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PID of Maxima process needs to be global, so timeout handler has it when
killing the process

#!/usr/bin/perl
#
# The LearningOnline Network with CAPA
# Connect to MAXIMA CAS
#
# $Id: lonmaxima,v 1.11 2006/03/04 15:47:26 www Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#

# 
# http://www.lon-capa.org/
#

 
use IPC::Open3;
use IO::Select;
use IO::Socket;
use IO::File;
use Symbol;
use POSIX;
use lib '/home/httpd/lib/perl/';
use LONCAPA::Configuration;
 
use strict;

# global variables
my $PREFORK                = 5;        # number of children to maintain
my $MAX_CLIENTS_PER_CHILD  = 5;        # number of clients each child should process
my %children               = ();       # keys are current child process IDs
my $children               = 0;        # current number of children
my $status;                            # string for current status
my $pidfile;                           # file containg parent process pid
my $port;                              # path to UNIX socket file
my %perlvar;                           # configuration file info
my $lastlog;                           # last string that was logged
my $maximapid;                         # PID of Maxima process
use vars qw($PREFORK $MAX_CLIENTS_PER_CHILD %children $children $status
	    $pidfile $port %perlvar $lastlog $maximapid);
 
sub maximareply {
    my ($cmd) = @_;
    my $reply='';
    my $error='';
    my $exitstatus='';

    unless ($cmd=~/\;\n$/) { $cmd.=";\n"; }

    my ($cmd_in, $cmd_out, $cmd_err);
    $maximapid = open3($cmd_in, $cmd_out, $cmd_err, 'maxima');
    $children{$maximapid} = 1;
    
    print $cmd_in $cmd;
    close($cmd_in);

    &status("Command sent");

    $SIG{ALRM} = sub { kill(9 => $maximapid); }; 
    alarm(5);

    my $selector = IO::Select->new();

    $selector->add($cmd_err, $cmd_out);
    
    while (my @ready = $selector->can_read()) {
	foreach my $fh (@ready) {
	    if (ref($fh) 
		&& ref($cmd_err)
		&& fileno($fh) == fileno($cmd_err)) {
		$error.=<$cmd_err>;
	    } else {
		my $line = scalar(<$cmd_out>);
                if ($line=~/^(\(\%o|\s)/) {
		    $line=~s/^\(.*\)/     /; 
		    $reply.=$line; 
		}
	    }
	    $selector->remove($fh) if eof($fh);
	}
    }
    alarm(0);
    $SIG{ALRM} = 'DEFAULT';
    if (ref($cmd_out)) { close($cmd_out); }
    if (ref($cmd_err)) { close($cmd_err); }

    &status("Command processed");
    return ($reply,$error,$exitstatus);
}
 
# ------------------------------------------------------------ Service routines 
sub REAPER {                        # takes care of dead children 
                                    # and MAXIMA processes
    $SIG{CHLD} = \&REAPER;
    my $pid = wait;
    $children--;
    delete($children{$pid});
}
 
sub HUNTSMAN {                      # signal handler for SIGINT
    local($SIG{CHLD}) = 'IGNORE';   # we're going to kill our children
    kill('INT' => keys(%children));
    unlink($pidfile);
    unlink($port);
    &logthis('---- Shutdown ----');
    exit;                           # clean up with dignity
}


 
# --------------------------------------------------------------------- Logging
 
sub logthis {
    my ($message)=@_;
    my $execdir=$perlvar{'lonDaemons'};
    my $fh=IO::File->new(">>$execdir/logs/lonmaxima.log");
    my $now=time;
    my $local=localtime($now);
    $lastlog=$local.': '.$message;
    print $fh "$local ($$): $message\n";
}
 
# -------------------------------------------------------------- Status setting
 
sub status {
    my ($what)=@_;
    my $now=time;
    my $local=localtime($now);
    $status=$local.': '.$what;
    $0='lonmaxima: '.$what.' '.$local;
}
 
# -------------------------------------------------------- Escape Special Chars
 
sub escape {
    my ($str)=@_;
    $str =~ s/(\W)/"%".unpack('H2',$1)/eg;
    return $str;
}
 
# ----------------------------------------------------- Un-Escape Special Chars
 
sub unescape {
    my ($str)=@_;
    $str =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
    return $str;
}
 
# ------------------------ grabs exception and records it to log before exiting
sub catchexception {
    my ($signal)=@_;
    $SIG{QUIT}='DEFAULT';
    $SIG{__DIE__}='DEFAULT';
    chomp($signal);
    &logthis("<font color=\"red\">CRITICAL: "
	     ."ABNORMAL EXIT. Child $$ died through "
	     ."\"$signal\"</font>");
    die("Signal abend");
}



