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1.1 |
=head1 NAME |
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1.89 |
AnyEvent::MP - erlang-style multi-processing/message-passing framework |
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1.1 |
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=head1 SYNOPSIS |
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use AnyEvent::MP; |
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1.75 |
$NODE # contains this node's node ID |
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NODE # returns this node's node ID |
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|
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$SELF # receiving/own port id in rcv callbacks |
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# initialise the node so it can send/receive messages |
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configure; |
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|
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# ports are message destinations |
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|
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# sending messages |
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snd $port, type => data...; |
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snd $port, @msg; |
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snd @msg_with_first_element_being_a_port; |
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|
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# creating/using ports, the simple way |
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my $simple_port = port { my @msg = @_ }; |
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|
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# creating/using ports, tagged message matching |
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my $port = port; |
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rcv $port, ping => sub { snd $_[0], "pong" }; |
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rcv $port, pong => sub { warn "pong received\n" }; |
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|
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# create a port on another node |
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my $port = spawn $node, $initfunc, @initdata; |
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# destroy a port again |
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kil $port; # "normal" kill |
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kil $port, my_error => "everything is broken"; # error kill |
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# monitoring |
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mon $localport, $cb->(@msg) # callback is invoked on death |
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mon $localport, $otherport # kill otherport on abnormal death |
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mon $localport, $otherport, @msg # send message on death |
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# temporarily execute code in port context |
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peval $port, sub { die "kill the port!" }; |
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# execute callbacks in $SELF port context |
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my $timer = AE::timer 1, 0, psub { |
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die "kill the port, delayed"; |
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}; |
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=head1 CURRENT STATUS |
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bin/aemp - stable. |
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AnyEvent::MP - stable API, should work. |
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1.77 |
AnyEvent::MP::Intro - explains most concepts. |
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AnyEvent::MP::Kernel - mostly stable API. |
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AnyEvent::MP::Global - stable API. |
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|
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1.1 |
=head1 DESCRIPTION |
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This module (-family) implements a simple message passing framework. |
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Despite its simplicity, you can securely message other processes running |
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1.67 |
on the same or other hosts, and you can supervise entities remotely. |
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|
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For an introduction to this module family, see the L<AnyEvent::MP::Intro> |
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manual page and the examples under F<eg/>. |
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|
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=head1 CONCEPTS |
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=over 4 |
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=item port |
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Not to be confused with a TCP port, a "port" is something you can send |
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messages to (with the C<snd> function). |
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1.29 |
|
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Ports allow you to register C<rcv> handlers that can match all or just |
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some messages. Messages send to ports will not be queued, regardless of |
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anything was listening for them or not. |
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|
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Ports are represented by (printable) strings called "port IDs". |
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=item port ID - C<nodeid#portname> |
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|
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A port ID is the concatenation of a node ID, a hash-mark (C<#>) |
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as separator, and a port name (a printable string of unspecified |
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format created by AnyEvent::MP). |
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|
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=item node |
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A node is a single process containing at least one port - the node port, |
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which enables nodes to manage each other remotely, and to create new |
