--- AnyEvent-MP/MP.pm	2009/08/01 07:44:02	1.5
+++ AnyEvent-MP/MP.pm	2012/03/23 21:16:25	1.144
@@ -1,33 +1,76 @@
 =head1 NAME
 
-AnyEvent::MP - multi-processing/message-passing framework
+AnyEvent::MP - erlang-style multi-processing/message-passing framework
 
 =head1 SYNOPSIS
 
    use AnyEvent::MP;
 
-   NODE    # returns this node identifier
-   $NODE   # contains this node identifier
+   $NODE      # contains this node's node ID
+   NODE       # returns this node's node ID
 
+   $SELF      # receiving/own port id in rcv callbacks
+
+   # initialise the node so it can send/receive messages
+   configure;
+
+   # ports are message destinations
+
+   # sending messages
    snd $port, type => data...;
+   snd $port, @msg;
+   snd @msg_with_first_element_being_a_port;
+
+   # creating/using ports, the simple way
+   my $simple_port = port { my @msg = @_ };
+
+   # creating/using ports, tagged message matching
+   my $port = port;
+   rcv $port, ping => sub { snd $_[0], "pong" };
+   rcv $port, pong => sub { warn "pong received\n" };
+
+   # create a port on another node
+   my $port = spawn $node, $initfunc, @initdata;
+
+   # destroy a port again
+   kil $port;  # "normal" kill
+   kil $port, my_error => "everything is broken"; # error kill
+
+   # monitoring
+   mon $port, $cb->(@msg)      # callback is invoked on death
+   mon $port, $localport       # kill localport on abnormal death
+   mon $port, $localport, @msg # send message on death
+
+   # temporarily execute code in port context
+   peval $port, sub { die "kill the port!" };
+
+   # execute callbacks in $SELF port context
+   my $timer = AE::timer 1, 0, psub {
+      die "kill the port, delayed";
+   };
 
-   rcv $port, smartmatch => $cb->($port, @msg);
+   # distributed database - modification
+   db_set $family => $subkey [=> $value]  # add a subkey
+   db_del $family => $subkey...           # delete one or more subkeys
+   db_reg $family => $port [=> $value]    # register a port
+
+   # distributed database - queries
+   db_family $family => $cb->(\%familyhash)
+   db_keys   $family => $cb->(\@keys)
+   db_values $family => $cb->(\@values)
 
-   # examples:
-   rcv $port2, ping => sub { snd $_[0], "pong"; 0 };
-   rcv $port1, pong => sub { warn "pong received\n" };
-   snd $port2, ping => $port1;
-
-   # more, smarter, matches (_any_ is exported by this module)
-   rcv $port, [child_died => $pid] => sub { ...
-   rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
+   # distributed database - monitoring a family
+   db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
 
 =head1 DESCRIPTION
 
 This module (-family) implements a simple message passing framework.
 
 Despite its simplicity, you can securely message other processes running
-on the same or other hosts.
+on the same or other hosts, and you can supervise entities remotely.
+
+For an introduction to this module family, see the L<AnyEvent::MP::Intro>
+manual page and the examples under F<eg/>.
 
 =head1 CONCEPTS
 
@@ -35,30 +78,100 @@
 
 =item port
 
-A port is something you can send messages to with the C<snd> function, and
-you can register C<rcv> handlers with. All C<rcv> handlers will receive
-messages they match, messages will not be queued.
+Not to be confused with a TCP port, a "port" is something you can send
+messages to (with the C<snd> function).
+
+Ports allow you to register C<rcv> handlers that can match all or just
+some messages. Messages send to ports will not be queued, regardless of
+anything was listening for them or not.
+
+Ports are represented by (printable) strings called "port IDs".
 
-=item port id - C<noderef#portname>
+=item port ID - C<nodeid#portname>
 
-A port id is always the noderef, a hash-mark (C<#>) as separator, followed
-by a port name (a printable string of unspecified format).
+A port ID is the concatenation of a node ID, a hash-mark (C<#>)
+as separator, and a port name (a printable string of unspecified
+format created by AnyEvent::MP).
 
 =item node
 
-A node is a single process containing at least one port - the node
-port. You can send messages to node ports to let them create new ports,
-among other things.
-
-Initially, nodes are either private (single-process only) or hidden
-(connected to a master node only). Only when they epxlicitly "become
-public" can you send them messages from unrelated other nodes.
-
-=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>
-
-A noderef is a string that either uniquely identifies a given node (for
-private and hidden nodes), or contains a recipe on how to reach a given
-node (for public nodes).
+A node is a single process containing at least one port - the node port,
+which enables nodes to manage each other remotely, and to create new
+ports.
+
+Nodes are either public (have one or more listening ports) or private
+(no listening ports). Private nodes cannot talk to other private nodes
+currently, but all nodes can talk to public nodes.
+
+Nodes is represented by (printable) strings called "node IDs".
+
+=item node ID - C<[A-Za-z0-9_\-.:]*>
+
+A node ID is a string that uniquely identifies the node within a
+network. Depending on the configuration used, node IDs can look like a
+hostname, a hostname and a port, or a random string. AnyEvent::MP itself
+doesn't interpret node IDs in any way except to uniquely identify a node.
+
+=item binds - C<ip:port>
+
+Nodes can only talk to each other by creating some kind of connection to
+each other. To do this, nodes should listen on one or more local transport
+endpoints - binds.
+
+Currently, only standard C<ip:port> specifications can be used, which
+specify TCP ports to listen on. So a bind is basically just a tcp socket
+in listening mode thta accepts conenctions form other nodes.
+
+=item seed nodes
+
+When a node starts, it knows nothing about the network it is in - it
+needs to connect to at least one other node that is already in the
+network. These other nodes are called "seed nodes".
+
+Seed nodes themselves are not special - they are seed nodes only because
+some other node I<uses> them as such, but any node can be used as seed
+node for other nodes, and eahc node cna use a different set of seed nodes.
+
+In addition to discovering the network, seed nodes are also used to
+maintain the network - all nodes using the same seed node form are part of
+the same network. If a network is split into multiple subnets because e.g.
+the network link between the parts goes down, then using the same seed
+nodes for all nodes ensures that eventually the subnets get merged again.
+
+Seed nodes are expected to be long-running, and at least one seed node
+should always be available. They should also be relatively responsive - a
+seed node that blocks for long periods will slow down everybody else.
+
+For small networks, it's best if every node uses the same set of seed
+nodes. For large networks, it can be useful to specify "regional" seed
+nodes for most nodes in an area, and use all seed nodes as seed nodes for
+each other. What's important is that all seed nodes connections form a
+complete graph, so that the network cannot split into separate subnets
+forever.
+
+Seed nodes are represented by seed IDs.
+
+=item seed IDs - C<host:port>
+
+Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
+TCP port) of nodes that should be used as seed nodes.
+
+=item global nodes
+
+An AEMP network needs a discovery service - nodes need to know how to
+connect to other nodes they only know by name. In addition, AEMP offers a
+distributed "group database", which maps group names to a list of strings
+- for example, to register worker ports.
+
+A network needs at least one global node to work, and allows every node to
+be a global node.
+
+Any node that loads the L<AnyEvent::MP::Global> module becomes a global
+node and tries to keep connections to all other nodes. So while it can
+make sense to make every node "global" in small networks, it usually makes
+sense to only make seed nodes into global nodes in large networks (nodes
+keep connections to seed nodes and global nodes, so makign them the same
+reduces overhead).
 
