File:  [LON-CAPA] / loncom / loncnew
Revision 1.72: download - view: text, annotated - select for diffs
Mon Aug 29 18:22:48 2005 UTC (17 years, 1 month ago) by albertel
Branches: MAIN
CVS tags: version_2_1_1, version_2_1_0, version_2_0_X, version_2_0_99_1, version_2_0_2, version_2_0_1, HEAD
- upping the default number of connection attempts made

# The LearningOnline Network with CAPA
# lonc maintains the connections to remote computers
# $Id: loncnew,v 1.72 2005/08/29 18:22:48 albertel 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
# 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
# new lonc handles n request out bver m connections to londs.
# This module is based on the Event class.
#   Development iterations:
#    - Setup basic event loop.   (done)
#    - Add timer dispatch.       (done)
#    - Add ability to accept lonc UNIX domain sockets.  (done)
#    - Add ability to create/negotiate lond connections (done).
#    - Add general logic for dispatching requests and timeouts. (done).
#    - Add support for the lonc/lond requests.          (done).
#    - Add logging/status monitoring.                    (done)
#    - Add Signal handling - HUP restarts. USR1 status report. (done)
#    - Add Configuration file I/O                       (done).
#    - Add management/status request interface.         (done)
#    - Add deferred request capability.                  (done)
#    - Detect transmission timeouts.                     (done)

use strict;
use lib "/home/httpd/lib/perl/";
use Event qw(:DEFAULT );
use POSIX qw(:signal_h);
use POSIX;
use IO::Socket;
use IO::Socket::INET;
use IO::Socket::UNIX;
use IO::File;
use IO::Handle;
use Socket;
use Crypt::IDEA;
use LONCAPA::Queue;
use LONCAPA::Stack;
use LONCAPA::LondConnection;
use LONCAPA::LondTransaction;
use LONCAPA::Configuration;
use LONCAPA::HashIterator;
use Fcntl qw(:flock);

# Read the httpd configuration file to get perl variables
# normally set in apache modules:

my $perlvarref = LONCAPA::Configuration::read_conf('loncapa.conf');
my %perlvar    = %{$perlvarref};

#  parent and shared variables.

my %ChildHash;			# by pid -> host.
my %HostToPid;			# By host -> pid.
my %HostHash;			# by loncapaname -> IP.
my %listening_to;		# Socket->host table for who the parent
                                # is listening to.
my %parent_dispatchers;         # host-> listener watcher events. 

my %parent_handlers;		# Parent signal handlers...

my $MaxConnectionCount = 10;	# Will get from config later.
my $ClientConnection = 0;	# Uniquifier for client events.

my $DebugLevel = 0;
my $NextDebugLevel= 2;		# So Sigint can toggle this.
my $IdleTimeout= 600;		# Wait 10 minutes before pruning connections.

my $LogTransactions = 0;	# When True, all transactions/replies get logged.
my $executable      = $0;	# Get the full path to me.

#  The variables below are only used by the child processes.
my $RemoteHost;			# Name of host child is talking to.
my $UnixSocketDir= $perlvar{'lonSockDir'};
my $IdleConnections = Stack->new(); # Set of idle connections
my %ActiveConnections;		# Connections to the remote lond.
my %ActiveTransactions;		# LondTransactions in flight.
my %ActiveClients;		# Serial numbers of active clients by socket.
my $WorkQueue       = Queue->new(); # Queue of pending transactions.
my $ConnectionCount = 0;
my $IdleSeconds     = 0;	# Number of seconds idle.
my $Status          = "";	# Current status string.
my $RecentLogEntry  = "";
my $ConnectionRetries=5;	# Number of connection retries allowed.
my $ConnectionRetriesLeft=5;	# Number of connection retries remaining.
my $LondVersion     = "unknown"; # Version of lond we talk with.
my $KeyMode         = "";       # e.g. ssl, local, insecure from last connect.
my $LondConnecting  = 0;       # True when a connection is being built.

my $DieWhenIdle     = 1;	# When true children die when trimmed -> 0.
my $I_am_child      = 0;	# True if this is the child process.

#   The hash below gives the HTML format for log messages
#   given a severity.
my %LogFormats;

$LogFormats{"CRITICAL"} = "<font color='red'>CRITICAL: %s</font>";
$LogFormats{"SUCCESS"}  = "<font color='green'>SUCCESS: %s</font>";
$LogFormats{"INFO"}     = "<font color='yellow'>INFO: %s</font>";
$LogFormats{"WARNING"}  = "<font color='blue'>WARNING: %s</font>";
$LogFormats{"DEFAULT"}  = " %s ";

#  UpdateStatus;
#    Update the idle status display to show how many connections
#    are left, retries and other stuff.
sub UpdateStatus {
    if ($ConnectionRetriesLeft > 0) {
	ShowStatus(GetServerHost()." Connection count: ".$ConnectionCount
		   ." Retries remaining: ".$ConnectionRetriesLeft
		   ." ($KeyMode)");
    } else {
	ShowStatus(GetServerHost()." >> DEAD <<");


=head2 LogPerm

Makes an entry into the permanent log file.


sub LogPerm {
    my $message=shift;
    my $execdir=$perlvar{'lonDaemons'};
    my $now=time;
    my $local=localtime($now);
    my $fh=IO::File->new(">>$execdir/logs/lonnet.perm.log");
    print $fh "$now:$message:$local\n";


=head2 Log

Logs a message to the log file.

=item severity

One of CRITICAL, WARNING, INFO, SUCCESS used to select the
format string used to format the message.  if the severity is
not a defined severity the Default format string is used.

=item message

The base message.  In addtion to the format string, the message
will be appended to a string containing the name of our remote
host and the time will be formatted into the message.


sub Log {

    my ($severity, $message) = @_;

    if(!$LogFormats{$severity}) {
	$severity = "DEFAULT";

    my $format = $LogFormats{$severity};
    #  Put the window dressing in in front of the message format:

    my $now   = time;
    my $local = localtime($now);
    my $finalformat = "$local ($$) [$RemoteHost] [$Status] ";
    my $finalformat = $finalformat.$format."\n";

    # open the file and put the result.

    my $execdir = $perlvar{'lonDaemons'};
    my $fh      = IO::File->new(">>$execdir/logs/lonc.log");
    my $msg = sprintf($finalformat, $message);
    $RecentLogEntry = $msg;
    print $fh $msg;


=head2 GetPeerName

Returns the name of the host that a socket object is connected to.


sub GetPeername {

    my ($connection, $AdrFamily) = @_;

    my $peer       = $connection->peername();
    my $peerport;
    my $peerip;
    if($AdrFamily == AF_INET) {
	($peerport, $peerip) = sockaddr_in($peer);
	my $peername    = gethostbyaddr($peerip, $AdrFamily);
	return $peername;
    } elsif ($AdrFamily == AF_UNIX) {
	my $peerfile;
	($peerfile) = sockaddr_un($peer);
	return $peerfile;

=head2 Debug

Invoked to issue a debug message.


sub Debug {

    my ($level, $message) = @_;

    if ($level <= $DebugLevel) {
	Log("INFO", "-Debug- $message host = $RemoteHost");

sub SocketDump {

    my ($level, $socket) = @_;

    if($level <= $DebugLevel) {
	$socket->Dump(-1);	# Ensure it will get dumped.


