--- AnyEvent-MP/MP.pm 2009/08/05 19:55:58 1.31 +++ AnyEvent-MP/MP.pm 2009/08/14 14:01:05 1.50 @@ -10,20 +10,44 @@ NODE # returns this node's noderef NODE $port # returns the noderef of the port + $SELF # receiving/own port id in rcv callbacks + + # initialise the node so it can send/receive messages + initialise_node; # -OR- + initialise_node "localhost:4040"; # -OR- + initialise_node "slave/", "localhost:4040" + + # ports are message endpoints + + # sending messages snd $port, type => data...; + snd $port, @msg; + snd @msg_with_first_element_being_a_port; - $SELF # receiving/own port id in rcv callbacks + # creating/using ports, the simple way + my $somple_port = port { my @msg = @_; 0 }; + + # creating/using ports, type matching + my $port = port; + rcv $port, ping => sub { snd $_[0], "pong"; 0 }; + rcv $port, pong => sub { warn "pong received\n"; 0 }; + + # create a port on another node + my $port = spawn $node, $initfunc, @initdata; + + # monitoring + mon $port, $cb->(@msg) # callback is invoked on death + mon $port, $otherport # kill otherport on abnormal death + mon $port, $otherport, @msg # send message on death - rcv $port, smartmatch => $cb->($port, @msg); +=head1 CURRENT STATUS - # 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 $_[2] is 3 + AnyEvent::MP - stable API, should work + AnyEvent::MP::Intro - outdated + AnyEvent::MP::Kernel - WIP + AnyEvent::MP::Transport - mostly stable + + stay tuned. =head1 DESCRIPTION @@ -37,7 +61,7 @@ At the moment, this module family is severly broken and underdocumented, so do not use. This was uploaded mainly to reserve the CPAN namespace - -stay tuned! The basic API should be finished, however. +stay tuned! =head1 CONCEPTS @@ -92,7 +116,7 @@ package AnyEvent::MP; -use AnyEvent::MP::Base; +use AnyEvent::MP::Kernel; use common::sense; @@ -102,11 +126,12 @@ use base "Exporter"; -our $VERSION = '0.1'; +our $VERSION = $AnyEvent::MP::Kernel::VERSION; + our @EXPORT = qw( NODE $NODE *SELF node_of _any_ resolve_node initialise_node - snd rcv mon kil reg psub + snd rcv mon kil reg psub spawn port ); @@ -125,10 +150,92 @@ to C or C, after which all local port identifiers become invalid. -=item $noderef = node_of $portid +=item $noderef = node_of $port Extracts and returns the noderef from a portid or a noderef. +=item initialise_node $noderef, $seednode, $seednode... + +=item initialise_node "slave/", $master, $master... + +Before a node can talk to other nodes on the network it has to initialise +itself - the minimum a node needs to know is it's own name, and optionally +it should know the noderefs of some other nodes in the network. + +This function initialises a node - it must be called exactly once (or +never) before calling other AnyEvent::MP functions. + +All arguments (optionally except for the first) are noderefs, which can be +either resolved or unresolved. + +The first argument will be looked up in the configuration database first +(if it is C then the current nodename will be used instead) to find +the relevant configuration profile (see L). If none is found then +the default configuration is used. The configuration supplies additional +seed/master nodes and can override the actual noderef. + +There are two types of networked nodes, public nodes and slave nodes: + +=over 4 + +=item public nodes + +For public nodes, C<$noderef> (supplied either directly to +C or indirectly via a profile or the nodename) must be a +noderef (possibly unresolved, in which case it will be resolved). + +After resolving, the node will bind itself on all endpoints and try to +connect to all additional C<$seednodes> that are specified. Seednodes are +optional and can be used to quickly bootstrap the node into an existing +network. + +=item slave nodes + +When the C<$noderef> (either as given or overriden by the config file) +is the special string C, then the node will become a slave +node. Slave nodes cannot be contacted from outside and will route most of +their traffic to the master node that they attach to. + +At least one additional noderef is required (either by specifying it +directly or because it is part of the configuration profile): The node +will try to connect to all of them and will become a slave attached to the +first node it can successfully connect to. + +=back + +This function will block until all nodes have been resolved and, for slave +nodes, until it has successfully established a connection to a master +server. + +Example: become a public node listening on the guessed noderef, or the one +specified via C for the current node. This should be the most common +form of invocation for "daemon"-type