PERL & UNIX : critical race?

[Enrico Venturi]

Hello colleagues;
please see the following branch of a PERL program:
$pid_open3 = open3($in, $out, "", "/usr/contrib/bin/gzip -c $currFile");

my $hnd = RemoteWriteFromArray($host, "${currRemoteFile}.gz", $user, $group, $mode, undef, $system, $instance, "NOBUFFER");

while (<$out>) {
print $hnd $_;
}

The expected behaviour is:
run a gzip by the open3
recevives the output of gzip by $out
write to the remote socket the output of gzip

Unfortunately sometimes it doesn't work: the gzip continues producing output but nothing is sento to the remote socket

Maybe the print fails because the $hnd isn't a valida handler anymore or something else?
maybe the gzip output isn't catched anymore by the script?

thanks
Enrico

[Elmar P. Kolkman]

Enrico, I would suggest to start testing result codes from the routines ('or die "...") to begin with. Make sure te RemoteWriteFromArray results in a valid socket. And while you're at it, also check the open3 call. You might even check the print command.

[Enrico Venturi]

The fact is that the remote write is started but it's stopped after a while ...
For instance for a file of 69478 bytes only 44563 are written .. this is almost systematic when the script runs free; it doesn't happen when I run the PERL debugger :-(

[Ralph Grothe · Accepted solution]

Hi Enrico,

could it be that your code fell victim to Unix buffering of the gzip command?

Have a look at the POD of IPC::Open3 (i.e. perldoc IPC::Open3) where this issue is mentioned.

In the perlipc POD (perldoc perlipc) position your pager's cursor to "/Unix buffering".
There you will find a hack that uses pseudo tty to overcome this.

[Enrico Venturi]

Hello,
I tried to change my code but now I get this error ....
my($out) = gensym();
$out = open_proc('/usr/contrib/bin/gzip -c $currFile');


DB<7> n
Remotizer doesn't contain an __DATA__ token at /alcatel/Kernel/lib/lib_perl/Remotizer.pm line 1440
Carp::croak('Remotizer doesn\'t contain an __DATA__ token') called at /usr/local/lib/perl5/5.00503/SelfLoader.pm line 45
SelfLoader::_load_stubs('SelfLoader', undef) called at /usr/local/lib/perl5/5.00503/SelfLoader.pm line 19
SelfLoader::AUTOLOAD('/usr/contrib/bin/gzip -c $currFile') called at /alcatel/Kernel/lib/lib_perl/Remotizer.pm line 1440
Remotizer::RemoteCopy('/tmp/y', 'h3grm2:/tmp/db.sav', 'snml', 'dba', 0777, 'compress') called at ./xxx line 83
Debugged program terminated. Use q to quit or R to restart,
use O inhibit_exit to avoid stopping after program termination,
h q, h R or h O to get additional info.
DB<7>