 =back
 
@@ -70,373 +183,1220 @@
 
 package AnyEvent::MP;
 
-use AnyEvent::MP::Util ();
-use AnyEvent::MP::Node;
-use AnyEvent::MP::Transport;
+use AnyEvent::MP::Config ();
+use AnyEvent::MP::Kernel;
+use AnyEvent::MP::Kernel qw(
+   %NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID
+   add_node load_func
+
+   NODE $NODE
+   configure
+   node_of port_is_local
+   snd kil
+   db_set db_del
+   db_mon db_family db_keys db_values
+);
 
-use utf8;
 use common::sense;
 
 use Carp ();
 
-use AE ();
+use AnyEvent ();
+use Guard ();
 
 use base "Exporter";
 
-our $VERSION = '0.0';
-our @EXPORT = qw(NODE $NODE $PORT snd rcv _any_);
+our $VERSION = $AnyEvent::MP::Config::VERSION;
 
-our $DEFAULT_SECRET;
-our $DEFAULT_PORT = "4040";
+our @EXPORT = qw(
+   NODE $NODE
+   configure
+   node_of port_is_local
+   snd kil
+   db_set db_del
+   db_mon db_family db_keys db_values
+
+   *SELF
+
+   port rcv mon mon_guard psub peval spawn cal
+   db_set db_del db_reg
+   db_mon db_family db_keys db_values
+
+   after
+);
+
+our $SELF;
+
+sub _self_die() {
+   my $msg = $@;
+   $msg =~ s/\n+$// unless ref $msg;
+   kil $SELF, die => $msg;
+}
 
-our $CONNECT_INTERVAL =  5; # new connect every 5s, at least
-our $CONNECT_TIMEOUT  = 30; # includes handshake
+=item $thisnode = NODE / $NODE
 
-sub default_secret {
-   unless (defined $DEFAULT_SECRET) {
-      if (open my $fh, "<$ENV{HOME}/.aemp-secret") {
-         sysread $fh, $DEFAULT_SECRET, -s $fh;
-      } else {
-         $DEFAULT_SECRET = AnyEvent::MP::Util::nonce 32;
-      }
-   }
+The C<NODE> function returns, and the C<$NODE> variable contains, the node
+ID of the node running in the current process. This value is initialised by
+a call to C<configure>.
 
-   $DEFAULT_SECRET
-}
+=item $nodeid = node_of $port
 
-=item NODE / $NODE
+Extracts and returns the node ID from a port ID or a node ID.
 
-The C<NODE ()> function and the C<$NODE> variable contain the noderef of
-the local node. The value is initialised by a call to C<become_public> or
-C<become_slave>, after which all local port identifiers become invalid.
+=item $is_local = port_is_local $port
 
-=cut
+Returns true iff the port is a local port.
 
-our $UNIQ = sprintf "%x.%x", $$, time; # per-process/node unique cookie
-our $PUBLIC = 0;
-our $NODE;
-our $PORT;
+=item configure $profile, key => value...
 
-our %NODE; # node id to transport mapping, or "undef", for local node
-our %PORT; # local ports
-our %LISTENER; # local transports
+=item configure key => value...
 
-sub NODE() { $NODE }
+Before a node can talk to other nodes on the network (i.e. enter
+"distributed mode") it has to configure itself - the minimum a node needs
+to know is its own name, and optionally it should know the addresses of
+some other nodes in the network to discover other nodes.
 
-{
-   use POSIX ();
-   my $nodename = (POSIX::uname)[1];
-   $NODE = "$$\@$nodename";
-}
+This function configures a node - it must be called exactly once (or
+never) before calling other AnyEvent::MP functions.
 
-sub _ANY_() { 1 }
-sub _any_() { \&_ANY_ }
+The key/value pairs are basically the same ones as documented for the
+F<aemp> command line utility (sans the set/del prefix), with these additions:
 
-sub add_node {
-   my ($noderef) = @_;
+=over 4
 
-   return $NODE{$noderef}
-      if exists $NODE{$noderef};
+=item norc => $boolean (default false)
 
-   for (split /,/, $noderef) {
-      return $NODE{$noderef} = $NODE{$_}
-         if exists $NODE{$_};
-   }
+If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
+be consulted - all configuraiton options must be specified in the
+C<configure> call.
 
-   # for indirect sends, use a different class
-   my $node = new AnyEvent::MP::Node::Direct $noderef;
+=item force => $boolean (default false)
 
-   $NODE{$_} = $node
-      for $noderef, split /,/, $noderef;
+IF true, then the values specified in the C<configure> will take
+precedence over any values configured via the rc file. The default is for
+the rc file to override any options specified in the program.
 
-   $node
-}
+=back
 
-=item snd $portid, type => @data
+=over 4
 
-=item snd $portid, @msg
+=item step 1, gathering configuration from profiles
 
-Send the given message to the given port ID, which can identify either a
-local or a remote port.
+The function first looks up a profile in the aemp configuration (see the
+L<aemp> commandline utility). The profile name can be specified via the
+named C<profile> parameter or can simply be the first parameter). If it is
+missing, then the nodename (F<uname -n>) will be used as profile name.
+
+The profile data is then gathered as follows:
+
+First, all remaining key => value pairs (all of which are conveniently
+undocumented at the moment) will be interpreted as configuration
+data. Then they will be overwritten by any values specified in the global
+default configuration (see the F<aemp> utility), then the chain of
+profiles chosen by the profile name (and any C<parent> attributes).
+
+That means that the values specified in the profile have highest priority
+and the values specified directly via C<configure> have lowest priority,
+and can only be used to specify defaults.
+
+If the profile specifies a node ID, then this will become the node ID of
+this process. If not, then the profile name will be used as node ID, with
+a unique randoms tring (C</%u>) appended.
+
+The node ID can contain some C<%> sequences that are expanded: C<%n>
+is expanded to the local nodename, C<%u> is replaced by a random
+strign to make the node unique. For example, the F<aemp> commandline
+utility uses C<aemp/%n/%u> as nodename, which might expand to
+C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
+
+=item step 2, bind listener sockets
+
+The next step is to look up the binds in the profile, followed by binding
+aemp protocol listeners on all binds specified (it is possible and valid
+to have no binds, meaning that the node cannot be contacted form the
+outside. This means the node cannot talk to other nodes that also have no
+binds, but it can still talk to all "normal" nodes).
+
+If the profile does not specify a binds list, then a default of C<*> is
+used, meaning the node will bind on a dynamically-assigned port on every
+local IP address it finds.
+
+=item step 3, connect to seed nodes
+
+As the last step, the seed ID list from the profile is passed to the
+L<AnyEvent::MP::Global> module, which will then use it to keep
+connectivity with at least one node at any point in time.
 