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1.53 |
ports. |
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|
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Nodes are either public (have one or more listening ports) or private |
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(no listening ports). Private nodes cannot talk to other private nodes |
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currently, but all nodes can talk to public nodes. |
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Nodes is represented by (printable) strings called "node IDs". |
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|
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=item node ID - C<[A-Za-z0-9_\-.:]*> |
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|
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A node ID is a string that uniquely identifies the node within a |
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network. Depending on the configuration used, node IDs can look like a |
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hostname, a hostname and a port, or a random string. AnyEvent::MP itself |
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doesn't interpret node IDs in any way except to uniquely identify a node. |
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|
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=item binds - C<ip:port> |
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Nodes can only talk to each other by creating some kind of connection to |
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each other. To do this, nodes should listen on one or more local transport |
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endpoints - binds. |
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Currently, only standard C<ip:port> specifications can be used, which |
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specify TCP ports to listen on. So a bind is basically just a tcp socket |
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in listening mode thta accepts conenctions form other nodes. |
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|
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=item seed nodes |
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|
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When a node starts, it knows nothing about the network it is in - it |
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needs to connect to at least one other node that is already in the |
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network. These other nodes are called "seed nodes". |
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Seed nodes themselves are not special - they are seed nodes only because |
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some other node I<uses> them as such, but any node can be used as seed |
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node for other nodes, and eahc node cna use a different set of seed nodes. |
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|
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In addition to discovering the network, seed nodes are also used to |
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maintain the network - all nodes using the same seed node form are part of |
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the same network. If a network is split into multiple subnets because e.g. |
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the network link between the parts goes down, then using the same seed |
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nodes for all nodes ensures that eventually the subnets get merged again. |
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|
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Seed nodes are expected to be long-running, and at least one seed node |
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should always be available. They should also be relatively responsive - a |
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seed node that blocks for long periods will slow down everybody else. |
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|
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For small networks, it's best if every node uses the same set of seed |
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nodes. For large networks, it can be useful to specify "regional" seed |
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nodes for most nodes in an area, and use all seed nodes as seed nodes for |
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each other. What's important is that all seed nodes connections form a |
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complete graph, so that the network cannot split into separate subnets |
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forever. |
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Seed nodes are represented by seed IDs. |
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=item seed IDs - C<host:port> |
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1.83 |
|
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1.119 |
Seed IDs are transport endpoint(s) (usually a hostname/IP address and a |
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1.96 |
TCP port) of nodes that should be used as seed nodes. |
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1.29 |
|
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1.119 |
=item global nodes |
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|
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An AEMP network needs a discovery service - nodes need to know how to |
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connect to other nodes they only know by name. In addition, AEMP offers a |
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distributed "group database", which maps group names to a list of strings |
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- for example, to register worker ports. |
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A network needs at least one global node to work, and allows every node to |
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be a global node. |
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Any node that loads the L<AnyEvent::MP::Global> module becomes a global |
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node and tries to keep connections to all other nodes. So while it can |
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make sense to make every node "global" in small networks, it usually makes |