# ---------------------------------------------------------------- Main program
# -------------------------------- Set signal handlers to record abnormal exits
 
 
$SIG{'QUIT'}=\&catchexception;
$SIG{__DIE__}=\&catchexception;
 
# ---------------------------------- Read loncapa_apache.conf and loncapa.conf
&status("Read loncapa.conf and loncapa_apache.conf");
%perlvar=%{&LONCAPA::Configuration::read_conf('loncapa.conf')};
 
# ----------------------------- Make sure this process is running from user=www
my $wwwid=getpwnam('www');
if ($wwwid!=$<) {
    my $emailto="$perlvar{'lonAdmEMail'},$perlvar{'lonSysEMail'}";
    my $subj="LON: User ID mismatch";
    system("echo 'User ID mismatch.  lonmaxima must be run as user www.' |\
 mailto $emailto -s '$subj' > /dev/null");
    exit 1;
}
 
# --------------------------------------------- Check if other instance running
 
$pidfile="$perlvar{'lonDaemons'}/logs/lonmaxima.pid";
 
if (-e $pidfile) {
    my $lfh=IO::File->new("$pidfile");
    my $pide=<$lfh>;
    chomp($pide);
    if (kill(0 => $pide)) { die "already running"; }
}

# ------------------------------------------------------- Listen to UNIX socket
&status("Opening socket");
 
$port = "$perlvar{'lonSockDir'}/maximasock";
 
unlink($port);
 

my $server = IO::Socket::UNIX->new(Local  => $port,
				   Type   => SOCK_STREAM,
				   Listen => 10 );
if (!$server) {
    my $st=120+int(rand(240));

    &logthis("<font color=blue>WARNING: ".
	     "Can't make server socket ($st secs):  .. exiting</font>");

    sleep($st);
    exit;
}
    
 
# ---------------------------------------------------- Fork once and dissociate
 
my $fpid=fork;
exit if $fpid;
die("Couldn't fork: $!") unless defined($fpid);
 
POSIX::setsid() or die "Can't start new session: $!";
 
# ------------------------------------------------------- Write our PID on disk
 
my $execdir=$perlvar{'lonDaemons'};
open(PIDSAVE,">$execdir/logs/lonmaxima.pid");
print PIDSAVE "$$\n";
close(PIDSAVE);
&logthis("<font color='red'>CRITICAL: ---------- Starting ----------</font>");
&status('Starting');
     

# Install signal handlers.
$SIG{CHLD} = \&REAPER;
$SIG{INT}  = $SIG{TERM} = \&HUNTSMAN;
 
# Fork off our children.
for (1 .. $PREFORK) {
    &make_new_child($server);
}
 
# And maintain the population.
while (1) {
    &status('Parent process, sleeping');
    sleep;                          # wait for a signal (i.e., child's death)
    for (my $i = $children; $i < $PREFORK; $i++) {
        &status('Parent process, starting child');
        &make_new_child($server);           # top up the child pool
    }
}
                                                                                
sub make_new_child {
    my ($server) = @_;

    # block signal for fork
    my $sigset = POSIX::SigSet->new(SIGINT);
    sigprocmask(SIG_BLOCK, $sigset)
        or die("Can't block SIGINT for fork: $!\n");
     
    die("fork: $!") unless defined(my $pid = fork);
     
    if ($pid) {
        # Parent records the child's birth and returns.
        sigprocmask(SIG_UNBLOCK, $sigset)
            or die("Can't unblock SIGINT for fork: $!\n");
        $children{$pid} = 1;
        $children++;
        return;
    } else {
        # Child can *not* return from this subroutine.
        $SIG{INT} = 'DEFAULT';      # make SIGINT kill us as it did before
     
        # unblock signals
        sigprocmask(SIG_UNBLOCK, $sigset)
            or die("Can't unblock SIGINT for fork: $!\n");

	&process_requests($server);

        # tidy up gracefully and finish

        # this exit is VERY important, otherwise the child will become
        # a producer of more and more children, forking yourself into
        # process death.
        exit;
    }
}

sub process_requests {
    my ($server) = @_;
    # handle connections until we've reached $MAX_CLIENTS_PER_CHILD
    for (my $i=0; $i < $MAX_CLIENTS_PER_CHILD; $i++) {
	&status('Accepting connections');     
	my $client = $server->accept()     or last;
	while (my $cmd=<$client>) {
	    &status('Processing command');
	    print $client &escape((&maximareply(&unescape($cmd)))[0])."\n";
	}
    }    
}