-While the message can be about anything, it is highly recommended to use
-a constant string as first element.
+=back
 
-The message data effectively becomes read-only after a call to this
-function: modifying any argument is not allowed and can cause many
-problems.
+Example: become a distributed node using the local node name as profile.
+This should be the most common form of invocation for "daemon"-type nodes.
+
+   configure
+
+Example: become a semi-anonymous node. This form is often used for
+commandline clients.
+
+   configure nodeid => "myscript/%n/%u";
+
+Example: configure a node using a profile called seed, which is suitable
+for a seed node as it binds on all local addresses on a fixed port (4040,
+customary for aemp).
+
+   # use the aemp commandline utility
+   # aemp profile seed binds '*:4040'
+
+   # then use it
+   configure profile => "seed";
+
+   # or simply use aemp from the shell again:
+   # aemp run profile seed
+
+   # or provide a nicer-to-remember nodeid
+   # aemp run profile seed nodeid "$(hostname)"
+
+=item $SELF
+
+Contains the current port id while executing C<rcv> callbacks or C<psub>
+blocks.
+
+=item *SELF, SELF, %SELF, @SELF...
+
+Due to some quirks in how perl exports variables, it is impossible to
+just export C<$SELF>, all the symbols named C<SELF> are exported by this
+module, but only C<$SELF> is currently used.
+
+=item snd $port, type => @data
+
+=item snd $port, @msg
+
+Send the given message to the given port, which can identify either a
+local or a remote port, and must be a port ID.
+
+While the message can be almost anything, it is highly recommended to
+use a string as first element (a port ID, or some word that indicates a
+request type etc.) and to consist if only simple perl values (scalars,
+arrays, hashes) - if you think you need to pass an object, think again.
+
+The message data logically becomes read-only after a call to this
+function: modifying any argument (or values referenced by them) is
+forbidden, as there can be considerable time between the call to C<snd>
+and the time the message is actually being serialised - in fact, it might
+never be copied as within the same process it is simply handed to the
+receiving port.
 
 The type of data you can transfer depends on the transport protocol: when
 JSON is used, then only strings, numbers and arrays and hashes consisting
 of those are allowed (no objects). When Storable is used, then anything
 that Storable can serialise and deserialise is allowed, and for the local
-node, anything can be passed.
+node, anything can be passed. Best rely only on the common denominator of
+these.
+
+=item $local_port = port
+
+Create a new local port object and returns its port ID. Initially it has
+no callbacks set and will throw an error when it receives messages.
+
+=item $local_port = port { my @msg = @_ }
+
+Creates a new local port, and returns its ID. Semantically the same as
+creating a port and calling C<rcv $port, $callback> on it.
+
+The block will be called for every message received on the port, with the
+global variable C<$SELF> set to the port ID. Runtime errors will cause the
+port to be C<kil>ed. The message will be passed as-is, no extra argument
+(i.e. no port ID) will be passed to the callback.
+
+If you want to stop/destroy the port, simply C<kil> it:
+
+   my $port = port {
+      my @msg = @_;
+      ...
+      kil $SELF;
+   };
 
 =cut
 
-sub snd(@) {
-   my ($noderef, $port) = split /#/, shift, 2;
+sub rcv($@);
+
+my $KILME = sub {
+   (my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
+   kil $SELF, unhandled_message => "no callback found for message '$tag'";
+};
+
+sub port(;&) {
+   my $id = $UNIQ . ++$ID;
+   my $port = "$NODE#$id";
 
-   add_node $noderef
-      unless exists $NODE{$noderef};
+   rcv $port, shift || $KILME;
 
-   $NODE{$noderef}->send (["$port", [@_]]);
+   $port
 }
 
-=item rcv $portid, type => $callback->(@msg)
+=item rcv $local_port, $callback->(@msg)
+
+Replaces the default callback on the specified port. There is no way to
+remove the default callback: use C<sub { }> to disable it, or better
+C<kil> the port when it is no longer needed.
+
+The global C<$SELF> (exported by this module) contains C<$port> while
+executing the callback. Runtime errors during callback execution will
+result in the port being C<kil>ed.
+
+The default callback receives all messages not matched by a more specific
+C<tag> match.
 
-=item rcv $portid, $smartmatch => $callback->(@msg)
+=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
 
-=item rcv $portid, [$smartmatch...] => $callback->(@msg)
+Register (or replace) callbacks to be called on messages starting with the
+given tag on the given port (and return the port), or unregister it (when
+C<$callback> is C<$undef> or missing). There can only be one callback
+registered for each tag.
 
-Register a callback on the port identified by C<$portid>, which I<must> be
-a local port.
+The original message will be passed to the callback, after the first
+element (the tag) has been removed. The callback will use the same
+environment as the default callback (see above).
 
-The callback has to return a true value when its work is done, after
-which is will be removed, or a false value in which case it will stay
-registered.
+Example: create a port and bind receivers on it in one go.
 