nodes. + + initialise_node; + +Example: become a slave node to any of the the seednodes specified via +C. This form is often used for commandline clients. + + initialise_node "slave/"; + +Example: become a slave node to any of the specified master servers. This +form is also often used for commandline clients. + + initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net"; + +Example: become a public node, and try to contact some well-known master +servers to become part of the network. + + initialise_node undef, "master1", "master2"; + +Example: become a public node listening on port C<4041>. + + initialise_node 4041; + +Example: become a public node, only visible on localhost port 4044. + + initialise_node "localhost:4044"; + =item $cv = resolve_node $noderef Takes an unresolved node reference that may contain hostnames and @@ -169,9 +276,9 @@ just export C<$SELF>, all the symbols called C are exported by this module, but only C<$SELF> is currently used. -=item snd $portid, type => @data +=item snd $port, type => @data -=item snd $portid, @msg +=item snd $port, @msg Send the given message to the given port ID, which can identify either a local or a remote port, and can be either a string or soemthignt hat @@ -191,40 +298,222 @@ that Storable can serialise and deserialise is allowed, and for the local node, anything can be passed. -=item kil $portid[, @reason] +=item $local_port = port -Kill the specified port with the given C<@reason>. +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. -If no C<@reason> is specified, then the port is killed "normally" (linked -ports will not be kileld, or even notified). +=item $local_port = port { my @msg = @_ } -Otherwise, linked ports get killed with the same reason (second form of -C, see below). +Creates a new local port, and returns its ID. Semantically the same as +creating a port and calling C on it. -Runtime errors while evaluating C callbacks or inside C blocks -will be reported as reason C<< die => $@ >>. +The block will be called for every message received on the port, with the +global variable C<$SELF> set to the port ID. Runtime errors will cause the +port to be Ced. The message will be passed as-is, no extra argument +(i.e. no port ID) will be passed to the callback. -Transport/communication errors are reported as C<< transport_error => -$message >>. +If you want to stop/destroy the port, simply C it: + + my $port = port { + my @msg = @_; + ... + kil $SELF; + }; + +=cut + +sub rcv($@); + +sub _kilme { + die "received message on port without callback"; +} + +sub port(;&) { + my $id = "$UNIQ." . $ID++; + my $port = "$NODE#$id"; + + rcv $port, shift || \&_kilme; + + $port +} -=item $guard = mon $portid, $cb->(@reason) +=item rcv $local_port, $callback->(@msg) -=item $guard = mon $portid, $otherport +Replaces the default callback on the specified port. There is no way to +remove the default callback: use C to disable it, or better +C the port when it is no longer needed. -=item $guard = mon $portid, $otherport, @msg +The global C<$SELF> (exported by this module) contains C<$port> while +executing the callback. Runtime errors during callback execution will +result in the port being Ced. -Monitor the given port and do something when the port is killed. +The default callback received all messages not matched by a more specific +C match. -In the first form, the callback is simply called with any number -of C<@reason> elements (no @reason means that the port was deleted +=item rcv $local_port, tag => $callback->(@msg_without_tag), ... + +Register callbacks to be called on messages starting with the given tag on +the given port (and return the port), or unregister it (when C<$callback> +is C<$undef>). + +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). + +Example: create a port and bind receivers on it in one go. + + my $port = rcv port, + msg1 => sub { ... }, + msg2 => sub { ... }, + ; + +Example: create a port, bind receivers and send it in a message elsewhere +in one go: + + snd $otherport, reply => + rcv port, + msg1 => sub { ... }, + ... + ; + +=cut + +sub rcv($@) { + my $port = shift; + my ($noderef, $portid) = split /#/, $port, 2; + + ($NODE{$noderef} || add_node $noderef) == $NODE{""} + or Carp::croak "$port: rcv can only be called on local ports, caught"; + + 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->[2] = 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{$port} || 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 +} + +=item $closure = psub { BLOCK } + +Remembers C<$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 +callbacks, i.e. runtime errors will cause the port to get