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sense to only make seed nodes into global nodes in large networks (nodes |
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keep connections to seed nodes and global nodes, so makign them the same |
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reduces overhead). |
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1.67 |
|
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1.2 |
=back |
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1.3 |
=head1 VARIABLES/FUNCTIONS |
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1.2 |
|
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=over 4 |
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1.1 |
=cut |
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package AnyEvent::MP; |
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1.121 |
use AnyEvent::MP::Config (); |
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1.44 |
use AnyEvent::MP::Kernel; |
183 |
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1.121 |
use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID); |
184 |
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1.2 |
|
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1.1 |
use common::sense; |
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1.2 |
use Carp (); |
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1.1 |
use AE (); |
190 |
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1.124 |
use Guard (); |
191 |
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1.1 |
|
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1.2 |
use base "Exporter"; |
193 |
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|
194 |
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1.121 |
our $VERSION = $AnyEvent::MP::Config::VERSION; |
195 |
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1.43 |
|
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1.8 |
our @EXPORT = qw( |
197 |
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1.59 |
NODE $NODE *SELF node_of after |
198 |
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1.72 |
configure |
199 |
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1.101 |
snd rcv mon mon_guard kil psub peval spawn cal |
200 |
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1.22 |
port |
201 |
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1.124 |
db_set db_del db_reg |
202 |
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1.8 |
); |
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1.2 |
|
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1.22 |
our $SELF; |
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206 |
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sub _self_die() { |
207 |
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my $msg = $@; |
208 |
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$msg =~ s/\n+$// unless ref $msg; |
209 |
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kil $SELF, die => $msg; |
210 |
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} |
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=item $thisnode = NODE / $NODE |
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The C<NODE> function returns, and the C<$NODE> variable contains, the node |
215 |
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1.64 |
ID of the node running in the current process. This value is initialised by |
216 |
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1.72 |
a call to C<configure>. |
217 |
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1.22 |
|
218 |
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1.63 |
=item $nodeid = node_of $port |
219 |
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1.22 |
|
220 |
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1.67 |
Extracts and returns the node ID from a port ID or a node ID. |
221 |
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1.34 |
|
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1.78 |
=item configure $profile, key => value... |
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1.72 |
=item configure key => value... |
225 |
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1.34 |
|
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1.64 |
Before a node can talk to other nodes on the network (i.e. enter |
227 |
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1.72 |
"distributed mode") it has to configure itself - the minimum a node needs |
228 |
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1.64 |
to know is its own name, and optionally it should know the addresses of |
229 |
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some other nodes in the network to discover other nodes. |
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1.34 |
|
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1.121 |
This function configures a node - it must be called exactly once (or |
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never) before calling other AnyEvent::MP functions. |
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|
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1.108 |
The key/value pairs are basically the same ones as documented for the |
235 |
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1.121 |
F<aemp> command line utility (sans the set/del prefix), with two additions: |
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|
237 |
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=over 4 |
238 |
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|
239 |
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=item norc => $boolean (default false) |
240 |
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241 |
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If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not> |
242 |
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be consulted - all configuraiton options must be specified in the |
243 |
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C<configure> call. |
244 |
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1.108 |
|
245 |
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1.121 |
=item force => $boolean (default false) |
246 |
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247 |
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IF true, then the values specified in the C<configure> will take |
248 |
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precedence over any values configured via the rc file. The default is for |
249 |
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the rc file to override any options specified in the program. |
250 |
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|
251 |
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=back |
