Help -- how to fork an Apache process in mod_perl safely? Not Apache2:Subprocess...

[Victor Danilchenko]

Hi all,

	I need to be able to fork an Apache process in daemon form, to do some 
housekeeping which might potentially take a few seconds. However, when I 
do that, I start getting SQL errors (of the "connection lost" type) in 
the browser. I do the fairly standard cleanup to daemonize the child 
process, but of course it needs to retain the SQL socket open. Here is 
my forking code:


sub modperl_kamikaze_fork () {
# You will have to do CORE::exit(0) at the end of the execution.

$SIG{CHLD} = 'IGNORE';
get_m->flush_buffer;
defined (my $kid = fork) or die "Cannot fork: $!\n";
return $kid if $kid;

my $r = get_r;
close STDIN; open STDIN, '/dev/null'
or die "Can't read /dev/null: $!";
close STDOUT; open STDOUT, '>/dev/null'
or die "Can't write to /dev/null: $!";
close STDERR; open STDERR, '>>/tmp/form.log'
or die "Cannot open /tmp/fork.log\n";
setsid
or die "Can't start a new session: $!";

my $oldfh = select STDERR;
local $| = 1;
select $oldfh;
warn "Child (PID $$) spawned.\n";

$r->child_terminate;
}


	The Apache2:Subprocess doesn't help me, because I need not to spawn an 
external process, but to finish processing in mod_perl context -- just 
without bugging the user with it.


	Any ideas on how to either fork better, or how to solve this without 
forking (e.g. is there a way to 'append' a function call to the request 
after the rest of the request is completed)?


Many thanks in advance.

--
Victor Danilchenko
Senior Software Engineer, AskOnline.net
vic...@askonline.net - 617-273-0119

Re: Help -- how to fork an Apache process in mod_perl safely? Not Apache2:Subprocess...

[Perrin Harkins]

On Tue, Aug 25, 2009 at 8:11 AM, Victor Danilchenko wrote:
>        I need to be able to fork an Apache process in daemon form, to do
> some housekeeping which might potentially take a few seconds. However, when
> I do that, I start getting SQL errors (of the "connection lost" type) in the
> browser. I do the fairly standard cleanup to daemonize the child process,
> but of course it needs to retain the SQL socket open.

You can't fork and keep using a database connection.  You have to open
a new connection in the forked process.

>        The Apache2:Subprocess doesn't help me, because I need not to spawn
> an external process, but to finish processing in mod_perl context -- just
> without bugging the user with it.

In that case, just use a cleanup handler instead.

- Perrin

Re: Help -- how to fork an Apache process in mod_perl safely? Not Apache2:Subprocess...

[Igor Chudov]

my solution is here:

sub fork_temporary_child {
  my $result = fork();
  unless( $result ) {
# Do not use SQL in child
dbh->{InactiveDestroy} = 1;
disconnect_dbh;
  }
  return $result;
}



On Tue, Aug 25, 2009 at 7:11 AM, Victor Danilchenko wrote:

>Hi all,
>
>I need to be able to fork an Apache process in daemon form, to do
> some housekeeping which might potentially take a few seconds. However, when
> I do that, I start getting SQL errors (of the "connection lost" type) in the
> browser. I do the fairly standard cleanup to daemonize the child process,
> but of course it needs to retain the SQL socket open. Here is my forking
> code:
>
> sub modperl_kamikaze_fork () {
># You will have to do CORE::exit(0) at the end of the execution.
>
>$SIG{CHLD} = 'IGNORE';
>get_m->flush_buffer;
>defined (my $kid = fork) or die "Cannot fork: $!\n";
>return $kid if $kid;
>
>my $r = get_r;
>close STDIN; open STDIN, '/dev/null'
>or die "Can't read /dev/null: $!";
>close STDOUT; open STDOUT, '>/dev/null'
>or die "Can't write to /dev/null: $!";
>close STDERR; open STDERR, '>>/tmp/form.log'
>or die "Cannot open /tmp/fork.log\n";
>setsid
>or die "Can't start a new session: $!";
>
>my $oldfh = select STDERR;
>local $| = 1;
>select $oldfh;
>warn "Child (PID $$) spawned.\n";
>
>$r->child_terminate;
> }
>
>
>The Apache2:Subprocess doesn't help me, because I need not to spawn
> an external process, but to finish processing in mod_perl context -- just
> without bugging the user with it.
>
>Any ideas on how to either fork better, or how to solve this without
> forking (e.g. is there a way to 'append' a function call to the request
> after the rest of the request is completed)?
>
>Many thanks in advance.
>
> --
>Victor Danilchenko
>Senior Software Engineer, AskOnline.net
>vic...@askonline.net - 617-273-0119
>

Re: Help -- how to fork an Apache process in mod_perl safely? Not Apache2:Subprocess...

