--- AnyEvent-MP/MP.pm 2009/08/27 21:29:37 1.63 +++ AnyEvent-MP/MP.pm 2012/03/08 21:37:51 1.129 @@ -1,21 +1,20 @@ =head1 NAME -AnyEvent::MP - multi-processing/message-passing framework +AnyEvent::MP - erlang-style multi-processing/message-passing framework =head1 SYNOPSIS use AnyEvent::MP; - $NODE # contains this node's noderef - NODE # returns this node's noderef - NODE $port # returns the noderef of the port + $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 - initialise_node; + configure; - # ports are message endpoints + # ports are message destinations # sending messages snd $port, type => data...; @@ -23,43 +22,50 @@ snd @msg_with_first_element_being_a_port; # creating/using ports, the simple way - my $simple_port = port { my @msg = @_; 0 }; + my $simple_port = port { my @msg = @_ }; # creating/using ports, tagged message matching my $port = port; - rcv $port, ping => sub { snd $_[0], "pong"; 0 }; - rcv $port, pong => sub { warn "pong received\n"; 0 }; + 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, $otherport # kill otherport on abnormal death - mon $port, $otherport, @msg # send message on death + mon $port, $localport # kill localport on abnormal death + mon $port, $localport, @msg # send message on death -=head1 CURRENT STATUS + # temporarily execute code in port context + peval $port, sub { die "kill the port!" }; - AnyEvent::MP - stable API, should work - AnyEvent::MP::Intro - outdated - AnyEvent::MP::Kernel - WIP - AnyEvent::MP::Transport - mostly stable + # execute callbacks in $SELF port context + my $timer = AE::timer 1, 0, psub { + die "kill the port, delayed"; + }; + +=head1 CURRENT STATUS - stay tuned. + bin/aemp - stable. + AnyEvent::MP - stable API, should work. + AnyEvent::MP::Intro - explains most concepts. + AnyEvent::MP::Kernel - mostly stable API. + AnyEvent::MP::Global - stable API. =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 -manual page. - -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! +manual page and the examples under F. =head1 CONCEPTS @@ -67,42 +73,100 @@ =item port -A port is something you can send messages to (with the C function). +Not to be confused with a TCP port, a "port" is something you can send +messages to (with the C function). Ports allow you to register C handlers that can match all or just -some messages. Messages will not be queued. +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 +=item port ID - C -A port ID is the concatenation of a noderef, a hash-mark (C<#>) as -separator, and a port name (a printable string of unspecified format). An -exception is the the node port, whose ID is identical to its node -reference. +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, -which provides nodes to manage each other remotely, and to create new +which enables nodes to manage each other remotely, and to create new ports. -Nodes are either private (single-process only), slaves (can only talk to -public nodes, but do not need an open port) or public nodes (connectable -from any other node). +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 + +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 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 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 node ID - C<[a-za-Z0-9_\-.:]+> +=item seed IDs - C -A node ID is a string that either simply identifies the node (for -private and slave nodes), or contains a recipe on how to reach a given -node (for public nodes). +Seed IDs are transport endpoint(s) (usually a hostname/IP address and a +TCP port) of nodes that should be used as seed nodes. -This recipe is simply a comma-separated list of C pairs (for -TCP/IP, other protocols might look different). +=item global nodes -Node references come in two flavours: resolved (containing only numerical -addresses) or unresolved (where hostnames are used instead of addresses). +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. -Before using an unresolved node reference in a message you first have to -resolve it. +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 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 @@ -114,23 +178,28 @@ package AnyEvent::MP; +use AnyEvent::MP::Config (); use AnyEvent::MP::Kernel; +use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID); use common::sense; use Carp (); use AE (); +use Guard (); use base "Exporter"; -our $VERSION = $AnyEvent::MP::Kernel::VERSION; +our $VERSION = $AnyEvent::MP::Config::VERSION; our @EXPORT = qw( NODE $NODE *SELF node_of after - resolve_node initialise_node - snd rcv mon mon_guard kil reg psub spawn + configure + snd rcv mon mon_guard kil psub peval spawn cal port + db_set db_del db_reg + db_mon db_family db_keys db_values ); our $SELF; @@ -143,149 +212,166 @@ =item $thisnode = NODE / $NODE -The C function returns, and the C<$NODE> variable contains the -node id of the local node. The value is initialised by a call to -C. +The C 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. =item $nodeid = node_of $port -Extracts and returns the noderef from a port ID or a node ID. - -=item initialise_node $profile_name +Extracts and returns the node ID from a port ID or a node ID. -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. +=item configure $profile, key => value... -This function initialises a node - it must be called exactly once (or -never) before calling other AnyEvent::MP