=head2 ShowStatus

 Place some text as our pid status.
 and as what we return in a SIGUSR1


sub ShowStatus {
    my $state = shift;
    my $now = time;
    my $local = localtime($now);
    $Status   = $local.": ".$state;
    $0='lonc: '.$state.' '.$local;


=head2 SocketTimeout

    Called when an action on the socket times out.  The socket is 
   destroyed and any active transaction is failed.


sub SocketTimeout {
    my $Socket = shift;
    Log("WARNING", "A socket timeout was detected");
    Debug(5, " SocketTimeout called: ");
    if(exists($ActiveTransactions{$Socket})) {
    KillSocket($Socket);	# A transaction timeout also counts as
                                # a connection failure:
    if($ConnectionRetriesLeft <= 0) {
	Log("CRITICAL", "Host marked DEAD: ".GetServerHost());
	$LondConnecting = 0;

#   This function should be called by the child in all cases where it must
#   exit.  If the child process is running with the DieWhenIdle turned on
#   it must create a lock file for the AF_UNIX socket in order to prevent
#   connection requests from lonnet in the time between process exit
#   and the parent picking up the listen again.
# Parameters:
#     exit_code           - Exit status value, however see the next parameter.
#     message             - If this optional parameter is supplied, the exit
#                           is via a die with this message.
sub child_exit {
    my ($exit_code, $message) = @_;

    # Regardless of how we exit, we may need to do the lock thing:

    if($DieWhenIdle) {
	#  Create a lock file since there will be a time window
	#  between our exit and the parent's picking up the listen
	#  during which no listens will be done on the
	#  lonnet client socket.
	my $lock_file = GetLoncSocketPath().".lock";
	print LOCK "Contents not important";
    #  Now figure out how we exit:

    if($message) {
	die $message;
    } else {
#----------------------------- Timer management ------------------------


=head2 Tick

Invoked  each timer tick.


sub Tick {
    my ($Event)       = @_;
    my $clock_watcher = $Event->w;

    my $client;

    # Is it time to prune connection count:

    if($IdleConnections->Count()  && 
       ($WorkQueue->Count() == 0)) { # Idle connections and nothing to do?
	if($IdleSeconds > $IdleTimeout) { # Prune a connection...
	    my $Socket = $IdleConnections->pop();
	    $IdleSeconds = 0;	# Otherwise all connections get trimmed to fast.
	    if(($ConnectionCount == 0) && $DieWhenIdle) {

    } else {
	$IdleSeconds = 0;	# Reset idle count if not idle.
    #  For each inflight transaction, tick down its timeout counter.

    foreach my $item (keys %ActiveConnections) {
	my $State = $ActiveConnections{$item}->data->GetState();
	if ($State ne 'Idle') {
	    Debug(5,"Ticking Socket $State $item");
    # Do we have work in the queue, but no connections to service them?
    # If so, try to make some new connections to get things going again.
    #   Note this code is dead now...
    my $Requests = $WorkQueue->Count();
    if (($ConnectionCount == 0)  && ($Requests > 0) && (!$LondConnecting)) { 
	if ($ConnectionRetriesLeft > 0) {
	    Debug(5,"Work but no connections, Make a new one");
	    my $success;
	    $success    = &MakeLondConnection;
	    if($success == 0) { # All connections failed:
		Debug(5,"Work in queue failed to make any connectiouns\n");
		EmptyQueue();	# Fail pending transactions with con_lost.
		CloseAllLondConnections(); # Should all be closed but....
	} else {
	    $LondConnecting = 0;
	    ShowStatus(GetServerHost()." >>> DEAD!!! <<<");
	    Debug(5,"Work in queue, but gave up on connections..flushing\n");
	    EmptyQueue();	# Connections can't be established.
	    CloseAllLondConnections(); # Should all already be closed but...
    if ($ConnectionCount == 0) {
	$KeyMode = ""; 


=head2 SetupTimer

Sets up a 1 per sec recurring timer event.  The event handler is used to:


Trigger timeouts on communications along active sockets.


Trigger disconnections of idle sockets.


sub SetupTimer {
    Debug(6, "SetupTimer");
    Event->timer(interval => 1, cb => \&Tick );


=head2 ServerToIdle

This function is called when a connection to the server is
ready for more work.

If there is work in the Work queue the top element is dequeued
and the connection will start to work on it.  If the work queue is
empty, the connection is pushed on the idle connection stack where
it will either get another work unit, or alternatively, if it sits there
long enough, it will be shut down and released.


sub ServerToIdle {
    my $Socket   = shift;	# Get the socket.
    $KeyMode = $Socket->{AuthenticationMode};
    delete($ActiveTransactions{$Socket}); # Server has no transaction

    &Debug(5, "Server to idle");

    #  If there's work to do, start the transaction:

    my $reqdata = $WorkQueue->dequeue(); # This is a LondTransaction
    if ($reqdata ne undef)  {
	Debug(5, "Queue gave request data: ".$reqdata->getRequest());
	&StartRequest($Socket,  $reqdata);

    } else {
    #  There's no work waiting, so push the server to idle list.
	&Debug(5, "No new work requests, server connection going idle");


=head2 ClientWritable

Event callback for when a client socket is writable.

This callback is established when a transaction reponse is
avaiable from lond.  The response is forwarded to the unix socket
as it becomes writable in this sub.


