Re: strange bug with DBI, Sybase, and mod_perl

[Jonathan Swartz]

Something in which code is closing STDOUT? I know that mod_perl  
redirects STDOUT to $r->print...

Incidentally the code to reprodce for mysql is even easier - just need  
one connection. This will do it:

   use DBI;
   sub handler {
       my $dbh = DBI->connect( "DBI:mysql:$database", $user, $pass,  
{ RaiseError => 1 } );
       system(qq{perl -e 'print "abcd"'});
       eval { $dbh->do("select 1") };
       print "dbh - " . ( $@ ? "error: $@" : "ok" ) . "\n";
       return 0;
   }

And as a bonus mystery, if you only print two characters, the request  
hangs. :)

Jon

On Jan 7, 2010, at 2:03 PM, Tim Bunce wrote:

Ah. I think something in the code is closing STDOUT (fd 1) before the
handler() is called. The socket that the driver then creates to  
connect
to the server will get fd 2, aka STDOUT, and thus be inherited by the
child. Or something like that.

Tim.

On Thu, Jan 07, 2010 at 10:03:06AM -0800, Jonathan Swartz wrote:
Ok, take sendmail out of the equation. The bug will occur iff the
program sends output to STDOUT (which sendmail was doing because of
a warning).

Here's a slightly simplified version.

  our ($dbh1, $dbh2);

  sub dbconnect {
      return DBI->connect( 'DBI:Sybase:...', '...', '...', {
RaiseError => 1 } );
  }

  sub testdb {
      my ( $name, $dbh ) = @_;
      eval { $dbh->do("select 1") };
      print "$name - " . ($@ ? "error: $@" : "ok") . "\n";
  }

  sub handler {
      my ($r) = @_;

      # connect.pl contains one line: BEGIN { $Handler::dbh1 =
Handler::dbconnect() }
      do "/home/jswartz/projects/unchained-transaction/connect.pl";
      $dbh2 = dbconnect();
      system(qq{perl -e 'print "hi"'});
      testdb("dbh1", $dbh1);
      testdb("dbh2", $dbh2);

      return 0;
  }

This outputs

  dbh1 - ok
  dbh2 - error: DBD::Sybase::db do failed: OpenClient message:
LAYER = (5) ORIGIN = (3) SEVERITY = (5) NUMBER = (6)
  Server SANDBOX5, database
  Message String: ct_results(): network packet layer: internal net
library error: Net-Library operation terminated due to disco\
  nnect
  OpenClient message: LAYER = (1) ORIGIN = (1) SEVERITY = (1)
NUMBER = (50)
  Server SANDBOX5, database
  Message String: ct_cmd_drop(): user api layer: external error:
The connection has been marked dead.

However, if I replace the system with

  system(qq{perl -e ''});
or
 system(qq{perl -e 'print "hi"' > /dev/null});

then it outputs

 dbh1 - ok
 dbh2 - ok

On Jan 7, 2010, at 2:20 AM, Tim Bunce wrote:

On Wed, Jan 06, 2010 at 04:08:17PM -0800, Jonathan Swartz wrote:
Thanks for your help...this bug has me feeling very isolated...

Just about everything here is necessary to generate the bug. In
particular, I cannot generate the bug...
* If I move the code from connect.pl into the handler, even as a
string eval
* If I remove the "BEGIN" from connect.pl
* If I replace sendmail with another program

That's the most interesting one to me. Try replacing it with a  
perl
script that reports what open file descriptors have been  
inherited.

Ok. What's the easiest way to do that? :) Sorry, probably dumb
question, but never did this before and scanning perlipc and
perlopentut and google didn't yield anything obvious.

I had to rummage around a bit, but this seems to work:

 $ perl -e 'open(FH, ">&=$_") and printf "$_\n" for 0..100'
 0
 1
 2

 $ perl -e 'open(FH, ">&=$_") and printf "$_\n" for 0..100' 42<&1
 0
 1
 2
 42

(Using >&= or <&= doesn't seem to matter for this simple case.)

Tim.