functions. +=item configure key => value... -All arguments (optionally except for the first) are noderefs, which can be -either resolved or unresolved. +Before a node can talk to other nodes on the network (i.e. enter +"distributed mode") it has to configure itself - the minimum a node needs +to know is its own name, and optionally it should know the addresses of +some other nodes in the network to discover other nodes. -The first argument will be looked up in the configuration database first -(if it is C then the current nodename will be used instead) to find -the relevant configuration profile (see L). If none is found then -the default configuration is used. The configuration supplies additional -seed/master nodes and can override the actual noderef. +This function configures a node - it must be called exactly once (or +never) before calling other AnyEvent::MP functions. -There are two types of networked nodes, public nodes and slave nodes: +The key/value pairs are basically the same ones as documented for the +F command line utility (sans the set/del prefix), with these additions: =over 4 -=item public nodes - -For public nodes, C<$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). +=item norc => $boolean (default false) -After resolving, the node will bind itself on all endpoints. - -=item slave nodes - -When the C<$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 cannot talk to -each other (at least in this version of AnyEvent::MP). - -Slave nodes work by creating connections to all public nodes, using the -L service. - -=back +If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I +be consulted - all configuraiton options must be specified in the +C call. -After initialising itself, the node will connect to all additional -C<$seednodes> that are specified diretcly or via a profile. Seednodes are -optional and can be used to quickly bootstrap the node into an existing -network. +=item force => $boolean (default false) -All the seednodes will also be specially marked to automatically retry -connecting to them indefinitely, so make sure that seednodes are really -reliable and up (this might also change in the future). +IF true, then the values specified in the C 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. -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. +=item secure => $pass->($nodeid) - initialise_node; +In addition to specifying a boolean, you can specify a code reference that +is called for every remote execution attempt - the execution request is +granted iff the callback returns a true value. -Example: become a slave node to any of the the seednodes specified via -C. This form is often used for commandline clients. +See F for more info. - initialise_node "slave/"; - -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; +=back -Example: become a public node, only visible on localhost port 4044. +=over 4 - initialise_node "localhost:4044"; +=item step 1, gathering configuration from profiles -=item $cv = resolve_node $noderef +The function first looks up a profile in the aemp configuration (see the +L commandline utility). The profile name can be specified via the +named C parameter or can simply be the first parameter). If it is +missing, then the nodename (F) 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 utility), then the chain of +profiles chosen by the profile name (and any C attributes). + +That means that the values specified in the profile have highest priority +and the values specified directly via C 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) 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 commandline +utility uses C as nodename, which might expand to +C. + +=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 module, which will then use it to keep +connectivity with at least one node at any point in time. -Takes an unresolved node reference that may contain hostnames and -abbreviated IDs, resolves all of them and returns a resolved node -reference. +=back -In addition to C pairs allowed in resolved noderefs, the -following forms are supported: +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. -=over 4 + configure -=item the empty string +Example: become a semi-anonymous node. This form is often used for +commandline clients. -An empty-string component gets resolved as if the default port (4040) was -specified. + configure nodeid => "myscript/%n/%u"; -=item naked port numbers (e.g. C<1234>) +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). -These are resolved by prepending the local nodename and a colon, to be -further resolved. + # use the aemp commandline utility + # aemp profile seed binds '*:4040' -=item hostnames (e.g. C, C) + # then use it + configure profile => "seed"; -These are resolved by using AnyEvent::DNS to resolve them, optionally -looking up SRV records for the C port, if no port was -specified. + # or simply use aemp from the shell again: + # aemp run profile seed -=back + # or provide a nicer-to-remember nodeid + # aemp run profile seed nodeid "$(hostname)" =item $SELF Contains the current port id while executing C callbacks or C blocks. -=item SELF, %SELF, @SELF... +=item *SELF, SELF, %SELF, @SELF... Due to some quirks in how perl exports variables, it is impossible to -just export C<$SELF>, all the symbols called C are exported by this +just export C<$SELF>, all the symbols named