=item Event

The event that has been triggered. Event->w->data is
the data and Event->w->fd is the socket to write.


sub ClientWritable {
    my $Event    = shift;
    my $Watcher  = $Event->w;
    my $Data     = $Watcher->data;
    my $Socket   = $Watcher->fd;

    # Try to send the data:

    &Debug(6, "ClientWritable writing".$Data);
    &Debug(9, "Socket is: ".$Socket);

    if($Socket->connected) {
	my $result = $Socket->send($Data, 0);
	# $result undefined: the write failed.
	# otherwise $result is the number of bytes written.
	# Remove that preceding string from the data.
	# If the resulting data is empty, destroy the watcher
	# and set up a read event handler to accept the next
	# request.
	&Debug(9,"Send result is ".$result." Defined: ".defined($result));
	if($result ne undef) {
	    &Debug(9, "send result was defined");
	    if($result == length($Data)) { # Entire string sent.
		&Debug(9, "ClientWritable data all written");
		#  Set up to read next request from socket:
		my $descr     = sprintf("Connection to lonc client %d",
		Event->io(cb    => \&ClientRequest,
			  poll  => 'r',
			  desc  => $descr,
			  data  => "",
			  fd    => $Socket);
	    } else {		# Partial string sent.
		$Watcher->data(substr($Data, $result));
		if($result == 0) {    # client hung up on us!!
		    # Log("INFO", "lonc pipe client hung up on us!");
	} else {			# Error of some sort...
	    # Some errnos are possible:
	    my $errno = $!;
	    if($errno == POSIX::EWOULDBLOCK   ||
	       $errno == POSIX::EAGAIN        ||
	       $errno == POSIX::EINTR) {
		# No action taken?
	    } else {		# Unanticipated errno.
		&Debug(5,"ClientWritable error or peer shutdown".$RemoteHost);
		$Watcher->cancel;	# Stop the watcher.
		$Socket->shutdown(2); # Kill connection
		$Socket->close();	# Close the socket.
    } else {
	$Watcher->cancel();	# A delayed request...just cancel.


=head2 CompleteTransaction

Called when the reply data has been received for a lond 
transaction.   The reply data must now be sent to the
ultimate client on the other end of the Unix socket.  This is
done by setting up a writable event for the socket with the
data the reply data.


=item Socket

Socket on which the lond transaction occured.  This is a
LondConnection. The data received is in the TransactionReply member.

=item Transaction

The transaction that is being completed.


sub CompleteTransaction {
    &Debug(5,"Complete transaction");

    my ($Socket, $Transaction) = @_;

    if (!$Transaction->isDeferred()) { # Normal transaction
	my $data   = $Socket->GetReply(); # Data to send.
	if($LogTransactions) {
	    Log("SUCCESS", "Reply from lond: '$data'");
	StartClientReply($Transaction, $data);
    } else {			# Delete deferred transaction file.
	Log("SUCCESS", "A delayed transaction was completed");
	LogPerm("S:$Transaction->getClient() :".$Transaction->getRequest());
	unlink $Transaction->getFile();


=head1 StartClientReply

   Initiates a reply to a client where the reply data is a parameter.

=head2  parameters:

=item Transaction

    The transaction for which we are responding to the client.

=item data

    The data to send to apached client.


sub StartClientReply {

    my ($Transaction, $data) = @_;

    my $Client   = $Transaction->getClient();

    &Debug(8," Reply was: ".$data);
    my $Serial         = $ActiveClients{$Client};
    my $desc           = sprintf("Connection to lonc client %d",
    Event->io(fd       => $Client,
	      poll     => "w",
	      desc     => $desc,
	      cb       => \&ClientWritable,
	      data     => $data);


=head2 FailTransaction

  Finishes a transaction with failure because the associated lond socket
  disconnected.  There are two possibilities:
  - The transaction is deferred: in which case we just quietly
    delete the transaction since there is no client connection.
  - The transaction is 'live' in which case we initiate the sending
    of "con_lost" to the client.

Deleting the transaction means killing it from the %ActiveTransactions hash.


=item client  
   The LondTransaction we are failing.


sub FailTransaction {
    my $transaction = shift;
    #  If the socket is dead, that's already logged.

    if ($ConnectionRetriesLeft > 0) {
	Log("WARNING", "Failing transaction "
    Debug(1, "Failing transaction: ".$transaction->getLoggableRequest());
    if (!$transaction->isDeferred()) { # If the transaction is deferred we'll get to it.
	my $client  = $transaction->getClient();
	Debug(1," Replying con_lost to ".$transaction->getRequest());
	StartClientReply($transaction, "con_lost\n");



=head1  EmptyQueue

  Fails all items in the work queue with con_lost.
  Note that each item in the work queue is a transaction.


sub EmptyQueue {
    $ConnectionRetriesLeft--;	# Counts as connection failure too.
    while($WorkQueue->Count()) {
	my $request = $WorkQueue->dequeue(); # This is a transaction


=head2 CloseAllLondConnections

Close all connections open on lond prior to exit e.g.


sub CloseAllLondConnections {
    foreach my $Socket (keys %ActiveConnections) {
      if(exists($ActiveTransactions{$Socket})) {


=head2 KillSocket
Destroys a socket.  This function can be called either when a socket
has died of 'natural' causes or because a socket needs to be pruned due to
idleness.  If the socket has died naturally, if there are no longer any 
live connections a new connection is created (in case there are transactions
in the queue).  If the socket has been pruned, it is never re-created.


=item Socket
  The socket to kill off.

=item Restart

nonzero if we are allowed to create a new connection.


sub KillSocket {
    my $Socket = shift;

    Log("WARNING", "Shutting down a socket");

    #  If the socket came from the active connection set,
    #  delete its transaction... note that FailTransaction should
    #  already have been called!!!
    #  otherwise it came from the idle set.
    if(exists($ActiveTransactions{$Socket})) {
	delete ($ActiveTransactions{$Socket});
    if(exists($ActiveConnections{$Socket})) {
	if ($ConnectionCount < 0) { $ConnectionCount = 0; }
    #  If the connection count has gone to zero and there is work in the
    #  work queue, the work all gets failed with con_lost.
    if($ConnectionCount == 0) {
	CloseAllLondConnections; # Should all already be closed but...


=head2 LondReadable

This function is called whenever a lond connection
is readable.  The action is state dependent:

=head3 State=Initialized

We''re waiting for the challenge, this is a no-op until the
state changes.

=head3 State=Challenged 

The challenge has arrived we need to transition to Writable.
The connection must echo the challenge back.

=head3 State=ChallengeReplied

The challenge has been replied to.  The we are receiveing the 
'ok' from the partner.

=head3  State=ReadingVersionString

We have requested the lond version and are reading the
version back.  Upon completion, we'll store the version away
for future use(?).

=head3 State=HostSet

We have selected the domain name of our peer (multhomed hosts)
and are getting the reply (presumably ok) back.

=head3 State=RequestingKey

The ok has been received and we need to send the request for
an encryption key.  Transition to writable for that.

=head3 State=ReceivingKey

The the key has been requested, now we are reading the new key.

=head3 State=Idle 

The encryption key has been negotiated or we have finished 
reading data from the a transaction.   If the callback data has
a client as well as the socket iformation, then we are 
doing a transaction and the data received is relayed to the client
before the socket is put on the idle list.

=head3 State=SendingRequest

I do not think this state can be received here, but if it is,
the appropriate thing to do is to transition to writable, and send
the request.

=head3 State=ReceivingReply

We finished sending the request to the server and now transition
to readable to receive the reply. 

