When I attempt to run a command that does not exist using IPC::Open3::Simple a postgres database handle in the script gets closed.

The following code reproduces the problem. There are two $ipc->run lines. Comment one or the other out to see the different behaviour. There are several $dbh->ping lines used to narrow down where the connection was being dropped. 
#! /usr/bin/perl -w

use strict;
use Data::Dumper;
use DBD::Pg;
use IPC::Open3::Simple;

$| ++;

my $DB_NAME     = 'db_name';
my $DB_USERNAME = 'db_username';
my $DB_PASSWORD = '12345678';

# log in to the database

my $dbh = DBI->connect("dbi:Pg:dbname=$DB_NAME",
                       $DB_USERNAME,
                       $DB_PASSWORD,
) or die $DBI::errstr;

$dbh->trace(0);

# now run a query to make sure the database connection works

my $sth;
unless ($sth = $dbh->prepare("select now()")) { warn "Unable to prepar
+e SQL."; }
unless ($sth->execute()) { warn "Unable to execute SQL."; }
$sth->finish;

print "ping " , __LINE__ , " " , $dbh->ping, "\n";

# now run a command that fails

my (@cmd_output, @err_output);
my $ipc = IPC::Open3::Simple->new(
      in  => sub { my $fh = shift; print $fh "mydata"; close $fh; } ,
      out => sub { push @cmd_output, $_[0]; } ,
      err => sub { push @err_output, $_[0]; } ,
);

print "ping " , __LINE__ , " " , $dbh->ping, "\n";

#$ipc->run('date');            # this line is fine
$ipc->run('no-such-command');  # this line causes the problem

print "ping " , __LINE__ , " " , $dbh->ping, "\n";

print Dumper("output:", \@cmd_output, "error:", \@err_output), "\n";

print "ping " , __LINE__ , " " , $dbh->ping, "\n";

# now run another database query
unless ($sth = $dbh->prepare("select now()")) { warn "Unable to prepar
+e SQL."; }
print "ping " , __LINE__ , " " , $dbh->ping, "\n";
unless ($sth->execute()) { warn "Unable to execute SQL."; }
print "ping " , __LINE__ , " " , $dbh->ping, "\n";
$sth->finish;

$dbh->disconnect() or die $DBI::errstr;

exit 0;

[download]
The successful run looks like: 
ping 30 1
ping 41 1
ping 46 1
$VAR1 = 'output:';
$VAR2 = [
          'Fri Apr 18 17:34:43 MDT 2008'
        ];
$VAR3 = 'error:';
$VAR4 = [];

ping 50 1
ping 54 1
ping 56 1

[download]

The failing run looks like: 
ping 30 1
ping 41 1
ping 46 0
$VAR1 = 'output:';
$VAR2 = [];
$VAR3 = 'error:';
$VAR4 = [
          'Can\'t exec "no-such-command": No such file or directory at
+ /usr/lib/perl5/5.8.8/IPC/Open3.pm line 246.',
          'open3: exec of no-such-command failed at /usr/lib/perl5/sit
+e_perl/5.8.8/IPC/Open3/Simple.pm line 61'
        ];

ping 50 0
ping 54 0
DBD::Pg::st execute failed: no connection to the server at reproduce-c
+rash.pl line 55.
Unable to execute SQL. at reproduce-crash.pl line 55.
ping 56 0

[download]

After working on it for a while I suspect the IPC::Open3::Simple code ends up doing something like the following:

* fork a child process. This process is a copy of the parent (ie it is a perl process).
* The child process tries to exec the command.
* The command does not exist so exec fails.
* The child perl process exits and closes the database handle it copied from the parent.

I am thinking of adding code to check to see that the first argument in the command to be executed is a readable, executable file.

Any other ideas of how to not have the database connection close?

Update: I should also mention there is nothing showing up in the postgres server log file (just autovacuum entries).

In reply to IPC::Open3::Simple closes database connection on error. by superfrink

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