-If the match is an array reference, then it will be matched against the
-first elements of the message, otherwise only the first element is being
-matched.
+  my $port = rcv port,
+     msg1 => sub { ... },
+     msg2 => sub { ... },
+  ;
 
-Any element in the match that is specified as C<_any_> (a function
-exported by this module) matches any single element of the message.
+Example: create a port, bind receivers and send it in a message elsewhere
+in one go:
 
-While not required, it is highly recommended that the first matching
-element is a string identifying the message. The one-string-only match is
-also the most efficient match (by far).
+   snd $otherport, reply =>
+      rcv port,
+         msg1 => sub { ... },
+         ...
+   ;
+
+Example: temporarily register a rcv callback for a tag matching some port
+(e.g. for an rpc reply) and unregister it after a message was received.
+
+   rcv $port, $otherport => sub {
+      my @reply = @_;
+
+      rcv $SELF, $otherport;
+   };
 
 =cut
 
 sub rcv($@) {
-   my ($port, $match, $cb) = @_;
+   my $port = shift;
+   my ($nodeid, $portid) = split /#/, $port, 2;
 
-   my $port = $PORT{$port}
-      or do {
-         my ($noderef, $lport) = split /#/, $port;
-         "AnyEvent::MP::Node::Self" eq ref $NODE{$noderef}
-            or Carp::croak "$port: can only rcv on local ports";
-
-         $PORT{$lport}
-            or Carp::croak "$port: port does not exist";
-            
-         $PORT{$port} = $PORT{$lport} # also return
-      };
+   $nodeid eq $NODE
+      or Carp::croak "$port: rcv can only be called on local ports, caught";
 
-   if (!ref $match) {
-      push @{ $port->{rc0}{$match}      }, [$cb];
-   } elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
-      my ($type, @match) = @$match;
-      @match
-         ? push @{ $port->{rcv}{$match->[0]} }, [$cb, \@match]
-         : push @{ $port->{rc0}{$match->[0]} }, [$cb];
-   } else {
-      push @{ $port->{any}              }, [$cb, $match];
+   while (@_) {
+      if (ref $_[0]) {
+         if (my $self = $PORT_DATA{$portid}) {
+            "AnyEvent::MP::Port" eq ref $self
+               or Carp::croak "$port: rcv can only be called on message matching ports, caught";
+
+            $self->[0] = shift;
+         } else {
+            my $cb = shift;
+            $PORT{$portid} = sub {
+               local $SELF = $port;
+               eval { &$cb }; _self_die if $@;
+            };
+         }
+      } elsif (defined $_[0]) {
+         my $self = $PORT_DATA{$portid} ||= do {
+            my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
+
+            $PORT{$portid} = sub {
+               local $SELF = $port;
+
+               if (my $cb = $self->[1]{$_[0]}) {
+                  shift;
+                  eval { &$cb }; _self_die if $@;
+               } else {
+                  &{ $self->[0] };
+               }
+            };
+
+            $self
+         };
+
+         "AnyEvent::MP::Port" eq ref $self
+            or Carp::croak "$port: rcv can only be called on message matching ports, caught";
+
+         my ($tag, $cb) = splice @_, 0, 2;
+
+         if (defined $cb) {
+            $self->[1]{$tag} = $cb;
+         } else {
+            delete $self->[1]{$tag};
+         }
+      }
    }
+
+   $port
 }
 
-sub _inject {
-   my ($port, $msg) = @{+shift};
+=item peval $port, $coderef[, @args]
 
-   $port = $PORT{$port}
-      or return;
+Evaluates the given C<$codref> within the contetx of C<$port>, that is,
+when the code throews an exception the C<$port> will be killed.
 
-   @_ = @$msg;
+Any remaining args will be passed to the callback. Any return values will
+be returned to the caller.
 
-   for (@{ $port->{rc0}{$msg->[0]} }) {
-      $_ && &{$_->[0]}
-         && undef $_;
-   }
+This is useful when you temporarily want to execute code in the context of
+a port.
 
-   for (@{ $port->{rcv}{$msg->[0]} }) {
-      $_ && [@_[1..$#{$_->[1]}]] ~~ $_->[1]
-         && &{$_->[0]}
-         && undef $_;
-   }
+Example: create a port and run some initialisation code in it's context.
+
+   my $port = port { ... };
 
-   for (@{ $port->{any} }) {
-      $_ &&           [@_[0..$#{$_->[1]}]] ~~ $_->[1]
-         && &{$_->[0]}
-         && undef $_;
+   peval $port, sub {
+      init
+         or die "unable to init";
+   };
+
+=cut
+
+sub peval($$) {
+   local $SELF = shift;
+   my $cb = shift;
+
+   if (wantarray) {
+      my @res = eval { &$cb };
+      _self_die if $@;
+      @res
+   } else {
+      my $res = eval { &$cb };
+      _self_die if $@;
+      $res
    }
 }
 
-sub normalise_noderef($) {
-   my ($noderef) = @_;
+=item $closure = psub { BLOCK }
 
-   my $cv = AE::cv;
-   my @res;
+Remembers C<$SELF> and creates a closure out of the BLOCK. When the
+closure is executed, sets up the environment in the same way as in C<rcv>
+callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
 
-   $cv->begin (sub {
-      my %seen;
-      my @refs;
-      for (sort { $a->[0] <=> $b->[0] } @res) {
-         push @refs, $_->[1] unless $seen{$_->[1]}++
-      }
-      shift->send (join ",", @refs);
-   });
+The effect is basically as if it returned C<< sub { peval $SELF, sub {
+BLOCK }, @_ } >>.
 
-   $noderef = $DEFAULT_PORT unless length $noderef;
+This is useful when you register callbacks from C<rcv> callbacks:
 
-   my $idx;
-   for my $t (split /,/, $noderef) {
-      my $pri = ++$idx;
-      
-      #TODO: this should be outside normalise_noderef and in become_public
-      if ($t =~ /^\d*$/) {
-         my $nodename = (POSIX::uname)[1];
-
-         $cv->begin;
-         AnyEvent::Socket::resolve_sockaddr $nodename, $t || "aemp=$DEFAULT_PORT", "tcp", 0, undef, sub {
-            for (@_) {
-               my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
-               push @res, [
-                  $pri += 1e-5,
-                  AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
-               ];
-            }
-            $cv->end;
-         };
+   rcv delayed_reply => sub {
+      my ($delay, @reply) = @_;
+      my $timer = AE::timer $delay, 0, psub {
+         snd @reply, $SELF;
+      };
+   };
+
+=cut
+
+sub psub(&) {
+   my $cb = shift;
+
+   my $port = $SELF
+      or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
 
-#         my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;
-#
-#         for (@ipv4) {
-#            push @res, [
-#               $pri,
-#               AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t || $DEFAULT_PORT,
-#            ];
-#         }
+   sub {
+      local $SELF = $port;
+
+      if (wantarray) {
+         my @res = eval { &$cb };
+         _self_die if $@;
+         @res
       } else {
-         my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"
-            or Carp::croak "$t: unparsable transport descriptor";
+         my $res = eval { &$cb };
+         _self_die if $@;
+         $res
+      }
+   }
+}
 