Ced. + +This is useful when you register callbacks from C callbacks: + + 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"; + + sub { + local $SELF = $port; + + if (wantarray) { + my @res = eval { &$cb }; + _self_die if $@; + @res + } else { + my $res = eval { &$cb }; + _self_die if $@; + $res + } + } +} + +=item $guard = mon $port, $cb->(@reason) + +=item $guard = mon $port, $rcvport + +=item $guard = mon $port + +=item $guard = mon $port, $rcvport, @msg + +Monitor the given port and do something when the port is killed or +messages to it were lost, and optionally return a guard that can be used +to stop monitoring again. + +C effectively guarantees that, in the absence of hardware failures, +that after starting the monitor, either all messages sent to the port +will arrive, or the monitoring action will be invoked after possible +message loss has been detected. No messages will be lost "in between" +(after the first lost message no further messages will be received by the +port). After the monitoring action was invoked, further messages might get +delivered again. + +In the first form (callback), the callback is simply called with any +number of C<@reason> elements (no @reason means that the port was deleted "normally"). Note also that I<< the callback B never die >>, so use C if unsure. -In the second form, the other port will be C'ed with C<@reason>, iff -a @reason was specified, i.e. on "normal" kils nothing happens, while -under all other conditions, the other port is killed with the same reason. - -In the last form, a message of the form C<@msg, @reason> will be C. +In the second form (another port given), the other port (C<$rcvport>) +will be C'ed with C<@reason>, iff a @reason was specified, i.e. on +"normal" kils nothing happens, while under all other conditions, the other +port is killed with the same reason. + +The third form (kill self) is the same as the second form, except that +C<$rvport> defaults to C<$SELF>. + +In the last form (message), a message of the form C<@msg, @reason> will be +C. + +As a rule of thumb, monitoring requests should always monitor a port from +a local port (or 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 exmaple, when the connection +to the other node goes down permanently). When monitoring a port locally +these problems do not exist. Example: call a given callback when C<$port> is killed. @@ -232,9 +521,9 @@ Example: kill ourselves when C<$port> is killed abnormally. - mon $port, $self; + mon $port; -Example: send us a restart message another C<$port> is killed. +Example: send us a restart message when another C<$port> is killed. mon $port, $self => "restart"; @@ -245,7 +534,7 @@ my $node = $NODE{$noderef} || add_node $noderef; - my $cb = shift; + my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; unless (ref $cb) { if (@_) { @@ -286,233 +575,97 @@ sub mon_guard { my ($port, @refs) = @_; + #TODO: mon-less form? + mon $port, sub { 0 && @refs } } -=item lnk $port1, $port2 - -Link two ports. This is simply a shorthand for: - - mon $port1, $port2; - mon $port2, $port1; - -It means that if either one is killed abnormally, the other one gets -killed as well. - -=item $local_port = port +=item kil $port[, @reason] -Create a new local port object that can be used either as a pattern -matching port ("full port") or a single-callback port ("miniport"), -depending on how C callbacks are bound to the object. - -=item $portid = port { my @msg = @_; $finished } - -Creates a "mini port", that is, a very lightweight port without any -pattern matching behind it, and returns its ID. - -The block will be called for every message received on the port. When the -callback returns a true value its job is considered "done" and the port -will be destroyed. Otherwise it will stay alive. - -The message will be passed as-is, no extra argument (i.e. no port id) will -be passed to the callback. - -If you need the local port id in the callback, this works nicely: - - my $port; $port = port { - snd $otherport, reply => $port; - }; - -=cut - -sub port(;&) { - my $id = "$UNIQ." . $ID++; - my $port = "$NODE#$id"; - - if (@_) { - my $cb = shift; - $PORT{$id} = sub { - local $SELF = $port; - eval { - &$cb - and kil $id; - }; - _self_die if $@; - }; - } else { - my $self = bless { - id => "$NODE#$id", - }, "AnyEvent::MP::Port"; - - $PORT_DATA{$id} = $self; - $PORT{$id} = sub { - local $SELF = $port; - - eval { - for (@{ $self->{rc0}{$_[0]} }) { - $_ && &{$_->[0]} - && undef $_; - } - - for (@{ $self->{rcv}{$_[0]} }) { - $_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1] - && &{$_->[0]} - && undef $_; - } - - for (@{ $self->{any} }) { - $_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1] - && &{$_->[0]} - && undef $_; - } - }; - _self_die if $@; - }; - } - - $port -} +Kill the specified port with the given C<@reason>. -=item reg $portid, $name +If no C<@reason> is specified, then the port is killed "normally" (linked +ports will not be kileld, or even notified). -Registers the given port under the name C<$name>. If the name already -exists it is replaced. +Otherwise, linked ports get killed with the same reason (second form of +C, see below). -A port can only be registered under one well known name. +Runtime errors while evaluating C callbacks or inside C blocks +will be reported as reason C<< die => $@ >>. -A port automatically becomes unregistered when it is killed. +Transport/communication errors are reported as C<< transport_error => +$message >>. =cut -sub reg(@) { - my ($portid, $name) = @_; - - $REG{$name} = $portid; -} - -=item rcv $portid, $callback->(@msg) - -Replaces the callback on the specified miniport (or newly created port -object, see C). Full ports are configured with the following calls: - -=item rcv $portid, tagstring => $callback->(@msg), ... +=item $port = spawn $node, $initfunc[, @initdata] -=item rcv $portid, $smartmatch => $callback->(@msg), ... +Creates a port on the node C<$node> (which can also be a port ID, in which +case it's the node where that port resides). -=item rcv $portid, [$smartmatch...] => $callback->(@msg), ... +The port ID of the newly created port is return immediately, and it is +permissible to immediately start sending messages or monitor the port. -Register callbacks to be called on matching messages on the given port. +After the port has been created, the init function is +called. This function must be a fully-qualified function name +(e.g. C). To specify a function in the main +program, use C<::name>. -The callback has to return a true value when its work is done, after -which is will be removed, or a false value in which case it will stay -registered. +If the function doesn't exist, then the node tries to C +the package, then the package above the package and so on (e.g. +C, C, C) until the function +exists or it runs out of package names. -The global C<$SELF> (exported by this module) contains C<$portid> while -executing the callback. +The init function is then called with the newly-created port as context +object (C<$SELF>) and the C<@initdata> values as arguments. -Runtime errors wdurign callback execution will result in the port being -Ced. +A common idiom is to pass your own port, monitor the spawned port, and +in the init function, monitor the original port. This two-way monitoring +ensures that both ports get cleaned up when there is a problem. -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. +Example: spawn a chat server port on C<$othernode>. -Any element in the match that is specified as C<_any_> (a function -exported by this module) matches any single element of the message. - -While not required, it is highly recommended that the first matching -element is a string identifying the message. The one-string-only match is -also the most efficient match (by far). - -=cut - -sub rcv($@) { - my $portid = shift; - my ($noderef, $port) = split /#/, $port, 2; - - ($NODE{$noderef} || add_node $noderef) == $NODE{""} - or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught"; + # this node, executed from within a port context: + my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; + mon $server; - my $self = $PORT_DATA{$port} - or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught"; + # init function on C<$othernode> + sub connect { + my ($srcport) = @_; - "AnyEvent::MP::Port" eq ref $self - or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught"; + mon $srcport; - while (@_) { - my ($match, $cb) = splice @_, 0, 2; - - if (!ref $match) { - push @{ $self->{rc0}{$match} }, [$cb]; - } elsif (("ARRAY" eq ref $match && !ref $match->[0])) { - my ($type, @match) = @$match; - @match - ? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match] - : push @{ $self->{rc0}{$match->[0]} }, [$cb]; - } else { - push @{ $self->{any} }, [$cb, $match]; - } - } - - $portid -} - -=item $closure = psub { BLOCK } - -Remembers C<$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 -callbacks, i.e. runtime errors will cause the port to get Ced. - -This is useful when you register callbacks from C callbacks: - - rcv delayed_reply => sub { - my ($delay, @reply) = @_; - my $timer = AE::timer $delay, 0, psub { - snd @reply, $SELF; + rcv $SELF, sub { + ... }; - }; + } =cut -sub psub(&) { - my $cb = shift; - - my $port = $SELF - or Carp::croak "psub can only be called from within rcv or psub callbacks, not"; - - sub { - local $SELF = $port; - - if (wantarray) { - my @res = eval { &$cb }; - _self_die if $@; - @res - } else { - my $res = eval { &$cb }; - _self_die if $@; - $res - } - } +sub _spawn { + my $port = shift; + my $init = shift; + + local $SELF = "$NODE#$port"; + eval { + &{ load_func $init } + }; + _self_die if $@; } -=back - -=head1 FUNCTIONS FOR NODES - -=over 4 - -=item become_public $noderef +sub spawn(@) { + my ($noderef, undef) = split /#/, shift, 2; -Tells the node to become a public node, i.e. reachable from other nodes. + my $id = "$RUNIQ." . $ID++; -The first argument is the (unresolved) node reference of the local node -(if missing then the empty string is used). + $_[0] =~ /::/ + or Carp::croak "spawn init function must be a fully-qualified name, caught"; -It is quite common to not specify anything, in which case the local node -tries to listen on the default port, or to only specify a port number, in -which case AnyEvent::MP tries to guess the local addresses. + ($NODE{$noderef} || add_node $noderef) + ->send (["", "AnyEvent::MP::_spawn" => $id, @_]); -=cut + "$noderef#$id" +} =back @@ -564,15 +717,15 @@ =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 +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 + 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: @@ -593,11 +746,11 @@ needs a queue. AEMP is event based, queuing messages would serve no useful purpose. -(But see L for a more erlang-like process model on top of AEMP). +(But see L for a more Erlang-like process model on top of AEMP). =item * Erlang sends are synchronous, AEMP sends are asynchronous. -Sending messages in erlang is synchronous and blocks the process. AEMP +Sending messages in Erlang is synchronous and blocks the process. AEMP sends are immediate, connection establishment is handled in the background. @@ -610,10 +763,10 @@ AEMP guarantees correct ordering, and the guarantee that there are no holes in the message sequence. -=item * In erlang, processes can be declared dead and later be found to be +=item * In Erlang, processes can be declared dead and later be found to be alive. -In erlang it can happen that a monitored process is declared dead and +In Erlang it can happen that a monitored process is declared dead and linked processes get killed, but later it turns out that the process is still alive - and can receive messages. @@ -623,7 +776,7 @@ =item * Erlang can send messages to the wrong port, AEMP does not. -In erlang it is quite possible that a node that restarts reuses a process +In Erlang it is quite possible that a node that restarts reuses a process ID known to other nodes for a completely different process, causing messages destined for that process to end up in an unrelated process. @@ -639,7 +792,7 @@ =item * The AEMP protocol is optimised for both text-based and binary communications. -The AEMP protocol, unlike the erlang protocol, supports both +The AEMP protocol, unlike the Erlang protocol, supports both language-independent text-only protocols (good for debugging) and binary, language-specific serialisers (e.g. Storable). @@ -647,6 +800,63 @@ with a minimum of work while gracefully degrading fucntionality to make the protocol simple. +=item * AEMP has more flexible monitoring options than Erlang. + +In Erlang, you can chose to receive I exit signals as messages +or I, there is no in-between, so monitoring single 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-process basis. + +=item * Erlang tries to hide remote/local connections, AEMP does not. + +Monitoring in Erlang is not an indicator of process death/crashes, +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 the you, and you monitor +the remote port. Since both monitors are local to the node, they are much +more reliable. + +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 ports and noderefs, why not objects? + +We considered "objects", but found that the actual number of methods +thatc an be called are very low. Since port IDs and noderefs travel over +the network frequently, the serialising/deserialising would add lots of +overhead, as well as having to keep a proxy object. + +Strings can easily be printed, easily serialised etc. and need no special +procedures to be "valid". + +And a a miniport consists of a single closure stored in a global hash - it +can't become much cheaper. + +=item Why favour JSON, why not 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. + +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 gains: 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 SEE ALSO