The parameter to this function are:

The event. Implicit in this is the watcher and its data.  The data 
contains at least the lond connection object and, if a 
transaction is in progress, the socket attached to the local client.


sub LondReadable {

    my $Event      = shift;
    my $Watcher    = $Event->w;
    my $Socket     = $Watcher->data;
    my $client     = undef;

    &Debug(6,"LondReadable called state = ".$Socket->GetState());

    my $State = $Socket->GetState(); # All action depends on the state.

    SocketDump(6, $Socket);
    my $status = $Socket->Readable();

    &Debug(2, "Socket->Readable returned: $status");

    if($status != 0) {
	# bad return from socket read. Currently this means that
	# The socket has become disconnected. We fail the transaction.

	    "Lond connection lost.");
	if(exists($ActiveTransactions{$Socket})) {
	} else {
	    #  Socket is connecting and failed... need to mark
	    #  no longer connecting.
	    $LondConnecting = 0;
	$ConnectionRetriesLeft--;       # Counts as connection failure

    $State = $Socket->GetState(); # Update in case of transition.
    &Debug(6, "After read, state is ".$State);

    if($State eq "Initialized") {

    } elsif ($State eq "ChallengeReceived") {
	#  The challenge must be echoed back;  The state machine
	# in the connection takes care of setting that up.  Just
	# need to transition to writable:

    } elsif ($State eq "ChallengeReplied") {

    } elsif ($State eq "RequestingVersion") {
	# Need to ask for the version... that is writiability:


    } elsif ($State eq "ReadingVersionString") {
	# Read the rest of the version string... 
    } elsif ($State eq "SetHost") {
	# Need to request the actual domain get set...

    } elsif ($State eq "HostSet") {
	# Reading the 'ok' from the peer.

    } elsif ($State eq "RequestingKey") {
	#  The ok was received.  Now we need to request the key
	#  That requires us to be writable:


    } elsif ($State eq "ReceivingKey") {

    } elsif ($State eq "Idle") {
	# This is as good a spot as any to get the peer version
	# string:
	if($LondVersion eq "unknown") {
	    $LondVersion = $Socket->PeerVersion();
	    Log("INFO", "Connected to lond version: $LondVersion");
	# If necessary, complete a transaction and then go into the
	# idle queue.
	#  Note that a trasition to idle indicates a live lond
	# on the other end so reset the connection retries.
	$ConnectionRetriesLeft = $ConnectionRetries; # success resets the count
	if(exists($ActiveTransactions{$Socket})) {
	    Debug(5,"Completing transaction!!");
	} else {
	    Log("SUCCESS", "Connection ".$ConnectionCount." to "
		.$RemoteHost." now ready for action");
	ServerToIdle($Socket);	# Next work unit or idle.

	$LondConnecting = 0;	# Best spot I can think of for this.
    } elsif ($State eq "SendingRequest") {
	#  We need to be writable for this and probably don't belong
	#  here inthe first place.

	Deubg(6, "SendingRequest state encountered in readable");

    } elsif ($State eq "ReceivingReply") {

    } else {
	# Invalid state.
	Debug(4, "Invalid state in LondReadable");


=head2 LondWritable

This function is called whenever a lond connection
becomes writable while there is a writeable monitoring
event.  The action taken is very state dependent:

=head3 State = Connected 

The connection is in the process of sending the 'init' hailing to the
lond on the remote end.  The connection object''s Writable member is
called.  On error, ConnectionError is called to destroy the connection
and remove it from the ActiveConnections hash

=head3 Initialized

'init' has been sent, writability monitoring is removed and
readability monitoring is started with LondReadable as the callback.

=head3 ChallengeReceived

The connection has received the who are you challenge from the remote
system, and is in the process of sending the challenge
response. Writable is called.

=head3 ChallengeReplied

The connection has replied to the initial challenge The we switch to
monitoring readability looking for the server to reply with 'ok'.

=head3 RequestingKey

The connection is in the process of requesting its encryption key.
Writable is called.

=head3 ReceivingKey

The connection has sent the request for a key.  Switch to readability
monitoring to accept the key

=head3 SendingRequest

The connection is in the process of sending a request to the server.
This request is part of a client transaction.  All the states until
now represent the client setup protocol. Writable is called.

=head3 ReceivingReply

The connection has sent a request.  Now it must receive a reply.
Readability monitoring is requested.

This function is an event handler and therefore receives as
a parameter the event that has fired.  The data for the watcher
of this event is a reference to a list of one or two elements,
depending on state. The first (and possibly only) element is the
socket.  The second (present only if a request is in progress)
is the socket on which to return a reply to the caller.


sub LondWritable {
    my $Event   = shift;
    my $Watcher = $Event->w;
    my $Socket  = $Watcher->data;
    my $State   = $Socket->GetState();

    Debug(6,"LondWritable State = ".$State."\n");

    #  Figure out what to do depending on the state of the socket:


    #  If the socket is writable, we must always write.
    # Only by writing will we undergo state transitions.
    # Old logic wrote in state specific code below, however
    # That forces us at least through another invocation of
    # this function after writability is possible again.
    # This logic also factors out common code for handling
    # write failures... in all cases, write failures 
    # Kill the socket.
    #  This logic makes the branches of the >big< if below
    # so that the writing states are actually NO-OPs.

    if ($Socket->Writable() != 0) {
	#  The write resulted in an error.
	# We'll treat this as if the socket got disconnected:
	Log("WARNING", "Connection to ".$RemoteHost.
	    " has been disconnected");
	if(exists($ActiveTransactions{$Socket})) {
	} else {
	    #  In the process of conneting, so need to turn that off.
	    $LondConnecting = 0;

    if      ($State eq "Connected")         {

	#  "init" is being sent...
    } elsif ($State eq "Initialized")       {

	# Now that init was sent, we switch 
	# to watching for readability:

    } elsif ($State eq "ChallengeReceived") {
	# We received the challenge, now we 
	# are echoing it back. This is a no-op,
	# we're waiting for the state to change
    } elsif ($State eq "ChallengeReplied")  {
	# The echo was sent back, so we switch
	# to watching readability.

    } elsif ($State eq "RequestingVersion") {
	# Sending the peer a version request...

    } elsif ($State eq "ReadingVersionString") {
	# Transition to read since we have sent the
	# version command and now just need to read the
	# version string from the peer:
    } elsif ($State eq "SetHost") {
	#  Setting the remote domain...

    } elsif ($State eq "HostSet") {
	# Back to readable to get the ok.

    } elsif ($State eq "RequestingKey")     {
	# At this time we're requesting the key.
	# again, this is essentially a no-op.