252 |
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1.34 |
|
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1.72 |
=over 4 |
254 |
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255 |
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=item step 1, gathering configuration from profiles |
256 |
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257 |
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The function first looks up a profile in the aemp configuration (see the |
258 |
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L<aemp> commandline utility). The profile name can be specified via the |
259 |
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1.78 |
named C<profile> parameter or can simply be the first parameter). If it is |
260 |
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missing, then the nodename (F<uname -n>) will be used as profile name. |
261 |
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1.34 |
|
262 |
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1.72 |
The profile data is then gathered as follows: |
263 |
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1.69 |
|
264 |
elmex |
1.77 |
First, all remaining key => value pairs (all of which are conveniently |
265 |
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1.72 |
undocumented at the moment) will be interpreted as configuration |
266 |
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data. Then they will be overwritten by any values specified in the global |
267 |
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default configuration (see the F<aemp> utility), then the chain of |
268 |
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profiles chosen by the profile name (and any C<parent> attributes). |
269 |
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|
270 |
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That means that the values specified in the profile have highest priority |
271 |
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and the values specified directly via C<configure> have lowest priority, |
272 |
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and can only be used to specify defaults. |
273 |
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1.49 |
|
274 |
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1.64 |
If the profile specifies a node ID, then this will become the node ID of |
275 |
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1.122 |
this process. If not, then the profile name will be used as node ID, with |
276 |
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1.126 |
a unique randoms tring (C</%u>) appended. |
277 |
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1.122 |
|
278 |
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1.126 |
The node ID can contain some C<%> sequences that are expanded: C<%n> |
279 |
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is expanded to the local nodename, C<%u> is replaced by a random |
280 |
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strign to make the node unique. For example, the F<aemp> commandline |
281 |
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utility uses C<aemp/%n/%u> as nodename, which might expand to |
282 |
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C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>. |
283 |
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1.64 |
|
284 |
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1.72 |
=item step 2, bind listener sockets |
285 |
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|
286 |
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1.64 |
The next step is to look up the binds in the profile, followed by binding |
287 |
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aemp protocol listeners on all binds specified (it is possible and valid |
288 |
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to have no binds, meaning that the node cannot be contacted form the |
289 |
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outside. This means the node cannot talk to other nodes that also have no |
290 |
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binds, but it can still talk to all "normal" nodes). |
291 |
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|
292 |
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1.70 |
If the profile does not specify a binds list, then a default of C<*> is |
293 |
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1.72 |
used, meaning the node will bind on a dynamically-assigned port on every |
294 |
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local IP address it finds. |
295 |
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|
296 |
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=item step 3, connect to seed nodes |
297 |
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1.64 |
|
298 |
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1.119 |
As the last step, the seed ID list from the profile is passed to the |
299 |
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1.64 |
L<AnyEvent::MP::Global> module, which will then use it to keep |
300 |
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1.72 |
connectivity with at least one node at any point in time. |
301 |
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1.64 |
|
302 |
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1.72 |
=back |
303 |
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|
304 |
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1.87 |
Example: become a distributed node using the local node name as profile. |
305 |
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1.72 |
This should be the most common form of invocation for "daemon"-type nodes. |
306 |
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1.34 |
|
307 |
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1.72 |
configure |
308 |
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1.34 |
|
309 |
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1.126 |
Example: become a semi-anonymous node. This form is often used for |
310 |
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commandline clients. |
311 |
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1.34 |
|
312 |
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1.126 |
configure nodeid => "myscript/%n/%u"; |
313 |
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1.72 |
|
314 |
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1.120 |
Example: configure a node using a profile called seed, which is suitable |
315 |
root |
1.72 |
for a seed node as it binds on all local addresses on a fixed port (4040, |
316 |
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customary for aemp). |