-         $cv->begin;
-         AnyEvent::Socket::resolve_sockaddr $host, $port, "tcp", 0, undef, sub {
-            for (@_) {
-               my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
-               push @res, [
-                  $pri += 1e-5,
-                  AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
-               ];
-            }
-            $cv->end;
-         }
+=item $guard = mon $port, $rcvport          # kill $rcvport when $port dies
+
+=item $guard = mon $port                    # kill $SELF when $port dies
+
+=item $guard = mon $port, $cb->(@reason)    # call $cb when $port dies
+
+=item $guard = mon $port, $rcvport, @msg    # send a message when $port dies
+
+Monitor the given port and do something when the port is killed or
+messages to it were lost, and optionally return a guard that can be used
+to stop monitoring again.
+
+The first two forms distinguish between "normal" and "abnormal" kil's:
+
+In the first form (another port given), if the C<$port> is C<kil>'ed with
+a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
+same reason. That is, on "normal" kil's nothing happens, while under all
+other conditions, the other port is killed with the same reason.
+
+The second form (kill self) is the same as the first form, except that
+C<$rvport> defaults to C<$SELF>.
+
+The remaining forms don't distinguish between "normal" and "abnormal" kil's
+- it's up to the callback or receiver to check whether the C<@reason> is
+empty and act accordingly.
+
+In the third form (callback), the callback is simply called with any
+number of C<@reason> elements (empty @reason means that the port was deleted
+"normally"). Note also that I<< the callback B<must> never die >>, so use
+C<eval> if unsure.
+
+In the last form (message), a message of the form C<$rcvport, @msg,
+@reason> will be C<snd>.
+
+Monitoring-actions are one-shot: once messages are lost (and a monitoring
+alert was raised), they are removed and will not trigger again, even if it
+turns out that the port is still alive.
+
+As a rule of thumb, monitoring requests should always monitor a remote
+port locally (using a local C<$rcvport> or a callback). The reason is that
+kill messages might get lost, just like any other message. Another less
+obvious reason is that even monitoring requests can get lost (for example,
+when the connection to the other node goes down permanently). When
+monitoring a port locally these problems do not exist.
+
+C<mon> effectively guarantees that, in the absence of hardware failures,
+after starting the monitor, either all messages sent to the port will
+arrive, or the monitoring action will be invoked after possible message
+loss has been detected. No messages will be lost "in between" (after
+the first lost message no further messages will be received by the
+port). After the monitoring action was invoked, further messages might get
+delivered again.
+
+Inter-host-connection timeouts and monitoring depend on the transport
+used. The only transport currently implemented is TCP, and AnyEvent::MP
+relies on TCP to detect node-downs (this can take 10-15 minutes on a
+non-idle connection, and usually around two hours for idle connections).
+
+This means that monitoring is good for program errors and cleaning up
+stuff eventually, but they are no replacement for a timeout when you need
+to ensure some maximum latency.
+
+Example: call a given callback when C<$port> is killed.
+
+   mon $port, sub { warn "port died because of <@_>\n" };
+
+Example: kill ourselves when C<$port> is killed abnormally.
+
+   mon $port;
+
+Example: send us a restart message when another C<$port> is killed.
+
+   mon $port, $self => "restart";
+
+=cut
+
+sub mon {
+   my ($nodeid, $port) = split /#/, shift, 2;
+
+   my $node = $NODE{$nodeid} || add_node $nodeid;
+
+   my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
+
+   unless (ref $cb) {
+      if (@_) {
+         # send a kill info message
+         my (@msg) = ($cb, @_);
+         $cb = sub { snd @msg, @_ };
+      } else {
+         # simply kill other port
+         my $port = $cb;
+         $cb = sub { kil $port, @_ if @_ };
       }
    }
 
-   $cv->end;
+   $node->monitor ($port, $cb);
 
-   $cv
+   defined wantarray
+      and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
 }
 
-sub become_public {
-   return if $PUBLIC;
+=item $guard = mon_guard $port, $ref, $ref...
 
-   my $noderef = join ",", ref $_[0] ? @{+shift} : shift;
-   my @args = @_;
+Monitors the given C<$port> and keeps the passed references. When the port
+is killed, the references will be freed.
 
-   $NODE = (normalise_noderef $noderef)->recv;
+Optionally returns a guard that will stop the monitoring.
 
-   for my $t (split /,/, $NODE) {
-      $NODE{$t} = $NODE{""};
+This function is useful when you create e.g. timers or other watchers and
+want to free them when the port gets killed (note the use of C<psub>):
 
-      my ($host, $port) = AnyEvent::Socket::parse_hostport $t;
+  $port->rcv (start => sub {
+     my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
+        undef $timer if 0.9 < rand;
+     });
+  });
 
-      $LISTENER{$t} = AnyEvent::MP::Transport::mp_server $host, $port,
-         @args,
-         on_error   => sub {
-            die "on_error<@_>\n";#d#
-         },
-         on_connect => sub {
-            my ($tp) = @_;
+=cut
 
-            $NODE{$tp->{remote_id}} = $_[0];
-         },
-         sub {
-            my ($tp) = @_;
+sub mon_guard {
+   my ($port, @refs) = @_;
 
-            $NODE{"$tp->{peerhost}:$tp->{peerport}"} = $tp;
-         },
-      ;
-   }
+   #TODO: mon-less form?
 
-   $PUBLIC = 1;
+   mon $port, sub { 0 && @refs }
 }
 
-=back
+=item kil $port[, @reason]
 
-=head1 NODE MESSAGES
+Kill the specified port with the given C<@reason>.
 
-Nodes understand the following messages sent to them. Many of them take
-arguments called C<@reply>, which will simply be used to compose a reply
-message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
-the remaining arguments are simply the message data.
+If no C<@reason> is specified, then the port is killed "normally" -
+monitor callback will be invoked, but the kil will not cause linked ports
+(C<mon $mport, $lport> form) to get killed.
 
-=over 4
+If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
+form) get killed with the same reason.
+
+Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
+will be reported as reason C<< die => $@ >>.
+
+Transport/communication errors are reported as C<< transport_error =>
+$message >>.
+
+Common idioms:
+
+   # silently remove yourself, do not kill linked ports
+   kil $SELF;
+
+   # report a failure in some detail
+   kil $SELF, failure_mode_1 => "it failed with too high temperature";
+
+   # do not waste much time with killing, just die when something goes wrong
+   open my $fh, "<file"
+      or die "file: $!";
+
+=item $port = spawn $node, $initfunc[, @initdata]
+
+Creates a port on the node C<$node> (which can also be a port ID, in which
+case it's the node where that port resides).
+
+The port ID of the newly created port is returned immediately, and it is
+possible to immediately start sending messages or to monitor the port.
+
+After the port has been created, the init function is called on the remote
+node, in the same context as a C<rcv> callback. This function must be a
+fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
+specify a function in the main program, use C<::name>.
+
+If the function doesn't exist, then the node tries to C<require>
+the package, then the package above the package and so on (e.g.
+C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
+exists or it runs out of package names.
+
+The init function is then called with the newly-created port as context
+object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
+call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
+the port might not get created.
+
+A common idiom is to pass a local port, immediately monitor the spawned
+port, and in the remote init function, immediately monitor the passed
+local port. This two-way monitoring ensures that both ports get cleaned up
+when there is a problem.
+
+C<spawn> guarantees that the C<$initfunc> has no visible effects on the
+caller before C<spawn> returns (by delaying invocation when spawn is
+called for the local node).
+
+Example: spawn a chat server port on C<$othernode>.
+
+   # this node, executed from within a port context:
+   my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
+   mon $server;
+
+   # init function on C<$othernode>
+   sub connect {
+      my ($srcport) = @_;
+
+      mon $srcport;
+
+      rcv $SELF, sub {
+         ...
+      };
+   }
 