    } elsif ($State eq "ReceivingKey")      {
	# Now we need to wait for the key
	# to come back from the peer:


    } elsif ($State eq "SendingRequest")    {
	# At this time we are sending a request to the
	# peer... write the next chunk:

    } elsif ($State eq "ReceivingReply")    {
	# The send has completed.  Wait for the
	# data to come in for a reply.
	Debug(8,"Writable sent request/receiving reply");

    } else {
	#  Control only passes here on an error: 
	#  the socket state does not match any
	#  of the known states... so an error
	#  must be logged.

	&Debug(4, "Invalid socket state ".$State."\n");

sub QueueDelayed {
    Debug(3,"QueueDelayed called");

    my $path = "$perlvar{'lonSockDir'}/delayed";

    Debug(4, "Delayed path: ".$path);
    opendir(DIRHANDLE, $path);
    my @alldelayed = grep /\.$RemoteHost$/, readdir DIRHANDLE;
    my $dfname;
    my $reqfile;
    foreach $dfname (sort  @alldelayed) {
	$reqfile = "$path/$dfname";
	Debug(4, "queueing ".$reqfile);
	my $Handle = IO::File->new($reqfile);
	my $cmd    = <$Handle>;
	chomp $cmd;		# There may or may not be a newline...
	$cmd = $cmd."\n";	# now for sure there's exactly one newline.
	my $Transaction = LondTransaction->new($cmd);


=head2 MakeLondConnection

Create a new lond connection object, and start it towards its initial
idleness.  Once idle, it becomes elligible to receive transactions
from the work queue.  If the work queue is not empty when the
connection is completed and becomes idle, it will dequeue an entry and
start off on it.


sub MakeLondConnection {     
    Debug(4,"MakeLondConnection to ".GetServerHost()." on port "

    my $Connection = LondConnection->new(&GetServerHost(),

    if($Connection eq undef) {	# Needs to be more robust later.
	Log("CRITICAL","Failed to make a connection with lond.");
	return 0;		# Failure.
    }  else {

	# The connection needs to have writability 
	# monitored in order to send the init sequence
	# that starts the whole authentication/key
	# exchange underway.
	my $Socket = $Connection->GetSocket();
	if($Socket eq undef) {
	    &child_exit(-1, "did not get a socket from the connection");
	} else {
	    &Debug(9,"MakeLondConnection got socket: ".$Socket);

	my $event = Event->io(fd       => $Socket,
			   poll     => 'w',
			   cb       => \&LondWritable,
			   data     => $Connection,
			   desc => 'Connection to lond server');
	$ActiveConnections{$Connection} = $event;
	if ($ConnectionCount == 0) {
	    &SetupTimer;	# Need to handle timeouts with connections...
	Debug(4, "Connection count = ".$ConnectionCount);
	if($ConnectionCount == 1) { # First Connection:
	Log("SUCESS", "Created connection ".$ConnectionCount
	    ." to host ".GetServerHost());
	$LondConnecting = 1;	# Connection in progress.
	return 1;		# Return success.


=head2 StartRequest

Starts a lond request going on a specified lond connection.
parameters are:

=item $Lond

Connection to the lond that will send the transaction and receive the

=item $Client

Connection to the client that is making this request We got the
request from this socket, and when the request has been relayed to
lond and we get a reply back from lond it will get sent to this

=item $Request

The text of the request to send.


sub StartRequest {

    my ($Lond, $Request) = @_;
    Debug(6, "StartRequest: ".$Request->getRequest());

    my $Socket = $Lond->GetSocket();
    $ActiveTransactions{$Lond} = $Request;

    my $event = Event->io(fd      => $Socket,
		       poll    => "w",
		       cb      => \&LondWritable,
		       data    => $Lond,
		       desc    => "lond transaction connection");
    $ActiveConnections{$Lond} = $event;
    Debug(8," Start Request made watcher data with ".$event->data."\n");


=head2 QueueTransaction

If there is an idle lond connection, it is put to work doing this
transaction.  Otherwise, the transaction is placed in the work queue.
If placed in the work queue and the maximum number of connections has
not yet been created, a new connection will be started.  Our goal is
to eventually have a sufficient number of connections that the work
queue will typically be empty.  parameters are:

=item Socket

open on the lonc client.

=item Request

data to send to the lond.


sub QueueTransaction {

    my $requestData   = shift;	# This is a LondTransaction.
    my $cmd           = $requestData->getRequest();

    Debug(6,"QueueTransaction: ".$cmd);

    my $LondSocket    = $IdleConnections->pop();
    if(!defined $LondSocket) {	# Need to queue request.
	Debug(5,"Must queue...");
	Debug(5, "Queue Transaction startnew $ConnectionCount $LondConnecting");
	if(($ConnectionCount < $MaxConnectionCount)   && (! $LondConnecting)) {

	    if($ConnectionRetriesLeft > 0) {
		Debug(5,"Starting additional lond connection");
		if(&MakeLondConnection() == 0) {
		    EmptyQueue();	# Fail transactions, can't make connection.
		    CloseAllLondConnections; # Should all be closed but...
	    } else {
		ShowStatus(GetServerHost()." >>> DEAD !!!! <<<");
		$LondConnecting = 0;
		EmptyQueue();	# It's worse than that ... he's dead Jim.
		CloseAllLondConnections; # Should all be closed but..
    } else {			# Can start the request:
	Debug(8,"Can start...");
	StartRequest($LondSocket,  $requestData);

#-------------------------- Lonc UNIX socket handling ---------------------


=head2 ClientRequest
Callback that is called when data can be read from the UNIX domain
socket connecting us with an apache server process.


sub ClientRequest {
    Debug(6, "ClientRequest");
    my $event   = shift;
    my $watcher = $event->w;
    my $socket  = $watcher->fd;
    my $data    = $watcher->data;
    my $thisread;

    Debug(9, "  Watcher named: ".$watcher->desc);

    my $rv = $socket->recv($thisread, POSIX::BUFSIZ, 0);
    Debug(8, "rcv:  data length = ".length($thisread)
	  ." read =".$thisread);
    unless (defined $rv  && length($thisread)) {
	 # Likely eof on socket.
	Debug(5,"Client Socket closed on lonc for ".$RemoteHost);
    Debug(8,"Data: ".$data." this read: ".$thisread);
    $data = $data.$thisread;	# Append new data.
    if($data =~ /\n$/) {	# Request entirely read.
	if($data eq "close_connection_exit\n") {
		"Request Close Connection ... exiting");
	Debug(8, "Complete transaction received: ".$data);
	if($LogTransactions) {
	    Log("SUCCESS", "Transaction: '$data'"); # Transaction has \n.
	my $Transaction = LondTransaction->new($data);
	$watcher->cancel();	# Done looking for input data.


