Re: an update to exec_helper.pl script

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Igor Shevchenko wrote:
> Hi all,
> 
> Some time ago we had a thread about starting long-running background processes 
> from mp2. I've found a race condition in our last solution. The helper 
> background script could be killed by apache cleanup handler before it had a 
> chance to fork into background and do "setsid". Here's the script itself:
> 
> ===start===
> #!/usr/bin/perl -w
> use strict;
> use warnings;
> use POSIX ();
> 
> chdir '/';
> 
> POSIX::setsid;

You mean you have moved the setsid call to an earlier phase? so setsid is 
called before spawn_proc_prog() has returned?

> exit if fork() > 0; # fork once again
> 
> close STDIN;
> open STDOUT, '+>>', '/path/to/apache/error_log'; # any way to get path to the 
> current error_log and pass it in from the caller as an argument or as an 
> opened filehandle ?
> open STDERR, '>&STDOUT';
> 
> exec ( @ARGV ) or die "Failed to exec subprocess: $@\n";
> 
> ===end===
> 
> Here's an updated helper subroutine:
> 
> sub safe_exec {
>     my $in = $apr->spawn_proc_prog ( '/path/to/exec_helper.pl', \@_ );
>     
>     # makes us sleep until the helper is forked into background and it's 
> handlers are untied from us
>     eval { read $in, my($buffer), 1024 };
>     if ( $@ ) {
>         print STDERR "exec error=$@\n";
>     }
>     close $in;
> }
> 
> I had to use this form of spawn_proc_prog to get something to wait on.

but in the normal case where you don't need to get anything from the 
sub-process the above is not needed, no?


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