Re: Testing with concurrent sessions

On Jan 6, 2010, at 6:31 PM, Kevin Grittner wrote:

> As far as I've been able to determine so far, to call psql in a
> relatively portable way would require something like this:
>
> http://perldoc.perl.org/perlfork.html

Here's an example using IPC::Open3:

#!/usr/local/bin/perl -w

use strict;
use warnings;

use IPC::Open3;
use Symbol 'gensym';
use constant EOC => "__DONE__\n";

my ($in1, $out1, $err1) = (gensym, gensym, gensym);
my ($in2, $out2, $err2) = (gensym, gensym, gensym);

my $pid1 = open3 $in1, $out1, $err1, 'bash';
my $pid2 = open3 $in2, $out2, $err2, 'bash';

print $in1 "cd ~/dev/postgresql\n";
print $in1 "ls doc\n";
print $in1 "echo ", EOC;
while ((my $line = <$out1>)) {
last if $line eq EOC;
print "LS: $line";
}

print "#### Finished file listing\n\n";

print $in2 "cd ~/dev/postgresql\n";
print $in2 "head -4 README\n";
print $in2 "echo ", EOC;
while (defined( my $line = <$out2> )) {
last if $line eq EOC;
print "HEAD: $line";
}

print "#### Finished reading README\n\n";

print $in1 "exit\n";
print $in2 "exit\n";
waitpid $pid2, 0;

print "#### All done!\n";

With that, I get:

LS: KNOWN_BUGS
LS: MISSING_FEATURES
LS: Makefile
LS: README.mb.big5
LS: README.mb.jp
LS: TODO
LS: bug.template
LS: src
#### Finished file listing

HEAD: PostgreSQL Database Management System
HEAD: =====================================
HEAD:
HEAD: This directory contains the source code distribution of the PostgreSQL
#### Finished reading README

#### All done!

I could easily write a very simple module to abstract all that stuff for you, then you could just do something like:

my $psql1 = Shell::Pipe->new(qw(psql -U postgres));
my $psql2 = Shell::Pipe->new(qw(psql -U postgres));

$psql1->print('SELECT * from pg_class');
while (my $line = $psql1->readln) { print "Output: $line\n" }
$psql1->close;

All I'd need is some more reliable way than "echo "DONE__\n" to be able to tell when a particular command has finished outputting.

Thoughts?

Best,

David