317 |
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|
318 |
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# use the aemp commandline utility |
319 |
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1.122 |
# aemp profile seed binds '*:4040' |
320 |
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1.72 |
|
321 |
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# then use it |
322 |
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configure profile => "seed"; |
323 |
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1.34 |
|
324 |
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1.72 |
# or simply use aemp from the shell again: |
325 |
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# aemp run profile seed |
326 |
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1.34 |
|
327 |
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1.72 |
# or provide a nicer-to-remember nodeid |
328 |
|
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# aemp run profile seed nodeid "$(hostname)" |
329 |
root |
1.34 |
|
330 |
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1.22 |
=item $SELF |
331 |
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|
332 |
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Contains the current port id while executing C<rcv> callbacks or C<psub> |
333 |
|
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blocks. |
334 |
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1.3 |
|
335 |
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1.67 |
=item *SELF, SELF, %SELF, @SELF... |
336 |
root |
1.22 |
|
337 |
|
|
Due to some quirks in how perl exports variables, it is impossible to |
338 |
root |
1.67 |
just export C<$SELF>, all the symbols named C<SELF> are exported by this |
339 |
root |
1.22 |
module, but only C<$SELF> is currently used. |
340 |
root |
1.3 |
|
341 |
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1.33 |
=item snd $port, type => @data |
342 |
root |
1.3 |
|
343 |
root |
1.33 |
=item snd $port, @msg |
344 |
root |
1.3 |
|
345 |
root |
1.67 |
Send the given message to the given port, which can identify either a |
346 |
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|
local or a remote port, and must be a port ID. |
347 |
root |
1.8 |
|
348 |
root |
1.67 |
While the message can be almost anything, it is highly recommended to |
349 |
|
|
use a string as first element (a port ID, or some word that indicates a |
350 |
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request type etc.) and to consist if only simple perl values (scalars, |
351 |
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arrays, hashes) - if you think you need to pass an object, think again. |
352 |
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|
353 |
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The message data logically becomes read-only after a call to this |
354 |
|
|
function: modifying any argument (or values referenced by them) is |
355 |
|
|
forbidden, as there can be considerable time between the call to C<snd> |
356 |
|
|
and the time the message is actually being serialised - in fact, it might |
357 |
|
|
never be copied as within the same process it is simply handed to the |
358 |
|
|
receiving port. |
359 |
root |
1.3 |
|
360 |
|
|
The type of data you can transfer depends on the transport protocol: when |
361 |
|
|
JSON is used, then only strings, numbers and arrays and hashes consisting |
362 |
|
|
of those are allowed (no objects). When Storable is used, then anything |
363 |
|
|
that Storable can serialise and deserialise is allowed, and for the local |
364 |
root |
1.67 |
node, anything can be passed. Best rely only on the common denominator of |
365 |
|
|
these. |
366 |
root |
1.3 |
|
367 |
root |
1.22 |
=item $local_port = port |
368 |
root |
1.2 |
|
369 |
root |
1.50 |
Create a new local port object and returns its port ID. Initially it has |
370 |
|
|
no callbacks set and will throw an error when it receives messages. |
371 |
root |
1.10 |
|
372 |
root |
1.50 |
=item $local_port = port { my @msg = @_ } |
373 |
root |
1.15 |
|
374 |
root |
1.50 |
Creates a new local port, and returns its ID. Semantically the same as |
375 |
|
|
creating a port and calling C<rcv $port, $callback> on it. |
376 |
root |
1.15 |
|
377 |
root |
1.50 |
The block will be called for every message received on the port, with the |
378 |
|
|
global variable C<$SELF> set to the port ID. Runtime errors will cause the |
379 |
|
|
port to be C<kil>ed. The message will be passed as-is, no extra argument |
380 |
|
|
(i.e. no port ID) will be passed to the callback. |
381 |
root |
1.15 |
|
382 |
root |
1.50 |
If you want to stop/destroy the port, simply C<kil> it: |
383 |
root |
1.15 |
|
384 |
root |
1.50 |
my $port = port { |
385 |
|
|
my @msg = @_; |
386 |
|
|
... |
387 |
|
|
kil $SELF; |
388 |
root |
1.15 |
}; |
389 |
root |
1.10 |
|
390 |
|
|
=cut |
391 |
|
|
|
392 |
root |
1.33 |
sub rcv($@); |
393 |
|
|
|
394 |
root |
1.50 |
sub _kilme { |
395 |
|
|
die "received message on port without callback"; |
396 |
|
|
} |
397 |
|
|
|
398 |
root |
1.22 |
sub port(;&) { |
399 |
root |
1.123 |
my $id = $UNIQ . ++$ID; |
400 |
root |
1.22 |
my $port = "$NODE#$id"; |
401 |
|
|
|
402 |
root |
1.50 |
rcv $port, shift || \&_kilme; |
403 |
root |
1.10 |
|
404 |
root |
1.22 |
$port |
405 |
root |
1.10 |
} |
406 |
|
|
|
407 |
root |
1.50 |
=item rcv $local_port, $callback->(@msg) |
408 |
root |
1.31 |
|
409 |
root |
1.50 |
Replaces the default callback on the specified port. There is no way to |
410 |
|
|
remove the default callback: use C<sub { }> to disable it, or better |
411 |
|
|
C<kil> the port when it is no longer needed. |
412 |
root |
1.3 |
|
413 |
root |
1.33 |
The global C<$SELF> (exported by this module) contains C<$port> while |
414 |
root |
1.50 |
executing the callback. Runtime errors during callback execution will |
415 |
|
|
result in the port being C<kil>ed. |
416 |
root |
1.22 |
|
417 |
root |
1.50 |
The default callback received all messages not matched by a more specific |
418 |
|
|
C<tag> match. |
419 |
root |
1.22 |
|
420 |
root |
1.50 |
=item rcv $local_port, tag => $callback->(@msg_without_tag), ... |
421 |
root |
1.3 |
|
422 |
root |
1.54 |
Register (or replace) callbacks to be called on messages starting with the |
423 |
|
|
given tag on the given port (and return the port), or unregister it (when |
424 |
|
|
C<$callback> is C<$undef> or missing). There can only be one callback |
425 |
|
|
registered for each tag. |
426 |
root |
1.3 |
|
427 |
root |
1.50 |
The original message will be passed to the callback, after the first |
428 |
|
|
element (the tag) has been removed. The callback will use the same |
429 |
|
|
environment as the default callback (see above). |
