mod_perl, pipes, and "No child processes"

[Tom Servo <to...@cnw.com>]

Hello all.   I'm writing an app that opens a pipe to sendmail, which if
memory serves, forks off a child process of apache to do the pipe, then
exits as soon as it's finished.

I was doing this with MIME::Lite, and it's been working absolutely
splendidly on Linux and on Solaris 7.   However, on Solaris 8 (and I don't
know if this is related to the OS or not) it gives me all sorts of
problems.   Namely, this started after checking the return code on a
MIME::Lite object called $msg after calling the send method.   It usually
returns a 1 on success, but on the new box it was returning 0, despite the
fact that the e-mails were actually going out.

I ended up writing a test on that just opens a filehandle to |
/usr/lib/sendmail -t -ei -eom, then printing to the filehandle, and
closing the filehandle.   If memory serves, it's almost impossible to get
something accurate out of this statement in mod_perl:

open(SENDMAIL, "| /usr/lib/sendmail -t -ei -eom") or do_something();
As that just reports on whether or not an apache child process was able to
spawn, not whether it was actually able to open the pipe to sendmail.

So, that runs fine, then the print works as I actually get the e-mails
it's trying to send, but this bit of code:

close(SENDMAIL) or print STDERR "Filehandle close failed: $!";

spits out: "Filehandle close failed: No child processes"

Any ideas what is causing this?   Like I said, the mail goes out fine, but
it makes it pretty difficult to check the return code since it's always
coming back false.

In a related note, if anyone is feeling generous, do you know if
$SIG{'CHLD'} gets called only when a child process exits on an error, or
does it get called no matter how a child exits, even if it's gracefully
like it's supposed to?

------------
Brian Nilsen
tomservo@cnw.com

[OT] Re: mod_perl, pipes, and "No child processes"

[Jie Gao <J....@isu.usyd.edu.au>]

On Tue, 6 Nov 2001, Tom Servo wrote:

> On Tue, 6 Nov 2001, Luciano Miguel Ferreira Rocha wrote:
>
> > >
> > > I was under the assumption that doing something similar to:
> > >
> > > my $returnval = $msg->send();
> > >
> > > Would give a similar answer.
> > >
> > > I'll give the $? a shot though.   I've noticed that from the shell, it
> > > always has a 0, and that would show up as false under perl...
> >
> > Well, on the shell and every other program, an exit status of 0 means
> > success, and a higher one means an error of some kind.
> >
> > Btw: /bin/false ; echo $? ==> 1
> >      /bin/true  ; echo $? ==> 0
> >
> > Also, the SIGCHLD is sent when a child exits, no matter if in error.
> > You should then check the $? for the reason of the exit and for the
> > return code, if exited normally.
> >
> > Regards,
> >   Luciano Rocha
> >
>
> I've done this now and am getting back a -1 in $?, despite the mail itself
> succeeding.   How can I check the reason for an error code on $? ?

Check the Camel book p134 "Global Special Variables" (2nd ed).

Regards,



Jie

Re: mod_perl, pipes, and "No child processes"

[Tom Servo <to...@cnw.com>]

On Tue, 6 Nov 2001, Luciano Miguel Ferreira Rocha wrote:

> > 
> > I was under the assumption that doing something similar to:
> > 
> > my $returnval = $msg->send();
> > 
> > Would give a similar answer.
> > 
> > I'll give the $? a shot though.   I've noticed that from the shell, it
> > always has a 0, and that would show up as false under perl...
> 
> Well, on the shell and every other program, an exit status of 0 means
> success, and a higher one means an error of some kind.
> 
> Btw: /bin/false ; echo $? ==> 1
>      /bin/true  ; echo $? ==> 0
> 
> Also, the SIGCHLD is sent when a child exits, no matter if in error.
> You should then check the $? for the reason of the exit and for the
> return code, if exited normally.
> 
> Regards,
>   Luciano Rocha
> 

I've done this now and am getting back a -1 in $?, despite the mail itself
succeeding.   How can I check the reason for an error code on $? ?

Re: mod_perl, pipes, and "No child processes"

[Luciano Miguel Ferreira Rocha <st...@nsk.yi.org>]

> 
> I was under the assumption that doing something similar to:
> 
> my $returnval = $msg->send();
> 
> Would give a similar answer.
> 
> I'll give the $? a shot though.   I've noticed that from the shell, it
> always has a 0, and that would show up as false under perl...

Well, on the shell and every other program, an exit status of 0 means
success, and a higher one means an error of some kind.

Btw: /bin/false ; echo $? ==> 1
     /bin/true  ; echo $? ==> 0

Also, the SIGCHLD is sent when a child exits, no matter if in error.
You should then check the $? for the reason of the exit and for the
return code, if exited normally.

Regards,
  Luciano Rocha

-- 
Luciano Rocha, strange@nsk.yi.org

The trouble with computers is that they do what you tell them, not what
you want.
                -- D. Cohen

Re: mod_perl, pipes, and "No child processes"

[Tom Servo <to...@cnw.com>]

> > > Any ideas what is causing this?  Like I said, the mail goes out
> fine, but > it makes it pretty difficult to check the return code since
> it's always > coming back false. 
> 
> Shouldn't you check $? instead?
> 

I was under the assumption that doing something similar to:

my $returnval = $msg->send();

Would give a similar answer.

I'll give the $? a shot though.   I've noticed that from the shell, it
always has a 0, and that would show up as false under perl...

Re: mod_perl, pipes, and "No child processes"

[Jie Gao <J....@isu.usyd.edu.au>]

On Tue, 6 Nov 2001, Tom Servo wrote:

> Hello all.   I'm writing an app that opens a pipe to sendmail, which if
> memory serves, forks off a child process of apache to do the pipe, then
> exits as soon as it's finished.
>
> I was doing this with MIME::Lite, and it's been working absolutely
> splendidly on Linux and on Solaris 7.   However, on Solaris 8 (and I don't
> know if this is related to the OS or not) it gives me all sorts of
> problems.   Namely, this started after checking the return code on a
> MIME::Lite object called $msg after calling the send method.   It usually
> returns a 1 on success, but on the new box it was returning 0, despite the
> fact that the e-mails were actually going out.
>
> I ended up writing a test on that just opens a filehandle to |
> /usr/lib/sendmail -t -ei -eom, then printing to the filehandle, and
> closing the filehandle.   If memory serves, it's almost impossible to get
> something accurate out of this statement in mod_perl:
>
> open(SENDMAIL, "| /usr/lib/sendmail -t -ei -eom") or do_something();
> As that just reports on whether or not an apache child process was able to
> spawn, not whether it was actually able to open the pipe to sendmail.
>
> So, that runs fine, then the print works as I actually get the e-mails
> it's trying to send, but this bit of code:
>
> close(SENDMAIL) or print STDERR "Filehandle close failed: $!";
>
> spits out: "Filehandle close failed: No child processes"
>
> Any ideas what is causing this?   Like I said, the mail goes out fine, but
> it makes it pretty difficult to check the return code since it's always
> coming back false.

Shouldn't you check $? instead?



Jie