#     Accept a connection request for a client (lonc child) and
#    start up an event watcher to keep an eye on input from that 
#    Event.  This can be called both from NewClient and from
#    ChildProcess if we are started in DieWhenIdle mode.
# Parameters:
#    $socket       - The listener socket.
# Returns:
#   NONE
# Side Effects:
#    An event is made to watch the accepted connection.
#    Active clients hash is updated to reflect the new connection.
#    The client connection count is incremented.
sub accept_client {
    my ($socket) = @_;

    Debug(8, "Entering accept for lonc UNIX socket\n");
    my $connection = $socket->accept();	# Accept the client connection.
    Debug(8,"Connection request accepted from "
	  .GetPeername($connection, AF_UNIX));

    my $description = sprintf("Connection to lonc client %d",
    Debug(9, "Creating event named: ".$description);
    Event->io(cb      => \&ClientRequest,
	      poll    => 'r',
	      desc    => $description,
	      data    => "",
	      fd      => $connection);
    $ActiveClients{$connection} = $ClientConnection;


=head2  NewClient

Callback that is called when a connection is received on the unix
socket for a new client of lonc.  The callback is parameterized by the
event.. which is a-priori assumed to be an io event, and therefore has
an fd member that is the Listener socket.  We Accept the connection
and register a new event on the readability of that socket:


sub NewClient {
    Debug(6, "NewClient");
    my $event      = shift;		# Get the event parameters.
    my $watcher    = $event->w; 
    my $socket     = $watcher->fd;	# Get the event' socket.



=head2 GetLoncSocketPath

Returns the name of the UNIX socket on which to listen for client

=head2 Parameters:

    host (optional)  - Name of the host socket to return.. defaults to
                       the return from GetServerHost().


sub GetLoncSocketPath {

    my $host = GetServerHost();	# Default host.
    if (@_) {
	($host)  = @_;		# Override if supplied.
    return $UnixSocketDir."/".$host;


=head2 GetServerHost

Returns the host whose lond we talk with.


sub GetServerHost {
    return $RemoteHost;		# Setup by the fork.


=head2 GetServerPort

Returns the lond port number.


sub GetServerPort {
    return $perlvar{londPort};


=head2 SetupLoncListener

Setup a lonc listener event.  The event is called when the socket
becomes readable.. that corresponds to the receipt of a new
connection.  The event handler established will accept the connection
(creating a communcations channel), that int turn will establish
another event handler to subess requests.

=head2  Parameters:

   host (optional)   Name of the host to set up a unix socket to.


sub SetupLoncListener {

    my $host       = GetServerHost(); # Default host.
    if (@_) {
	($host)    = @_		# Override host with parameter.

    my $socket;
    my $SocketName = GetLoncSocketPath($host);
    unless ($socket =IO::Socket::UNIX->new(Local  => $SocketName,
					    Listen => 250, 
					    Type   => SOCK_STREAM)) {
	if($I_am_child) {
	    &child_exit(-1, "Failed to create a lonc listener socket");
	} else {
	    die "Failed to create a lonc listner socket";
    return $socket;

#   Toggle transaction logging.
#  Implicit inputs:  
#     LogTransactions
#  Implicit Outputs:
#     LogTransactions
sub ToggleTransactionLogging {
    print STDERR "Toggle transaction logging...\n";
    if(!$LogTransactions) {
	$LogTransactions = 1;
    } else {
	$LogTransactions = 0;

    Log("SUCCESS", "Toggled transaction logging: $LogTransactions \n");


=head2 ChildStatus
Child USR1 signal handler to report the most recent status
into the status file.

We also use this to reset the retries count in order to allow the
client to retry connections with a previously dead server.


sub ChildStatus {
    my $event = shift;
    my $watcher = $event->w;

    Debug(2, "Reporting child status because : ".$watcher->data);
    my $docdir = $perlvar{'lonDocRoot'};
    print LOG $$."\t".$RemoteHost."\t".$Status."\t".
    #  Write out information about each of the connections:
    if ($DebugLevel > 2) {
	print LOG "Active connection statuses: \n";
	my $i = 1;
	print STDERR  "================================= Socket Status Dump:\n";
	foreach my $item (keys %ActiveConnections) {
	    my $Socket = $ActiveConnections{$item}->data;
	    my $state  = $Socket->GetState();
	    print LOG "Connection $i State: $state\n";
	    print STDERR "---------------------- Connection $i \n";
	    $Socket->Dump(-1);	# Ensure it gets dumped..
    $ConnectionRetriesLeft = $ConnectionRetries;


=head2 SignalledToDeath

Called in response to a signal that causes a chid process to die.


sub SignalledToDeath {
    my $event  = shift;
    my $watcher= $event->w;

    Debug(2,"Signalled to death! via ".$watcher->data);
    my ($signal) = $watcher->data;
    Log("CRITICAL", "Abnormal exit.  Child $$ for $RemoteHost "
	."died through "."\"$signal\"");
    #LogPerm("F:lonc: $$ on $RemoteHost signalled to death: "
#	    ."\"$signal\"");
    exit 0;



=head2 ToggleDebug

This sub toggles trace debugging on and off.


sub ToggleDebug {
    my $Current    = $DebugLevel;
       $DebugLevel = $NextDebugLevel;
       $NextDebugLevel = $Current;

    Log("SUCCESS", "New debugging level for $RemoteHost now $DebugLevel");



=head2 ChildProcess

This sub implements a child process for a single lonc daemon.
Optional parameter:
   $socket  - if provided, this is a socket already open for listen
              on the client socket. Otherwise, a new listen is set up.


sub ChildProcess {
    #  If we are in DieWhenIdle mode, we've inherited all the
    #  events of our parent and those have to be cancelled or else
    #  all holy bloody chaos will result.. trust me, I already made
    #  >that< mistake.

    my $host = GetServerHost();
    foreach my $listener (keys %parent_dispatchers) {
	my $watcher = $parent_dispatchers{$listener};
	my $s       = $watcher->fd;
	if ($listener ne $host) { # Close everyone but me.
	    Debug(5, "Closing listen socket for $listener");
	Debug(5, "Killing watcher for $listener");



    #  kill off the parent's signal handlers too!  

    for my $handler (keys %parent_handlers) {
	my $watcher = $parent_handlers{$handler};

    $I_am_child    = 1;		# Seems like in spite of it all I may still getting
                                # parent event dispatches.. flag I'm a child.

    #  Signals must be handled by the Event framework...

    Event->signal(signal   => "QUIT",
		  cb       => \&SignalledToDeath,
		  data     => "QUIT");
    Event->signal(signal   => "HUP",
		  cb       => \&ChildStatus,
		  data     => "HUP");
    Event->signal(signal   => "USR1",
		  cb       => \&ChildStatus,
		  data     => "USR1");
    Event->signal(signal   => "USR2",
		  cb       => \&ToggleTransactionLogging);
    Event->signal(signal   => "INT",
		  cb       => \&ToggleDebug,
		  data     => "INT");

    #  Figure out if we got passed a socket or need to open one to listen for
    #  client requests.

    my ($socket) = @_;
    if (!$socket) {

	$socket =  SetupLoncListener();
    #  Establish an event to listen for client connection requests.