430 |
root |
1.3 |
|
431 |
root |
1.36 |
Example: create a port and bind receivers on it in one go. |
432 |
|
|
|
433 |
|
|
my $port = rcv port, |
434 |
root |
1.50 |
msg1 => sub { ... }, |
435 |
|
|
msg2 => sub { ... }, |
436 |
root |
1.36 |
; |
437 |
|
|
|
438 |
|
|
Example: create a port, bind receivers and send it in a message elsewhere |
439 |
|
|
in one go: |
440 |
|
|
|
441 |
|
|
snd $otherport, reply => |
442 |
|
|
rcv port, |
443 |
root |
1.50 |
msg1 => sub { ... }, |
444 |
root |
1.36 |
... |
445 |
|
|
; |
446 |
|
|
|
447 |
root |
1.54 |
Example: temporarily register a rcv callback for a tag matching some port |
448 |
root |
1.102 |
(e.g. for an rpc reply) and unregister it after a message was received. |
449 |
root |
1.54 |
|
450 |
|
|
rcv $port, $otherport => sub { |
451 |
|
|
my @reply = @_; |
452 |
|
|
|
453 |
|
|
rcv $SELF, $otherport; |
454 |
|
|
}; |
455 |
|
|
|
456 |
root |
1.3 |
=cut |
457 |
|
|
|
458 |
|
|
sub rcv($@) { |
459 |
root |
1.33 |
my $port = shift; |
460 |
root |
1.75 |
my ($nodeid, $portid) = split /#/, $port, 2; |
461 |
root |
1.3 |
|
462 |
root |
1.75 |
$NODE{$nodeid} == $NODE{""} |
463 |
root |
1.33 |
or Carp::croak "$port: rcv can only be called on local ports, caught"; |
464 |
root |
1.22 |
|
465 |
root |
1.50 |
while (@_) { |
466 |
|
|
if (ref $_[0]) { |
467 |
|
|
if (my $self = $PORT_DATA{$portid}) { |
468 |
|
|
"AnyEvent::MP::Port" eq ref $self |
469 |
|
|
or Carp::croak "$port: rcv can only be called on message matching ports, caught"; |
470 |
root |
1.33 |
|
471 |
root |
1.103 |
$self->[0] = shift; |
472 |
root |
1.50 |
} else { |
473 |
|
|
my $cb = shift; |
474 |
|
|
$PORT{$portid} = sub { |
475 |
|
|
local $SELF = $port; |
476 |
|
|
eval { &$cb }; _self_die if $@; |
477 |
|
|
}; |
478 |
|
|
} |
479 |
|
|
} elsif (defined $_[0]) { |
480 |
|
|
my $self = $PORT_DATA{$portid} ||= do { |
481 |
root |
1.103 |
my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port"; |
482 |
root |
1.50 |
|
483 |
|
|
$PORT{$portid} = sub { |
484 |
|
|
local $SELF = $port; |
485 |
|
|
|
486 |
|
|
if (my $cb = $self->[1]{$_[0]}) { |
487 |
|
|
shift; |
488 |
|
|
eval { &$cb }; _self_die if $@; |
489 |
|
|
} else { |
490 |
|
|
&{ $self->[0] }; |
491 |
root |
1.33 |
} |
492 |
|
|
}; |
493 |
root |
1.50 |
|
494 |
|
|
$self |
495 |
root |
1.33 |
}; |
496 |
|
|
|
497 |
root |
1.50 |
"AnyEvent::MP::Port" eq ref $self |
498 |
|
|
or Carp::croak "$port: rcv can only be called on message matching ports, caught"; |
499 |
root |
1.22 |
|
500 |
root |
1.50 |
my ($tag, $cb) = splice @_, 0, 2; |
501 |
root |
1.33 |
|
502 |
root |
1.50 |
if (defined $cb) { |
503 |
|
|
$self->[1]{$tag} = $cb; |
504 |
root |
1.33 |
} else { |
505 |
root |
1.50 |
delete $self->[1]{$tag}; |
506 |
root |
1.33 |
} |
507 |
root |
1.22 |
} |
508 |
root |
1.3 |
} |
509 |
root |
1.31 |
|
510 |
root |
1.33 |
$port |
511 |
root |
1.2 |
} |
512 |
|
|
|
513 |
root |
1.101 |
=item peval $port, $coderef[, @args] |
514 |
|
|
|
515 |
|
|
Evaluates the given C<$codref> within the contetx of C<$port>, that is, |
516 |
|
|
when the code throews an exception the C<$port> will be killed. |
517 |
|
|
|
518 |
|
|
Any remaining args will be passed to the callback. Any return values will |
519 |
|
|
be returned to the caller. |
520 |
|
|
|
521 |
|
|
This is useful when you temporarily want to execute code in the context of |
522 |
|
|
a port. |
523 |
|
|
|
524 |
|
|
Example: create a port and run some initialisation code in it's context. |
525 |
|
|
|
526 |
|
|
my $port = port { ... }; |
527 |
|
|
|
528 |
|
|
peval $port, sub { |
529 |
|
|
init |
530 |
|
|
or die "unable to init"; |
531 |
|
|
}; |
532 |
|
|
|
533 |
|
|
=cut |
534 |
|
|
|
535 |
|
|
sub peval($$) { |
536 |
|
|
local $SELF = shift; |
537 |
|
|
my $cb = shift; |
538 |
|
|
|
539 |
|
|
if (wantarray) { |
540 |
|
|
my @res = eval { &$cb }; |
541 |
|
|
_self_die if $@; |
542 |
|
|
@res |
543 |
|
|
} else { |
544 |
|
|
my $res = eval { &$cb }; |
545 |
|
|
_self_die if $@; |
546 |
|
|
$res |
547 |
|
|
} |
548 |
|
|
} |
549 |
|
|
|
550 |
root |
1.22 |
=item $closure = psub { BLOCK } |
551 |
root |
1.2 |
|
552 |
root |
1.22 |
Remembers C<$SELF> and creates a closure out of the BLOCK. When the |
553 |
|
|
closure is executed, sets up the environment in the same way as in C<rcv> |
554 |
|
|
callbacks, i.e. runtime errors will cause the port to get C<kil>ed. |
555 |
|
|
|
556 |
root |
1.101 |
The effect is basically as if it returned C<< sub { peval $SELF, sub { |
557 |
root |
1.114 |
BLOCK }, @_ } >>. |
558 |
root |
1.101 |
|
559 |
root |
1.22 |
This is useful when you register callbacks from C<rcv> callbacks: |
560 |
|
|
|
561 |
|
|
rcv delayed_reply => sub { |
562 |
|
|
my ($delay, @reply) = @_; |
563 |
|
|
my $timer = AE::timer $delay, 0, psub { |
564 |
|
|
snd @reply, $SELF; |
565 |
|
|
}; |
566 |
|
|
}; |
567 |
root |
1.3 |
|
568 |
root |
1.8 |
=cut |
569 |
root |
1.3 |
|
570 |
root |
1.22 |
sub psub(&) { |
571 |
|
|
my $cb = shift; |
572 |
root |
1.3 |
|
573 |
root |
1.22 |
my $port = $SELF |
574 |
|
|
or Carp::croak "psub can only be called from within rcv or psub callbacks, not"; |
575 |
root |
1.1 |
|
576 |
root |
1.22 |
sub { |
577 |
|
|
local $SELF = $port; |
578 |
root |
1.2 |
|
579 |
root |
1.22 |
if (wantarray) { |
580 |
|
|
my @res = eval { &$cb }; |
581 |
|
|
_self_die if $@; |
582 |
|
|
@res |
583 |
|
|
} else { |
584 |
|
|
my $res = eval { &$cb }; |
585 |
|
|
_self_die if $@; |
586 |
|
|
$res |
587 |
|
|
} |
588 |
|
|
} |
589 |
root |
1.2 |
} |
590 |
|
|
|
591 |
root |
1.67 |
=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies |
592 |
root |
1.32 |
|
593 |
root |
1.67 |
=item $guard = mon $port, $rcvport # kill $rcvport when $port dies |
594 |
root |
1.36 |
|
595 |
root |
1.67 |
=item $guard = mon $port # kill $SELF when $port dies |
596 |
root |
1.32 |
|
597 |
root |
1.67 |
=item $guard = mon $port, $rcvport, @msg # send a message when $port dies |
598 |
root |
1.32 |
|
599 |
root |
1.42 |
Monitor the given port and do something when the port is killed or |
600 |
|
|
messages to it were lost, and optionally return a guard that can be used |
601 |
|
|
to stop monitoring again. |
602 |
|
|
|
603 |
root |
1.36 |
In the first form (callback), the callback is simply called with any |
604 |
|
|
number of C<@reason> elements (no @reason means that the port was deleted |
605 |
root |
1.32 |
"normally"). Note also that I<< the callback B<must> never die >>, so use |
606 |
|
|
C<eval> if unsure. |
607 |
|
|
|
608 |
root |
1.43 |
In the second form (another port given), the other port (C<$rcvport>) |
609 |
elmex |
1.77 |
will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on |
610 |
root |
1.36 |
"normal" kils nothing happens, while under all other conditions, the other |
611 |
|
|
port is killed with the same reason. |