 =cut
 
-#############################################################################
-# self node code
+sub _spawn {
+   my $port = shift;
+   my $init = shift;
+
+   # rcv will create the actual port
+   local $SELF = "$NODE#$port";
+   eval {
+      &{ load_func $init }
+   };
+   _self_die if $@;
+}
+
+sub spawn(@) {
+   my ($nodeid, undef) = split /#/, shift, 2;
+
+   my $id = $RUNIQ . ++$ID;
 
-sub _new_port($) {
-   my ($name) = @_;
+   $_[0] =~ /::/
+      or Carp::croak "spawn init function must be a fully-qualified name, caught";
 
-   my ($noderef, $portname) = split /#/, $name;
+   snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
 
-   $PORT{$name} =
-   $PORT{$portname} = {
-      names => [$name, $portname],
+   "$nodeid#$id"
+}
+
+
+=item after $timeout, @msg
+
+=item after $timeout, $callback
+
+Either sends the given message, or call the given callback, after the
+specified number of seconds.
+
+This is simply a utility function that comes in handy at times - the
+AnyEvent::MP author is not convinced of the wisdom of having it, though,
+so it may go away in the future.
+
+=cut
+
+sub after($@) {
+   my ($timeout, @action) = @_;
+
+   my $t; $t = AE::timer $timeout, 0, sub {
+      undef $t;
+      ref $action[0]
+         ? $action[0]()
+         : snd @action;
    };
 }
 
-$NODE{""} = new AnyEvent::MP::Node::Self noderef => $NODE;
-_new_port "";
+#=item $cb2 = timeout $seconds, $cb[, @args]
+
+=item cal $port, @msg, $callback[, $timeout]
 
-=item relay => $port, @msg
+A simple form of RPC - sends a message to the given C<$port> with the
+given contents (C<@msg>), but adds a reply port to the message.
 
-Simply forwards the message to the given port.
+The reply port is created temporarily just for the purpose of receiving
+the reply, and will be C<kil>ed when no longer needed.
+
+A reply message sent to the port is passed to the C<$callback> as-is.
+
+If an optional time-out (in seconds) is given and it is not C<undef>,
+then the callback will be called without any arguments after the time-out
+elapsed and the port is C<kil>ed.
+
+If no time-out is given (or it is C<undef>), then the local port will
+monitor the remote port instead, so it eventually gets cleaned-up.
+
+Currently this function returns the temporary port, but this "feature"
+might go in future versions unless you can make a convincing case that
+this is indeed useful for something.
 
 =cut
 
-rcv "", relay => \&snd;
+sub cal(@) {
+   my $timeout = ref $_[-1] ? undef : pop;
+   my $cb = pop;
+
+   my $port = port {
+      undef $timeout;
+      kil $SELF;
+      &$cb;
+   };
+
+   if (defined $timeout) {
+      $timeout = AE::timer $timeout, 0, sub {
+         undef $timeout;
+         kil $port;
+         $cb->();
+      };
+   } else {
+      mon $_[0], sub {
+         kil $port;
+         $cb->();
+      };
+   }
+
+   push @_, $port;
+   &snd;
+
+   $port
+}
+
+=back
+
+=head1 DISTRIBUTED DATABASE
+
+AnyEvent::MP comes with a simple distributed database. The database will
+be mirrored asynchronously on all global nodes. Other nodes bind to one
+of the global nodes for their needs. Every node has a "local database"
+which contains all the values that are set locally. All local databases
+are merged together to form the global database, which can be queried.
+
+The database structure is that of a two-level hash - the database hash
+contains hashes which contain values, similarly to a perl hash of hashes,
+i.e.:
+
+  $DATABASE{$family}{$subkey} = $value
+
+The top level hash key is called "family", and the second-level hash key
+is called "subkey" or simply "key".
+
+The family must be alphanumeric, i.e. start with a letter and consist
+of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
+pretty much like Perl module names.
 
-=item eval => $string[ @reply]
+As the family namespace is global, it is recommended to prefix family names
+with the name of the application or module using it.
 
-Evaluates the given string. If C<@reply> is given, then a message of the
-form C<@reply, $@, @evalres> is sent.
+The subkeys must be non-empty strings, with no further restrictions.
+
+The values should preferably be strings, but other perl scalars should
+work as well (such as C<undef>, arrays and hashes).
+
+Every database entry is owned by one node - adding the same family/subkey
+combination on multiple nodes will not cause discomfort for AnyEvent::MP,
+but the result might be nondeterministic, i.e. the key might have
+different values on different nodes.
+
+Different subkeys in the same family can be owned by different nodes
+without problems, and in fact, this is the common method to create worker
+pools. For example, a worker port for image scaling might do this:
+
+   db_set my_image_scalers => $port;
+
+And clients looking for an image scaler will want to get the
+C<my_image_scalers> keys from time to time:
+
+   db_keys my_image_scalers => sub {
+      @ports = @{ $_[0] };
+   };
+
+Or better yet, they want to monitor the database family, so they always
+have a reasonable up-to-date copy:
+
+   db_mon my_image_scalers => sub {
+      @ports = keys %{ $_[0] };
+   };
 
-Example: crash another node.
+In general, you can set or delete single subkeys, but query and monitor
+whole families only.
 
-   snd $othernode, eval => "exit";
+If you feel the need to monitor or query a single subkey, try giving it
+it's own family.
+
+=over
+
+=item $guard = db_set $family => $subkey [=> $value]
+
+Sets (or replaces) a key to the database - if C<$value> is omitted,
+C<undef> is used instead.
+
+When called in non-void context, C<db_set> returns a guard that
+automatically calls C<db_del> when it is destroyed.
+
+=item db_del $family => $subkey...
+
+Deletes one or more subkeys from the database family.
+
+=item $guard = db_reg $family => $port => $value
+
+=item $guard = db_reg $family => $port
+
+=item $guard = db_reg $family
+
+Registers a port in the given family and optionally returns a guard to
+remove it.
+
+This function basically does the same as:
+
+   db_set $family => $port => $value
+
+Except that the port is monitored and automatically removed from the
+database family when it is kil'ed.
+
+If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
+C<$SELF> is used.
+
+This function is most useful to register a port in some port group (which
+is just another name for a database family), and have it removed when the
+port is gone. This works best when the port is a local port.
 
