 26, 2007 at 10:15 UTC
++Anno does speak wisdom on this subject. All the binaries in `$ORACLE_HOME/bin` (that I used, with Oracle 10G) refused to read/write STDIN/STDOUT they would tend to take their configuration from files on the disk... I ended up generating the config files with templates, and writing them in /tmp with a unique filename. I wish I'd used File::Temp `@_=qw; ask f00li5h to appear and remain for a moment of pretend better than a lifetime;;s;;@_[map hex,split'',B204316D8C2A4516DE];;y/05/os/&print;`	[reply] [d/l] [select]
Re^3: writing to and reading from fifo by diomedea (Sexton) on Mar 26, 2007 at 11:10 UTC
yes this approach does work but I cant understand why i cant read the named pipe to sqlldr from within the program.. iam sure something is blocking somewhere ... back to the manuals i guess ;+)	[reply]
Re^4: writing to and reading from fifo by Anno (Deacon) on Mar 26, 2007 at 12:58 UTC