C are exported by this module, but only C<$SELF> is currently used. =item snd $port, type => @data =item snd $port, @msg -Send the given message to the given port ID, which can identify either -a local or a remote port, and must be a port ID. +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 about anything, it is highly recommended to use a -string as first element (a port ID, or some word that indicates a request -type etc.). - -The message data effectively becomes read-only after a call to this -function: modifying any argument is not allowed and can cause many -problems. +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 +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 @@ -319,7 +405,7 @@ } sub port(;&) { - my $id = "$UNIQ." . $ID++; + my $id = $UNIQ . ++$ID; my $port = "$NODE#$id"; rcv $port, shift || \&_kilme; @@ -368,7 +454,7 @@ ; Example: temporarily register a rcv callback for a tag matching some port -(e.g. for a rpc reply) and unregister it after a message was received. +(e.g. for an rpc reply) and unregister it after a message was received. rcv $port, $otherport => sub { my @reply = @_; @@ -380,9 +466,9 @@ sub rcv($@) { my $port = shift; - my ($noderef, $portid) = split /#/, $port, 2; + my ($nodeid, $portid) = split /#/, $port, 2; - $NODE{$noderef} == $NODE{""} + $NODE{$nodeid} == $NODE{""} or Carp::croak "$port: rcv can only be called on local ports, caught"; while (@_) { @@ -391,7 +477,7 @@ "AnyEvent::MP::Port" eq ref $self or Carp::croak "$port: rcv can only be called on message matching ports, caught"; - $self->[2] = shift; + $self->[0] = shift; } else { my $cb = shift; $PORT{$portid} = sub { @@ -401,7 +487,7 @@ } } elsif (defined $_[0]) { my $self = $PORT_DATA{$portid} ||= do { - my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port"; + my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port"; $PORT{$portid} = sub { local $SELF = $port; @@ -433,12 +519,52 @@ $port } +=item peval $port, $coderef[, @args] + +Evaluates the given C<$codref> within the contetx of C<$port>, that is, +when the code throews an exception the C<$port> will be killed. + +Any remaining args will be passed to the callback. Any return values will +be returned to the caller. + +This is useful when you temporarily want to execute code in the context of +a port. + +Example: create a port and run some initialisation code in it's context. + + my $port = port { ... }; + + 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 + } +} + =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. +The effect is basically as if it returned C<< sub { peval $SELF, sub { +BLOCK }, @_ } >>. + This is useful when you register callbacks from C callbacks: rcv delayed_reply => sub { @@ -471,36 +597,25 @@ } } -=item $guard = mon $port, $cb->(@reason) +=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies -=item $guard = mon $port, $rcvport +=item $guard = mon $port, $rcvport # kill $rcvport when $port dies -=item $guard = mon $port +=item $guard = mon $port # kill $SELF when $port dies -=item $guard = mon $port, $rcvport, @msg +=item $guard = mon $port, $rcvport, @msg # send a message when $port dies Monitor the given port and do something when the port is killed or messages to it were lost, and optionally return a guard that can be used to stop monitoring again. -C effectively guarantees that, in the absence of hardware failures, -that after starting the monitor, either all messages sent to the port -will arrive, or the monitoring action will be invoked after possible -message loss has been detected. No messages will be lost "in between" -(after the first lost message no further messages will be received by the -port). After the monitoring action was invoked, further messages might get -delivered again. - -Note that monitoring-actions are one-shot: once released, they are removed -and will not trigger again. - In the first form (callback), the callback is simply called with any number of C<@reason> elements (no @reason means that the port was deleted "normally"). Note also that I<< the callback B never die >>, so use C if unsure. In the second form (another port given), the other port (C<$rcvport>) -will be C'ed with C<@reason>, iff a @reason was specified, i.e. on +will be C'ed with C<@reason>, if 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. @@ -510,13 +625,33 @@ In the last form (message), a message of the form C<@msg, @reason> will be C. +Monitoring-actions are one-shot: once messages are lost (and a monitoring +alert was raised), they are removed and will not trigger again. + 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 +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 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 $port, sub { warn "port died because of <@_>\n" }; @@ -532,9 +667,9 @@ =cut sub mon { - my ($noderef, $port) = split /#/, shift, 2; + my ($nodeid, $port) = split /#/, shift, 2; - my $node = $NODE{$noderef} || add_node $noderef; + my $node = $NODE{$nodeid} || add_node $nodeid; my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; @@ -553,7 +688,7 @@ $node->monitor ($port, $cb); defined wantarray - and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) } + and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) }) } =item $guard = mon_guard $port, $ref, $ref... @@ -564,10 +699,10 @@ Optionally returns a guard that will stop the monitoring. This