 =cut
 
-rcv "", eval => sub {
-   my (undef, $string, @reply) = @_;
-   my @res = eval $string;
-   snd @reply, "$@", @res if @reply;
-};
+sub db_reg($$;$) {
+   my $family = shift;
+   my $port = @_ ? shift : $SELF;
+
+   my $clr = sub { db_del $family => $port };
+   mon $port, $clr;
+
+   db_set $family => $port => $_[0];
+
+   defined wantarray
+      and &Guard::guard ($clr)
+}
+
+=item db_family $family => $cb->(\%familyhash)
 
-=item time => @reply
+Queries the named database C<$family> and call the callback with the
+family represented as a hash. You can keep and freely modify the hash.
 
-Replies the the current node time to C<@reply>.
+=item db_keys $family => $cb->(\@keys)
 
-Example: tell the current node to send the current time to C<$myport> in a
-C<timereply> message.
+Same as C<db_family>, except it only queries the family I<subkeys> and passes
+them as array reference to the callback.
 
-   snd $NODE, time => $myport, timereply => 1, 2;
-   # => snd $myport, timereply => 1, 2, <time>
+=item db_values $family => $cb->(\@values)
+
+Same as C<db_family>, except it only queries the family I<values> and passes them
+as array reference to the callback.
+
+=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
+
+Creates a monitor on the given database family. Each time a key is set
+or or is deleted the callback is called with a hash containing the
+database family and three lists of added, changed and deleted subkeys,
+respectively. If no keys have changed then the array reference might be
+C<undef> or even missing.
+
+If not called in void context, a guard object is returned that, when
+destroyed, stops the monitor.
+
+The family hash reference and the key arrays belong to AnyEvent::MP and
+B<must not be modified or stored> by the callback. When in doubt, make a
+copy.
+
+As soon as possible after the monitoring starts, the callback will be
+called with the intiial contents of the family, even if it is empty,
+i.e. there will always be a timely call to the callback with the current
+contents.
+
+It is possible that the callback is called with a change event even though
+the subkey is already present and the value has not changed.
+
+The monitoring stops when the guard object is destroyed.
+
+Example: on every change to the family "mygroup", print out all keys.
+
+   my $guard = db_mon mygroup => sub {
+      my ($family, $a, $c, $d) = @_;
+      print "mygroup members: ", (join " ", keys %$family), "\n";
+   };
+
+Exmaple: wait until the family "My::Module::workers" is non-empty.
+
+   my $guard; $guard = db_mon My::Module::workers => sub {
+      my ($family, $a, $c, $d) = @_;
+      return unless %$family;
+      undef $guard;
+      print "My::Module::workers now nonempty\n";
+   };
+
+Example: print all changes to the family "AnyRvent::Fantasy::Module".
+
+   my $guard = db_mon AnyRvent::Fantasy::Module => sub {
+      my ($family, $a, $c, $d) = @_;
+
+      print "+$_=$family->{$_}\n" for @$a;
+      print "*$_=$family->{$_}\n" for @$c;
+      print "-$_=$family->{$_}\n" for @$d;
+   };
 
 =cut
 
-rcv "", time  => sub { shift; snd @_, AE::time };
+=back
+
+=head1 AnyEvent::MP vs. Distributed Erlang
+
+AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
+== aemp node, Erlang process == aemp port), so many of the documents and
+programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
+sample:
+
+   http://www.erlang.se/doc/programming_rules.shtml
+   http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
+   http://erlang.org/download/erlang-book-part1.pdf      # chapters 5 and 6
+   http://erlang.org/download/armstrong_thesis_2003.pdf  # chapters 4 and 5
+
+Despite the similarities, there are also some important differences:
+
+=over 4
+
+=item * Node IDs are arbitrary strings in AEMP.
+
+Erlang relies on special naming and DNS to work everywhere in the same
+way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
+configuration or DNS), and possibly the addresses of some seed nodes, but
+will otherwise discover other nodes (and their IDs) itself.
+
+=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
+uses "local ports are like remote ports".
+
+The failure modes for local ports are quite different (runtime errors
+only) then for remote ports - when a local port dies, you I<know> it dies,
+when a connection to another node dies, you know nothing about the other
+port.
+
+Erlang pretends remote ports are as reliable as local ports, even when
+they are not.
+
+AEMP encourages a "treat remote ports differently" philosophy, with local
+ports being the special case/exception, where transport errors cannot
+occur.
+
+=item * Erlang uses processes and a mailbox, AEMP does not queue.
+
+Erlang uses processes that selectively receive messages out of order, and
+therefore needs a queue. AEMP is event based, queuing messages would serve
+no useful purpose. For the same reason the pattern-matching abilities
+of AnyEvent::MP are more limited, as there is little need to be able to
+filter messages without dequeuing them.
+
+This is not a philosophical difference, but simply stems from AnyEvent::MP
+being event-based, while Erlang is process-based.
+
+You cna have a look at L<Coro::MP> for a more Erlang-like process model on
+top of AEMP and Coro threads.
+
+=item * Erlang sends are synchronous, AEMP sends are asynchronous.
+
+Sending messages in Erlang is synchronous and blocks the process until
+a conenction has been established and the message sent (and so does not
+need a queue that can overflow). AEMP sends return immediately, connection
+establishment is handled in the background.
+
+=item * Erlang suffers from silent message loss, AEMP does not.
+
+Erlang implements few guarantees on messages delivery - messages can get
+lost without any of the processes realising it (i.e. you send messages a,
+b, and c, and the other side only receives messages a and c).
+
+AEMP guarantees (modulo hardware errors) correct ordering, and the
+guarantee that after one message is lost, all following ones sent to the
+same port are lost as well, until monitoring raises an error, so there are
+no silent "holes" in the message sequence.
+
+If you want your software to be very reliable, you have to cope with
+corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
+simply tries to work better in common error cases, such as when a network
+link goes down.
+
+=item * Erlang can send messages to the wrong port, AEMP does not.
+
+In Erlang it is quite likely that a node that restarts reuses an Erlang
+process ID known to other nodes for a completely different process,
+causing messages destined for that process to end up in an unrelated
+process.
+
+AEMP does not reuse port IDs, so old messages or old port IDs floating
+around in the network will not be sent to an unrelated port.
+
+=item * Erlang uses unprotected connections, AEMP uses secure
+authentication and can use TLS.
+
+AEMP can use a proven protocol - TLS - to protect connections and
+securely authenticate nodes.
+
+=item * The AEMP protocol is optimised for both text-based and binary
+communications.
+
+The AEMP protocol, unlike the Erlang protocol, supports both programming
+language independent text-only protocols (good for debugging), and binary,
+language-specific serialisers (e.g. Storable). By default, unless TLS is
+used, the protocol is actually completely text-based.
+
+It has also been carefully designed to be implementable in other languages
+with a minimum of work while gracefully degrading functionality to make the
+protocol simple.
+
+=item * AEMP has more flexible monitoring options than Erlang.
+
+In Erlang, you can chose to receive I<all> exit signals as messages or
+I<none>, there is no in-between, so monitoring single Erlang processes is
+difficult to implement.
+
+Monitoring in AEMP is more flexible than in Erlang, as one can choose
+between automatic kill, exit message or callback on a per-port basis.
+
+=item * Erlang tries to hide remote/local connections, AEMP does not.
+
+Monitoring in Erlang is not an indicator of process death/crashes, in the
+same way as linking is (except linking is unreliable in Erlang).
+
+In AEMP, you don't "look up" registered port names or send to named ports
+that might or might not be persistent. Instead, you normally spawn a port
+on the remote node. The init function monitors you, and you monitor the
+remote port. Since both monitors are local to the node, they are much more
+reliable (no need for C<spawn_link>).
+
+This also saves round-trips and avoids sending messages to the wrong port
+(hard to do in Erlang).
+
+=back
+
+=head1 RATIONALE
+
+=over 4
+
+=item Why strings for port and node IDs, why not objects?
+
+We considered "objects", but found that the actual number of methods
+that can be called are quite low. Since port and node IDs travel over
+the network frequently, the serialising/deserialising would add lots of
+overhead, as well as having to keep a proxy object everywhere.
+
+Strings can easily be printed, easily serialised etc. and need no special
+procedures to be "valid".
+
+And as a result, a port with just a default receiver consists of a single
+code reference stored in a global hash - it can't become much cheaper.
+
+=item Why favour JSON, why not a real serialising format such as Storable?
+
+In fact, any AnyEvent::MP node will happily accept Storable as framing
+format, but currently there is no way to make a node use Storable by
+default (although all nodes will accept it).
+
+The default framing protocol is JSON because a) JSON::XS is many times
+faster for small messages and b) most importantly, after years of
+experience we found that object serialisation is causing more problems
+than it solves: Just like function calls, objects simply do not travel
+easily over the network, mostly because they will always be a copy, so you
+always have to re-think your design.
+
+Keeping your messages simple, concentrating on data structures rather than
+objects, will keep your messages clean, tidy and efficient.
 
