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Posted to embperl@perl.apache.org by Matthew Smith <ma...@yahoo.com> on 2006/06/28 18:16:10 UTC

use of STDERR in forked children

Hi,  I'm working on a mechanism to fork a a long
running child process.  I've followed the standard
mod_perl forking wisdom in
http://modperlbook.org/html/ch10_02.html.

My issue is that warn() doesn't work in the child
process, though printing directly to STDERR does.

Also, I want STDERR to go to the apache log like it
normally would, but I don't know how to determine what
the path to the log is. I can't hard code it since it
changes depending on the environment (dev vs. qa vs.
prod).

I haven't tried this using Apache::Registry (since we
don't run it) but I thought it might be and Embperl
thing since I couldn't find anything on the mod_perl
lists...

I'm using Apache 1.3 and Embperl 1.36

Your help is greatly appreciated.

Here's the code:
[# SNIP #]
[!
    use POSIX 'setsid';
    use Apache;
!]
[-
    my $childPid = undef;
    $SIG{CHLD} = 'IGNORE';

    if ($childPid = fork) {
        $output =  "Parent $$ has finished, kid's PID:
$childPid\n";
    }
    else {
        warn "starting child $$\n";
        $req_rec->cleanup_for_exec( ); # untie the
socket
        chdir '/'                 or die "Can't chdir
to /: $!";
        open STDIN, '/dev/null'   or die "Can't read
/dev/null: $!";
        open STDOUT, '>/dev/null' or die "Can't write
to /dev/null: $!";
        open STDERR, '>>/tmp/log'  or die "Can't write
to /tmp/log: $!";
        setsid                    or die "Can't start
a new session: $!";

        my $oldfh = select STDERR;
        local $| = 1;
        select $oldfh;

        # ends up in /tmp/log
        print STDERR "Where do the children [$$]
play?\n";

        # ends up nowhere
        warn "Where do the children [$$] play?\n";

        # do something time-consuming
        for (1..20) {
            sleep 1;
            warn "$_\n";
        }
        warn "completed $$\n";

        CORE::exit(0); # terminate the process
    }
-]
[-  $dbgLogLink = 0; -]
<html><head><body>
<xmp>[+ $output +]</xmp>
</body></html>
[# ENDSNIP #]

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Re: use of STDERR in forked children

Posted by Angus Lees <gu...@inodes.org>.
On 6/28/06, Matthew Smith <ma...@yahoo.com> wrote:
>
> Hi,  I'm working on a mechanism to fork a a long
> running child process.  I've followed the standard
> mod_perl forking wisdom in
> http://modperlbook.org/html/ch10_02.html.
>
> My issue is that warn() doesn't work in the child
> process, though printing directly to STDERR does.


You probably want to reset/check $SIG{__WARN__} .

Also you probably want to reset $SIG{PIPE}, from memory.

Also, I want STDERR to go to the apache log like it
> normally would, but I don't know how to determine what
> the path to the log is. I can't hard code it since it
> changes depending on the environment (dev vs. qa vs.
> prod).


I thought STDERR in the apache process already went to the logfile?  In
which case, just don't change it in your child..

-- 
- Gus