function is useful when you create e.g. timers or other watchers and -want to free them when the port gets killed: +want to free them when the port gets killed (note the use of C): $port->rcv (start => sub { - my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { + my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub { undef $timer if 0.9 < rand; }); }); @@ -586,11 +721,12 @@ Kill the specified port with the given C<@reason>. -If no C<@reason> is specified, then the port is killed "normally" (linked -ports will not be kileld, or even notified). +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 form) to get killed. -Otherwise, linked ports get killed with the same reason (second form of -C, see below). +If a C<@reason> is specified, then linked ports (C +form) get killed with the same reason. Runtime errors while evaluating C callbacks or inside C blocks will be reported as reason C<< die => $@ >>. @@ -605,13 +741,13 @@ Creates a port on the node C<$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 return immediately, and it is -permissible to immediately start sending messages or monitor the port. +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. This function must be a fully-qualified function name -(e.g. C). To specify a function in the main -program, use C<::name>. +After the port has been created, the init function is called on the remote +node, in the same context as a C callback. This function must be a +fully-qualified function name (e.g. C). To +specify a function in the main program, use C<::name>. 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. @@ -619,11 +755,18 @@ exists or it runs out of package names. The init function is then called with the newly-created port as context -object (C<$SELF>) and the C<@initdata> values as arguments. - -A common idiom is to pass your own port, monitor the spawned port, and -in the init function, monitor the original port. This two-way monitoring -ensures that both ports get cleaned up when there is a problem. +object (C<$SELF>) and the C<@initdata> values as arguments. It I +call one of the C functions to set callbacks on C<$SELF>, otherwise +the port might not get created. + +A common idiom is to pass a local port, immediately monitor the spawned +port, and in the remote init function, immediately monitor the passed +local port. This two-way monitoring ensures that both ports get cleaned up +when there is a problem. + +C guarantees that the C<$initfunc> has no visible effects on the +caller before C returns (by delaying invocation when spawn is +called for the local node). Example: spawn a chat server port on C<$othernode>. @@ -648,6 +791,7 @@ my $port = shift; my $init = shift; + # rcv will create the actual port local $SELF = "$NODE#$port"; eval { &{ load_func $init } @@ -656,18 +800,19 @@ } sub spawn(@) { - my ($noderef, undef) = split /#/, shift, 2; + my ($nodeid, undef) = split /#/, shift, 2; - my $id = "$RUNIQ." . $ID++; + my $id = $RUNIQ . ++$ID; $_[0] =~ /::/ or Carp::croak "spawn init function must be a fully-qualified name, caught"; - snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_; + snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_; - "$noderef#$id" + "$nodeid#$id" } + =item after $timeout, @msg =item after $timeout, $callback @@ -675,7 +820,9 @@ Either sends the given message, or call the given callback, after the specified number of seconds. -This is simply a utility function that come sin handy at times. +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 @@ -690,6 +837,202 @@ }; } +#=item $cb2 = timeout $seconds, $cb[, @args] + +=item cal $port, @msg, $callback[, $timeout] + +A simple form of RPC - sends a message to the given C<$port> with the +given contents (C<@msg>), but adds a reply port to the message. + +The reply port is created temporarily just for the purpose of receiving +the reply, and will be Ced 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, +then the callback will be called without any arguments after the time-out +elapsed and the port is Ced. + +If no time-out is given (or it is C), 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 + +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 at all global nodes. Other nodes bind to one of +the global nodes for their needs. + +The database consists of a two-level hash - a hash contains a hash which +contains values. + +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. + +As the family namespace is global, it is recommended to prefix family names +with the name of the application or module using it. + +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 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 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] }; + }; + +In general, you can set or delete single subkeys, but query and monitor +whole families only. + +If you feel the need to monitor or query a single subkey, try giving it +it's own family. + +=over + +=item db_set $family => $subkey [=> $value] + +Sets (or replaces) a key to the database - if C<$value> is omitted, +C is used instead. + +=item db_del $family => $subkey + +Deletes a key from the database. + +=item $guard = db_reg $family => $subkey [=> $value] + +Sets the key on the database and returns a guard. When the guard is +destroyed, the key is deleted from the database. If C<$value> is missing, +then C is used. + +=item