612 |
root |
1.32 |
|
613 |
root |
1.36 |
The third form (kill self) is the same as the second form, except that |
614 |
|
|
C<$rvport> defaults to C<$SELF>. |
615 |
|
|
|
616 |
|
|
In the last form (message), a message of the form C<@msg, @reason> will be |
617 |
|
|
C<snd>. |
618 |
root |
1.32 |
|
619 |
root |
1.79 |
Monitoring-actions are one-shot: once messages are lost (and a monitoring |
620 |
|
|
alert was raised), they are removed and will not trigger again. |
621 |
|
|
|
622 |
root |
1.37 |
As a rule of thumb, monitoring requests should always monitor a port from |
623 |
|
|
a local port (or callback). The reason is that kill messages might get |
624 |
|
|
lost, just like any other message. Another less obvious reason is that |
625 |
elmex |
1.77 |
even monitoring requests can get lost (for example, when the connection |
626 |
root |
1.37 |
to the other node goes down permanently). When monitoring a port locally |
627 |
|
|
these problems do not exist. |
628 |
|
|
|
629 |
root |
1.79 |
C<mon> effectively guarantees that, in the absence of hardware failures, |
630 |
|
|
after starting the monitor, either all messages sent to the port will |
631 |
|
|
arrive, or the monitoring action will be invoked after possible message |
632 |
|
|
loss has been detected. No messages will be lost "in between" (after |
633 |
|
|
the first lost message no further messages will be received by the |
634 |
|
|
port). After the monitoring action was invoked, further messages might get |
635 |
|
|
delivered again. |
636 |
|
|
|
637 |
|
|
Inter-host-connection timeouts and monitoring depend on the transport |
638 |
|
|
used. The only transport currently implemented is TCP, and AnyEvent::MP |
639 |
|
|
relies on TCP to detect node-downs (this can take 10-15 minutes on a |
640 |
elmex |
1.96 |
non-idle connection, and usually around two hours for idle connections). |
641 |
root |
1.79 |
|
642 |
|
|
This means that monitoring is good for program errors and cleaning up |
643 |
|
|
stuff eventually, but they are no replacement for a timeout when you need |
644 |
|
|
to ensure some maximum latency. |
645 |
|
|
|
646 |
root |
1.32 |
Example: call a given callback when C<$port> is killed. |
647 |
|
|
|
648 |
|
|
mon $port, sub { warn "port died because of <@_>\n" }; |
649 |
|
|
|
650 |
|
|
Example: kill ourselves when C<$port> is killed abnormally. |
651 |
|
|
|
652 |
root |
1.36 |
mon $port; |
653 |
root |
1.32 |
|
654 |
root |
1.36 |
Example: send us a restart message when another C<$port> is killed. |
655 |
root |
1.32 |
|
656 |
|
|
mon $port, $self => "restart"; |
657 |
|
|
|
658 |
|
|
=cut |
659 |
|
|
|
660 |
|
|
sub mon { |
661 |
root |
1.75 |
my ($nodeid, $port) = split /#/, shift, 2; |
662 |
root |
1.32 |
|
663 |
root |
1.75 |
my $node = $NODE{$nodeid} || add_node $nodeid; |
664 |
root |
1.32 |
|
665 |
root |
1.41 |
my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; |
666 |
root |
1.32 |
|
667 |
|
|
unless (ref $cb) { |
668 |
|
|
if (@_) { |
669 |
|
|
# send a kill info message |
670 |
root |
1.41 |
my (@msg) = ($cb, @_); |
671 |
root |
1.32 |
$cb = sub { snd @msg, @_ }; |
672 |
|
|
} else { |
673 |
|
|
# simply kill other port |
674 |
|
|
my $port = $cb; |
675 |
|
|
$cb = sub { kil $port, @_ if @_ }; |
676 |
|
|
} |
677 |
|
|
} |
678 |
|
|
|
679 |
|
|
$node->monitor ($port, $cb); |
680 |
|
|
|
681 |
|
|
defined wantarray |
682 |
root |
1.124 |
and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) }) |
683 |
root |
1.32 |
} |
684 |
|
|
|
685 |
|
|
=item $guard = mon_guard $port, $ref, $ref... |
686 |
|
|
|
687 |
|
|
Monitors the given C<$port> and keeps the passed references. When the port |
688 |
|
|
is killed, the references will be freed. |
689 |
|
|
|
690 |
|
|
Optionally returns a guard that will stop the monitoring. |
691 |
|
|
|
692 |
|
|
This function is useful when you create e.g. timers or other watchers and |
693 |
root |
1.67 |
want to free them when the port gets killed (note the use of C<psub>): |
694 |
root |
1.32 |
|
695 |
|
|
$port->rcv (start => sub { |
696 |
root |
1.67 |
my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub { |
697 |
root |
1.32 |
undef $timer if 0.9 < rand; |
698 |
|
|
}); |
699 |
|
|
}); |
700 |
|
|
|
701 |
|
|
=cut |
702 |
|
|
|
703 |
|
|
sub mon_guard { |
704 |
|
|
my ($port, @refs) = @_; |
705 |
|
|
|
706 |
root |
1.36 |
#TODO: mon-less form? |
707 |
|
|
|
708 |
root |
1.32 |
mon $port, sub { 0 && @refs } |
709 |
|
|
} |
710 |
|
|
|
711 |
root |
1.33 |
=item kil $port[, @reason] |
712 |
root |
1.32 |
|
713 |
|
|
Kill the specified port with the given C<@reason>. |
714 |
|
|
|
715 |
root |
1.107 |
If no C<@reason> is specified, then the port is killed "normally" - |
716 |
|
|
monitor callback will be invoked, but the kil will not cause linked ports |
717 |
|
|
(C<mon $mport, $lport> form) to get killed. |
718 |
root |
1.32 |
|
719 |
root |
1.107 |
If a C<@reason> is specified, then linked ports (C<mon $mport, $lport> |
720 |
|
|
form) get killed with the same reason. |
721 |
root |
1.32 |
|
722 |
|
|
Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks |
723 |
|
|
will be reported as reason C<< die => $@ >>. |
724 |
|
|
|
725 |
|
|
Transport/communication errors are reported as C<< transport_error => |
726 |
|
|
$message >>. |
727 |
|
|
|
728 |
root |
1.38 |
=cut |
729 |
|
|
|
730 |
|
|
=item $port = spawn $node, $initfunc[, @initdata] |
731 |
|
|
|
732 |
|
|
Creates a port on the node C<$node> (which can also be a port ID, in which |
733 |
|
|
case it's the node where that port resides). |
734 |
|
|
|
735 |
root |
1.67 |
The port ID of the newly created port is returned immediately, and it is |
736 |
|
|
possible to immediately start sending messages or to monitor the port. |
737 |
root |
1.38 |
|
738 |
root |
1.67 |
After the port has been created, the init function is called on the remote |
739 |
|
|
node, in the same context as a C<rcv> callback. This function must be a |
740 |
|
|
fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To |
741 |
|
|
specify a function in the main program, use C<::name>. |
742 |
root |
1.38 |
|
743 |
|
|
If the function doesn't exist, then the node tries to C<require> |
744 |
|
|
the package, then the package above the package and so on (e.g. |
745 |
|
|
C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function |
746 |
|
|
exists or it runs out of package names. |
747 |
|
|
|
748 |
|
|
The init function is then called with the newly-created port as context |
749 |
root |
1.82 |
object (C<$SELF>) and the C<@initdata> values as arguments. It I<must> |
750 |
|
|
call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise |
751 |
|
|
the port might not get created. |
752 |
root |
1.38 |
|
753 |
root |
1.67 |
A common idiom is to pass a local port, immediately monitor the spawned |