    Event->io(cb   => \&NewClient,
	      poll => 'r',
	      desc => 'Lonc Listener Unix Socket',
	      fd   => $socket);
    $Event::Debuglevel = $DebugLevel;
    Debug(9, "Making initial lond connection for ".$RemoteHost);

# Setup the initial server connection:
     # &MakeLondConnection(); // let first work request do it.

    #  If We are in diwhenidle, need to accept the connection since the
    #  event may  not fire.

    if ($DieWhenIdle) {

    Debug(9,"Entering event loop");
    my $ret = Event::loop();		#  Start the main event loop.
    &child_exit (-1,"Main event loop exited!!!");

#  Create a new child for host passed in:

sub CreateChild {
    my ($host, $socket) = @_;

    my $sigset = POSIX::SigSet->new(SIGINT);
    sigprocmask(SIG_BLOCK, $sigset);
    $RemoteHost = $host;
    Log("CRITICAL", "Forking server for ".$host);
    my $pid          = fork;
    if($pid) {			# Parent
	$RemoteHost = "Parent";
	$ChildHash{$pid} = $host;
	$HostToPid{$host}= $pid;
	sigprocmask(SIG_UNBLOCK, $sigset);

    } else {			# child.
	ShowStatus("Connected to ".$RemoteHost);
	sigprocmask(SIG_UNBLOCK, $sigset);
	if(defined $socket) {
	} else {
	    ChildProcess;		# Does not return.

# parent_client_connection:
#    Event handler that processes client connections for the parent process.
#    This sub is called when the parent is listening on a socket and
#    a connection request arrives.  We must:
#     Start a child process to accept the connection request.
#     Kill our listen on the socket.
# Parameter:
#    event       - The event object that was created to monitor this socket.
#                  event->w->fd is the socket.
# Returns:
#    NONE
sub parent_client_connection {
    if ($I_am_child) {
	#  Should not get here, but seem to anyway:
	&Debug(5," Child caught parent client connection event!!");
	my ($event) = @_;
	my $watcher = $event->w;
	$watcher->cancel();	# Try to kill it off again!!
    } else {
	&Debug(9, "parent_client_connection");
	my ($event)   = @_;
	my $watcher   = $event->w;
	my $socket    = $watcher->fd;
	# Lookup the host associated with this socket:
	my $host = $listening_to{$socket};
	# Start the child:
	&Debug(9,"Creating child for $host (parent_client_connection)");
	&CreateChild($host, $socket);
	# Clean up the listen since now the child takes over until it exits.
	$watcher->cancel();		# Nolonger listening to this event

# parent_listen:
#    Opens a socket and starts a listen for the parent process on a client UNIX
#    domain socket.
#    This involves:
#       Creating a socket for listen.
#       Removing any socket lock file
#       Adding an event handler for this socket becoming readable
#         To the parent's event dispatcher.
# Parameters:
#    loncapa_host    - LonCAPA cluster name of the host represented by the client
#                      socket.
# Returns:
#    NONE
sub parent_listen {
    my ($loncapa_host) = @_;
    Debug(5, "parent_listen: $loncapa_host");

    my $socket    = &SetupLoncListener($loncapa_host);
    $listening_to{$socket} = $loncapa_host;
    if (!$socket) {
	die "Unable to create a listen socket for $loncapa_host";
    my $lock_file = &GetLoncSocketPath($loncapa_host).".lock";
    unlink($lock_file);		# No problem if it doesn't exist yet [startup e.g.]

    my $watcher = Event->io(cb    => \&parent_client_connection,
	      poll  => 'r',
	      desc  => "Parent listener unix socket ($loncapa_host)",
	      fd    => $socket);
    $parent_dispatchers{$loncapa_host} = $watcher;


# listen_on_all_unix_sockets:
#    This sub initiates a listen on all unix domain lonc client sockets.
#    This will be called in the case where we are trimming idle processes.
#    When idle processes are trimmed, loncnew starts up with no children,
#    and only spawns off children when a connection request occurs on the
#    client unix socket.  The spawned child continues to run until it has
#    been idle a while at which point it eventually exits and once more
#    the parent picks up the listen.
#  Parameters:
#      NONE
#  Implicit Inputs:
#    The configuration file that has been read in by LondConnection.
#  Returns:
#     NONE
sub listen_on_all_unix_sockets {
    Debug(5, "listen_on_all_unix_sockets");
    my $host_iterator      =   &LondConnection::GetHostIterator();
    while (!$host_iterator->end()) {
	my $host_entry_ref =   $host_iterator->get();
	my $host_name      = $host_entry_ref->[0];
	Debug(9, "Listen for $host_name");

#   server_died is called whenever a child process exits.
#   Since this is dispatched via a signal, we must process all
#   dead children until there are no more left.  The action
#   is to:
#      - Remove the child from the bookeeping hashes
#      - Re-establish a listen on the unix domain socket associated
#        with that host.
# Parameters:
#    The event, but we don't actually care about it.
sub server_died {
    &Debug(9, "server_died called...");
    while(1) {			# Loop until waitpid nowait fails.
	my $pid = waitpid(-1, WNOHANG);
	if($pid <= 0) {
	    return;		# Nothing left to wait for.
	# need the host to restart:

	my $host = $ChildHash{$pid};
	if($host) {		# It's for real...
	    &Debug(9, "Caught sigchild for $host");

	} else {
	    &Debug(5, "Caught sigchild for pid not in hosts hash: $pid");


#  Parent process logic pass 1:
#   For each entry in the hosts table, we will
#  fork off an instance of ChildProcess to service the transactions
#  to that host.  Each pid will be entered in a global hash
#  with the value of the key, the host.
#  The parent will then enter a loop to wait for process exits.
#  Each exit gets logged and the child gets restarted.