[William T]

There are all kinds of problems that you'll encounter and have to solve if
you fork.  I found it's better to call at(1) to start another seperate
process immediatly.  If you need to pass data JSON worked really well for
me.

-wjt

On Aug 25, 2009 5:12 AM, "Victor Danilchenko"  wrote:

   Hi all,

   I need to be able to fork an Apache process in daemon form, to do
some housekeeping which might potentially take a few seconds. However, when
I do that, I start getting SQL errors (of the "connection lost" type) in the
browser. I do the fairly standard cleanup to daemonize the child process,
but of course it needs to retain the SQL socket open. Here is my forking
code:

sub modperl_kamikaze_fork () {
   # You will have to do CORE::exit(0) at the end of the execution.

   $SIG{CHLD} = 'IGNORE';
   get_m->flush_buffer;
   defined (my $kid = fork) or die "Cannot fork: $!\n";
   return $kid if $kid;

   my $r = get_r;
   close STDIN; open STDIN, '/dev/null'
   or die "Can't read /dev/null: $!";
   close STDOUT; open STDOUT, '>/dev/null'
   or die "Can't write to /dev/null: $!";
   close STDERR; open STDERR, '>>/tmp/form.log'
   or die "Cannot open /tmp/fork.log\n";
   setsid
   or die "Can't start a new session: $!";

   my $oldfh = select STDERR;
   local $| = 1;
   select $oldfh;
   warn "Child (PID $$) spawned.\n";

   $r->child_terminate;
}


   The Apache2:Subprocess doesn't help me, because I need not to spawn
an external process, but to finish processing in mod_perl context -- just
without bugging the user with it.

   Any ideas on how to either fork better, or how to solve this without
forking (e.g. is there a way to 'append' a function call to the request
after the rest of the request is completed)?

   Many thanks in advance.

-- 
   Victor Danilchenko
   Senior Software Engineer, AskOnline.net
   vic...@askonline.net - 617-273-0119

Re: Help -- how to fork an Apache process in mod_perl safely? Not Apache2:Subprocess...

[Victor Danilchenko]

William T wrote:
There are all kinds of problems that you'll encounter and have to solve 
if you fork.  I found it's better to call at(1) to start another 
seperate process immediatly.  If you need to pass data JSON worked 
really well for me.


	Thanks, that's what I ended up doing. First I ended up having to move 
the processing into an external script call anyway, and then I tried 
Apache2::SubProcess, and it ended up working, but my script was randomly 
receiving TERM signals... it's handleable of course, but I decided to go 
with the 'at' technique, it's safer that way, I suppose.




On Aug 25, 2009 5:12 AM, "Victor Danilchenko" > wrote:


   Hi all,

   I need to be able to fork an Apache process in daemon form, to 
do some housekeeping which might potentially take a few seconds. 
However, when I do that, I start getting SQL errors (of the 
"connection lost" type) in the browser. I do the fairly standard 
cleanup to daemonize the child process, but of course it needs to 
retain the SQL socket open. Here is my forking code:


sub modperl_kamikaze_fork () {
   # You will have to do CORE::exit(0) at the end of the execution.

   $SIG{CHLD} = 'IGNORE';
   get_m->flush_buffer;
   defined (my $kid = fork) or die "Cannot fork: $!\n";
   return $kid if $kid;

   my $r = get_r;
   close STDIN; open STDIN, '/dev/null'
   or die "Can't read /dev/null: $!";
   close STDOUT; open STDOUT, '>/dev/null'
   or die "Can't write to /dev/null: $!";
   close STDERR; open STDERR, '>>/tmp/form.log'
   or die "Cannot open /tmp/fork.log\n";
   setsid
   or die "Can't start a new session: $!";

   my $oldfh = select STDERR;
   local $| = 1;
   select $oldfh;
   warn "Child (PID $$) spawned.\n";

   $r->child_terminate;
}


   The Apache2:Subprocess doesn't help me, because I need not to 
spawn an external process, but to finish processing in mod_perl 
context -- just without bugging the user with it.


   Any ideas on how to either fork better, or how to solve this 
without forking (e.g. is there a way to 'append' a function call to 
the request after the rest of the request is completed)?


   Many thanks in advance.

--
   Victor Danilchenko
   Senior Software Engineer, AskOnline.net
   vic...@askonline.net  - 617-273-0119





--
Victor Danilchenko
Senior Software Engineer, AskOnline.net
vic...@askonline.net - 617-273-0119