 =back
 
+=head1 PORTING FROM AnyEvent::MP VERSION 1.X
+
+AEMP version 2 has a few major incompatible changes compared to version 1:
+
+=over 4
+
+=item AnyEvent::MP::Global no longer has group management functions.
+
+At least not officially - the grp_* functions are still exported and might
+work, but they will be removed in some later release.
+
+AnyEvent::MP now comes with a distributed database that is more
+powerful. Its database families map closely to port groups, but the API
+has changed (the functions are also now exported by AnyEvent::MP). Here is
+a rough porting guide:
+
+  grp_reg $group, $port                      # old
+  db_reg $group, $port                       # new
+
+  $list = grp_get $group                     # old
+  db_keys $group, sub { my $list = shift }   # new
+
+  grp_mon $group, $cb->(\@ports, $add, $del) # old
+  db_mon $group, $cb->(\%ports, $add, $change, $del) # new
+
+C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
+no longer instant, because the local node might not have a copy of the
+group. You can either modify your code to allow for a callback, or use
+C<db_mon> to keep an updated copy of the group:
+
+  my $local_group_copy;
+  db_mon $group => sub { $local_group_copy = $_[0] };
+
+  # now "keys %$local_group_copy" always returns the most up-to-date
+  # list of ports in the group.
+
+C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
+passes a hash as first argument, and an extra C<$chg> argument that can be
+ignored:
+
+  db_mon $group => sub {
+     my ($ports, $add, $chg, $lde) = @_;
+     $ports = [keys %$ports];
+
+     # now $ports, $add and $del are the same as
+     # were originally passed by grp_mon.
+     ...
+  };
+
+=item Nodes not longer connect to all other nodes.
+
+In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
+module, which in turn would create connections to all other nodes in the
+network (helped by the seed nodes).
+
+In version 2.x, global nodes still connect to all other global nodes, but
+other nodes don't - now every node either is a global node itself, or
+attaches itself to another global node.
+
+If a node isn't a global node itself, then it attaches itself to one
+of its seed nodes. If that seed node isn't a global node yet, it will
+automatically be upgraded to a global node.
+
+So in many cases, nothing needs to be changed - one just has to make sure
+that all seed nodes are meshed together with the other seed nodes (as with
+AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
+achieved by specifying the same set of seed nodes for all nodes in the
+network.
+
+Not opening a connection to every other node is usually an advantage,
+except when you need the lower latency of an already established
+connection. To ensure a node establishes a connection to another node,
+you can monitor the node port (C<mon $node, ...>), which will attempt to
+create the connection (and notify you when the connection fails).
+
+=item Listener-less nodes (nodes without binds) are gone.
+
+And are not coming back, at least not in their old form. If no C<binds>
+are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
+
+There are vague plans to implement some form of routing domains, which
+might or might not bring back listener-less nodes, but don't count on it.
+
+The fact that most connections are now optional somewhat mitigates this,
+as a node can be effectively unreachable from the outside without any
+problems, as long as it isn't a global node and only reaches out to other
+nodes (as opposed to being contacted from other nodes).
+
+=item $AnyEvent::MP::Kernel::WARN has gone.
+
+AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
+uses this, and so should your programs.
+
+Every module now documents what kinds of messages it generates, with
+AnyEvent::MP acting as a catch all.
+
+On the positive side, this means that instead of setting
+C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
+much less to type.
+
+=back
+
+=head1 LOGGING
+
+AnyEvent::MP does not normally log anything by itself, but sinc eit is the
+root of the contetx hierarchy for AnyEvent::MP modules, it will receive
+all log messages by submodules.
+
 =head1 SEE ALSO
 
+L<AnyEvent::MP::Intro> - a gentle introduction.
+
+L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
+
+L<AnyEvent::MP::Global> - network maintenance and port groups, to find
+your applications.
+
+L<AnyEvent::MP::DataConn> - establish data connections between nodes.
+
+L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
+all nodes.
+
 L<AnyEvent>.
 
 =head1 AUTHOR