#   Fork and start in new session so hang-up isn't going to 
#   happen without intent.

ShowStatus("Forming new session");
my $childpid = fork;
if ($childpid != 0) {
    sleep 4;			# Give child a chacne to break to
    exit 0;			# a new sesion.
#   Write my pid into the pid file so I can be located

ShowStatus("Parent writing pid file:");
my $execdir = $perlvar{'lonDaemons'};
open (PIDSAVE, ">$execdir/logs/");
print PIDSAVE "$$\n";

if (POSIX::setsid() < 0) {
    print "Could not create new session\n";
    exit -1;

ShowStatus("Forking node servers");

Log("CRITICAL", "--------------- Starting children ---------------");

LondConnection::ReadConfig;               # Read standard config files.
my $HostIterator = LondConnection::GetHostIterator;

if ($DieWhenIdle) {
    $RemoteHost = "[parent]";
} else {
    while (! $HostIterator->end()) {
	my $hostentryref = $HostIterator->get();
	$HostHash{$hostentryref->[0]} = $hostentryref->[4];

$RemoteHost = "Parent Server";

# Maintain the population:

ShowStatus("Parent keeping the flock");

if ($DieWhenIdle) {
    # We need to setup a SIGChild event to handle the exit (natural or otherwise)
    # of the children.

    Event->signal(cb       => \&server_died,
		   desc     => "Child exit handler",
		   signal   => "CHLD");

    # Set up all the other signals we set up.  We'll vector them off to the
    # same subs as we would for DieWhenIdle false and, if necessary, conditionalize
    # the code there.

    $parent_handlers{INT} = Event->signal(cb       => \&Terminate,
					  desc     => "Parent INT handler",
					  signal   => "INT");
    $parent_handlers{TERM} = Event->signal(cb       => \&Terminate,
					   desc     => "Parent TERM handler",
					   signal   => "TERM");
    $parent_handlers{HUP}  = Event->signal(cb       => \&Restart,
					   desc     => "Parent HUP handler.",
					   signal   => "HUP");
    $parent_handlers{USR1} = Event->signal(cb       => \&CheckKids,
					   desc     => "Parent USR1 handler",
					   signal   => "USR1");
    $parent_handlers{USR2} = Event->signal(cb       => \&UpdateKids,
					   desc     => "Parent USR2 handler.",
					   signal   => "USR2");
    #  Start procdesing events.

    $Event::DebugLevel = $DebugLevel;
    Debug(9, "Parent entering event loop");
    my $ret = Event::loop();
    die "Main Event loop exited: $ret";

} else {
    #   Set up parent signals:
    $SIG{INT}  = \&Terminate;
    $SIG{TERM} = \&Terminate; 
    $SIG{HUP}  = \&Restart;
    $SIG{USR1} = \&CheckKids; 
    $SIG{USR2} = \&UpdateKids;	# LonManage update request.
    while(1) {
	my $deadchild = wait();
	if(exists $ChildHash{$deadchild}) {	# need to restart.
	    my $deadhost = $ChildHash{$deadchild};
	    Log("WARNING","Lost child pid= ".$deadchild.
		"Connected to host ".$deadhost);
	    Log("INFO", "Restarting child procesing ".$deadhost);


=head1 CheckKids

  Since kids do not die as easily in this implementation
as the previous one, there  is no need to restart the
dead ones (all dead kids get restarted when they die!!)
The only thing this function does is to pass USR1 to the
kids so that they report their status.


sub CheckKids {
    Debug(2, "Checking status of children");
    my $docdir = $perlvar{'lonDocRoot'};
    my $fh = IO::File->new(">$docdir/lon-status/loncstatus.txt");
    my $now=time;
    my $local=localtime($now);
    print $fh "LONC status $local - parent $$ \n\n";
    foreach my $host (keys %parent_dispatchers) {
	print $fh "LONC Parent process listening for $host\n";
    foreach my $pid (keys %ChildHash) {
	Debug(2, "Sending USR1 -> $pid");
	kill 'USR1' => $pid;	# Tell Child to report status.



=head1  UpdateKids

parent's SIGUSR2 handler.  This handler:


Rereads the hosts file.

Kills off (via sigint) children for hosts that have disappeared.


QUITs  children for hosts that already exist (this just forces a status display
and resets the connection retry count for that host.


Starts new children for hosts that have been added to the file since
the start of the master program and maintains them.


sub UpdateKids {

    Log("INFO", "Updating connections via SIGUSR2");

    #  I'm not sure what I was thinking in the first implementation.
    # someone will have to work hard to convince me the effect is any
    # different than Restart, especially now that we don't start up 
    # per host servers automatically, may as well just restart.
    # The down side is transactions that are in flight will get timed out
    # (lost unless they are critical).




=head1 Restart

Signal handler for HUP... all children are killed and
we self restart.  This is an el-cheapo way to re read
the config file.


sub Restart {
    &KillThemAll;		# First kill all the children.
    Log("CRITICAL", "Restarting");
    my $execdir = $perlvar{'lonDaemons'};


=head1 KillThemAll

Signal handler that kills all children by sending them a 
SIGHUP.  Responds to sigint and sigterm.


sub KillThemAll {
    Debug(2, "Kill them all!!");
    local($SIG{CHLD}) = 'IGNORE';      # Our children >will< die.
    foreach my $pid (keys %ChildHash) {
	my $serving = $ChildHash{$pid};
	ShowStatus("Nicely Killing lonc for $serving pid = $pid");
	Log("CRITICAL", "Nicely Killing lonc for $serving pid = $pid");
	kill 'QUIT' => $pid;


#  Kill all children via KILL.  Just in case the
#  first shot didn't get them.

sub really_kill_them_all_dammit
    Debug(2, "Kill them all Dammit");
    local($SIG{CHLD} = 'IGNORE'); # In case some purist reenabled them.
    foreach my $pid (keys %ChildHash) {
	my $serving = $ChildHash{$pid};
	&ShowStatus("Nastily killing lonc for $serving pid = $pid");
	Log("CRITICAL", "Nastily killing lonc for $serving pid = $pid");
	kill 'KILL' => $pid;
	my $execdir = $perlvar{'lonDaemons'};


=head1 Terminate
Terminate the system.


sub Terminate {
    &Log("CRITICAL", "Asked to kill children.. first be nice...");
    #  By now they really should all be dead.. but just in case 
    #  send them all SIGKILL's after a bit of waiting:

    &Log("CRITICAL", "Now kill children nasty");
    Log("CRITICAL","Master process exiting");
    exit 0;


=head1 Theory

The event class is used to build this as a single process with an
event driven model.  The following events are handled:

=item UNIX Socket connection Received

=item Request data arrives on UNIX data transfer socket.

=item lond connection becomes writable.

=item timer fires at 1 second intervals.

All sockets are run in non-blocking mode.  Timeouts managed by the timer
handler prevents hung connections.

Key data structures:

=item RequestQueue

A queue of requests received from UNIX sockets that are
waiting for a chance to be forwarded on a lond connection socket.

=item ActiveConnections

A hash of lond connections that have transactions in process that are
available to be timed out.

=item ActiveTransactions

A hash indexed by lond connections that contain the client reply
socket for each connection that has an active transaction on it.

=item IdleConnections

A hash of lond connections that have no work to do.  These connections
can be closed if they are idle for a long enough time.


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