in reply to Re: CGI and Background Processes
in thread CGI and Background Processes

Thanks, it worked
I still have to decide if this is the way to go, but at least I know that there's a solution
UPDATE:
This seems to work. Unfortunately the background process is supposed to print out to a log. Because STDOUT and STDERR are closed, there is no log.
It seems that I need to think of another option.

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Re^3: CGI and Background Processes
by almut (Canon) on May 05, 2008 at 15:04 UTC
    the background process is supposed to print out to a log

    just reopen STDOUT/STDERR to wherever you want to log to (one of them, or both), instead of closing them...

[reply]
[d/l]
      This doesn't seem to be working for me. This is the code I have now: 
      #!/usr/bin/perl 

use strict;
use warnings;

print "Content-type: text/html\n\n";
print <<END_OF_PAGE;
<HTML>
<HEAD>
    <TITLE>Waiting</TITLE>
</HEAD>
<BODY>
    <P> Waiting Some more </P>
</BODY>
</HTML>
END_OF_PAGE

reopen STDOUT;
reopen STDERR;

system "perl sleep.pl > out ";

      [download]
      The sleeping program is (text book style): 
      use strict;
use warnings;
print "going to sleep\n";
my $i = 0;
while ($i<20){
    sleep (1);
    print "zzz\n";
    $i++;
}
print "finished my beauty sleep\n";

      [download]
      I've also tried to close and the reopen the output streams. I still can't seem to get anything to go to the log file.
      I'm not sure how to use fork() for another process but I can look it up. The question is whether it will fix this problem.
      Any ideas?
[reply]
[d/l]
[select]

        You need to reopen them to somewhere, e.g. something like

        ...

sub background_run {
    my @cmd = @_;
    
    if (my $pid = fork) {
        # parent
        # (...)
        
    } elsif (defined $pid) {      
        # child
        
        # This redirects both STDOUT/STDERR to the same logfile.
        # Instead of appending (">>"), you could of course also
        # create the file anew every time (">"), or create two 
        # separate logfiles, or whatever...

        my $logfile = "/tmp/bgrun.log";
        # re-open STDERR/STDOUT (closes first implicitly)
        # (if this fails, the error msg will end up in Apache's error_
+log)
        open STDERR, ">>", $logfile or die "Couldn't open $logfile: $!
+";
        open STDOUT, ">>", $logfile or die "Couldn't open $logfile: $!
+";

        # optional
        # my $app_path = "/path/to/dir/to/run/long-running-cgi/in";
        # chdir $app_path or die "Couldn't chdir() to $app_path: $!";

        exec @cmd;
        die "Couldn't exec '@cmd': $!";
        
    } else {
        die "Couldn't fork: $!";
    }
}

...
# files (perl, sleep.pl) must be found - in case of doubt,
# use absolute paths...
background_run("perl", "./sleep.pl");
...

        [download]
[reply]
[d/l]

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