db_family $family => $cb->(\%familyhash) + +Queries the named database C<$family> and call the callback with the +family represented as a hash. You can keep and freely modify the hash. + +=item db_keys $family => $cb->(\@keys) + +Same as C, except it only queries the family I and passes +them as array reference to the callback. + +=item db_values $family => $cb->(\@values) + +Same as C, except it only queries the family I and passes them +as array reference to the callback. + +=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...) + +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 an arrayref with subkeys that have changed. + +Specifically, if one of the passed subkeys exists in the $familyhash, then +it is currently set to the value in the $familyhash. Otherwise, it has +been deleted. + +The family hash reference belongs to AnyEvent::MP and B by the callback. When in doubt, make a copy. + +The first call will be with the current contents of the family and all +keys, as if they were just added. + +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, $keys) = @_; + print "mygroup members: ", (join " ", keys %$family), "\n"; + }; + +Exmaple: wait until the family "My::Module::workers" is non-empty. + + my $guard; $guard = db_mon My::Module::workers => sub { + my ($family, $keys) = @_; + return unless %$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, $keys) = @_; + + for (@$keys) { + print "$_: ", + (exists $family->{$_} + ? $family->{$_} + : "(deleted)"), + "\n"; + } + }; + +=cut + =back =head1 AnyEvent::MP vs. Distributed Erlang @@ -699,23 +1042,21 @@ 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: =over 4 -=item * Node references contain the recipe on how to contact them. - -Erlang relies on special naming and DNS to work everywhere in the -same way. AEMP relies on each node knowing it's own address(es), with -convenience functionality. +=item * Node IDs are arbitrary strings in AEMP. -This means that AEMP requires a less tightly controlled environment at the -cost of longer node references and a slightly higher management overhead. +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". @@ -734,84 +1075,88 @@ =item * Erlang uses processes and a mailbox, AEMP does not queue. -Erlang uses processes that selectively receive messages, 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 dequeing them. +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. -(But see L for a more Erlang-like process model on top of AEMP). +You cna have a look at L 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 (and -so does not need a queue that can overflow). AEMP sends are immediate, -connection establishment is handled in the background. +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 makes 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 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 -alive. - -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. - -In AEMP, when port monitoring detects a port as dead, then that port will -eventually be killed - it cannot happen that a node detects a port as dead -and then later sends messages to it, finding it is still alive. +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 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. +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 never reuses port IDs, so old messages or old port IDs floating +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 - SSL/TLS - to protect connections and +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 -language-independent text-only protocols (good for debugging) and binary, -language-specific serialisers (e.g. Storable). +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 fucntionality to make the +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 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. +In Erlang, you can chose to receive I exit signals as messages or +I, 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, -as linking is (except linking is unreliable in Erlang). +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 the you, and you monitor -the remote port. Since both monitors are local to the node, they are much -more reliable. +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). This also saves round-trips and avoids sending messages to the wrong port (hard to do in Erlang). @@ -822,29 +1167,29 @@ =over 4 -=item Why strings for ports and noderefs, why not objects? +=item Why strings for port and node IDs, 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 +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. +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 a a miniport consists of a single closure stored in a global hash - it -can't become much cheaper. +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 real serialising format such as Storable? +=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. +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 gains: Just like function calls, objects simply do not travel +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. @@ -855,6 +1200,18 @@ =head1 SEE ALSO +L - a gentle introduction. + +L - more, lower-level, stuff. + +L - network maintenance and port groups, to find +your applications. + +L - establish data connections between nodes. + +L - simple service to display log messages from +all nodes. + L. =head1 AUTHOR