754 |
|
|
port, and in the remote init function, immediately monitor the passed |
755 |
|
|
local port. This two-way monitoring ensures that both ports get cleaned up |
756 |
|
|
when there is a problem. |
757 |
root |
1.38 |
|
758 |
root |
1.80 |
C<spawn> guarantees that the C<$initfunc> has no visible effects on the |
759 |
|
|
caller before C<spawn> returns (by delaying invocation when spawn is |
760 |
|
|
called for the local node). |
761 |
|
|
|
762 |
root |
1.38 |
Example: spawn a chat server port on C<$othernode>. |
763 |
|
|
|
764 |
|
|
# this node, executed from within a port context: |
765 |
|
|
my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; |
766 |
|
|
mon $server; |
767 |
|
|
|
768 |
|
|
# init function on C<$othernode> |
769 |
|
|
sub connect { |
770 |
|
|
my ($srcport) = @_; |
771 |
|
|
|
772 |
|
|
mon $srcport; |
773 |
|
|
|
774 |
|
|
rcv $SELF, sub { |
775 |
|
|
... |
776 |
|
|
}; |
777 |
|
|
} |
778 |
|
|
|
779 |
|
|
=cut |
780 |
|
|
|
781 |
|
|
sub _spawn { |
782 |
|
|
my $port = shift; |
783 |
|
|
my $init = shift; |
784 |
|
|
|
785 |
root |
1.82 |
# rcv will create the actual port |
786 |
root |
1.38 |
local $SELF = "$NODE#$port"; |
787 |
|
|
eval { |
788 |
|
|
&{ load_func $init } |
789 |
|
|
}; |
790 |
|
|
_self_die if $@; |
791 |
|
|
} |
792 |
|
|
|
793 |
|
|
sub spawn(@) { |
794 |
root |
1.75 |
my ($nodeid, undef) = split /#/, shift, 2; |
795 |
root |
1.38 |
|
796 |
root |
1.123 |
my $id = $RUNIQ . ++$ID; |
797 |
root |
1.38 |
|
798 |
root |
1.39 |
$_[0] =~ /::/ |
799 |
|
|
or Carp::croak "spawn init function must be a fully-qualified name, caught"; |
800 |
|
|
|
801 |
root |
1.75 |
snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_; |
802 |
root |
1.38 |
|
803 |
root |
1.75 |
"$nodeid#$id" |
804 |
root |
1.38 |
} |
805 |
|
|
|
806 |
root |
1.121 |
|
807 |
root |
1.59 |
=item after $timeout, @msg |
808 |
|
|
|
809 |
|
|
=item after $timeout, $callback |
810 |
|
|
|
811 |
|
|
Either sends the given message, or call the given callback, after the |
812 |
|
|
specified number of seconds. |
813 |
|
|
|
814 |
root |
1.67 |
This is simply a utility function that comes in handy at times - the |
815 |
|
|
AnyEvent::MP author is not convinced of the wisdom of having it, though, |
816 |
|
|
so it may go away in the future. |
817 |
root |
1.59 |
|
818 |
|
|
=cut |
819 |
|
|
|
820 |
|
|
sub after($@) { |
821 |
|
|
my ($timeout, @action) = @_; |
822 |
|
|
|
823 |
|
|
my $t; $t = AE::timer $timeout, 0, sub { |
824 |
|
|
undef $t; |
825 |
|
|
ref $action[0] |
826 |
|
|
? $action[0]() |
827 |
|
|
: snd @action; |
828 |
|
|
}; |
829 |
|
|
} |
830 |
|
|
|
831 |
root |
1.87 |
=item cal $port, @msg, $callback[, $timeout] |
832 |
|
|
|
833 |
|
|
A simple form of RPC - sends a message to the given C<$port> with the |
834 |
|
|
given contents (C<@msg>), but adds a reply port to the message. |
835 |
|
|
|
836 |
|
|
The reply port is created temporarily just for the purpose of receiving |
837 |
|
|
the reply, and will be C<kil>ed when no longer needed. |
838 |
|
|
|
839 |
|
|
A reply message sent to the port is passed to the C<$callback> as-is. |
840 |
|
|
|
841 |
|
|
If an optional time-out (in seconds) is given and it is not C<undef>, |
842 |
|
|
then the callback will be called without any arguments after the time-out |
843 |
|
|
elapsed and the port is C<kil>ed. |
844 |
|
|
|
845 |
root |
1.98 |
If no time-out is given (or it is C<undef>), then the local port will |
846 |
|
|
monitor the remote port instead, so it eventually gets cleaned-up. |
847 |
root |
1.87 |
|
848 |
|
|
Currently this function returns the temporary port, but this "feature" |
849 |
|
|
might go in future versions unless you can make a convincing case that |
850 |
|
|
this is indeed useful for something. |
851 |
|
|
|
852 |
|
|
=cut |
853 |
|
|
|
854 |
|
|
sub cal(@) { |
855 |
|
|
my $timeout = ref $_[-1] ? undef : pop; |
856 |
|
|
my $cb = pop; |
857 |
|
|
|
858 |
|
|
my $port = port { |
859 |
|
|
undef $timeout; |
860 |
|
|
kil $SELF; |
861 |
|
|
&$cb; |
862 |
|
|
}; |
863 |
|
|
|
864 |
|
|
if (defined $timeout) { |
865 |
|
|
$timeout = AE::timer $timeout, 0, sub { |
866 |
|
|
undef $timeout; |
867 |
|
|
kil $port; |
868 |
|
|
$cb->(); |
869 |
|
|
}; |
870 |
|
|
} else { |
871 |
|
|
mon $_[0], sub { |
872 |
|
|
kil $port; |
873 |
|
|
$cb->(); |
874 |
|
|
}; |
875 |
|
|
} |
876 |
|
|
|
877 |
|
|
push @_, $port; |
878 |
|
|
&snd; |
879 |
|
|
|
880 |
|
|
$port |
881 |
|
|
} |
882 |
|
|
|
883 |
root |
1.8 |
=back |
884 |
|
|
|
885 |
root |
1.124 |
=head1 DISTRIBUTED DATABASE |
886 |
|
|
|
887 |
|
|
AnyEvent::MP comes with a simple distributed database. The database will |
888 |
|
|
be mirrored asynchronously at all global nodes. Other nodes bind to one of |
889 |
|
|
the global nodes for their needs. |
890 |
|
|
|
891 |
|
|
The database consists of a two-level hash - a hash contains a hash which |
892 |
|
|
contains values. |
893 |
|
|
|
894 |
|
|
The top level hash key is called "family", and the second-level hash key |
895 |
root |
1.126 |
is called "subkey" or simply "key". |
896 |
root |
1.124 |
|
897 |
root |
1.125 |
The family must be alphanumeric, i.e. start with a letter and consist |
898 |
|
|
of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>, |
899 |
|
|
pretty much like Perl module names. |
900 |
root |
1.124 |
|
901 |
root |
1.125 |
As the family namespace is global, it is recommended to prefix family names |
902 |
root |
1.124 |
with the name of the application or module using it. |
903 |
|
|
|
904 |
root |
1.126 |
The subkeys must be non-empty strings, with no further restrictions. |
905 |
root |
1.125 |
|
906 |
root |
1.124 |
The values should preferably be strings, but other perl scalars should |
907 |
root |
1.125 |
work as well (such as undef, arrays and hashes). |
908 |
root |
1.124 |
|
909 |
root |
1.126 |
Every database entry is owned by one node - adding the same family/subkey |
910 |
root |
1.124 |
combination on multiple nodes will not cause discomfort for AnyEvent::MP, |
911 |
|
|
but the result might be nondeterministic, i.e. the key might have |
912 |
|
|
different values on different nodes. |
913 |
|
|
|
914 |
root |
1.126 |
Different subkeys in the same family can be owned by different nodes |
915 |
|
|
without problems, and in fact, this is the common method to create worker |
916 |
|
|
pools. For example, a worker port for image scaling might do this: |
917 |
root |
1.124 |
|
918 |
root |
1.126 |
db_set my_image_scalers => $port; |
919 |
root |
1.124 |
|
920 |
root |
1.126 |
And clients looking for an image scaler will want to get the |
921 |
|
|
C<my_image_scalers> keys: |
922 |
|
|
|
923 |
|
|
db_keys "my_image_scalers" => 60 => sub { |
924 |
|
|
#d##TODO# |
925 |
|
|
|
926 |
|
|
=over |
927 |
|
|
|
928 |
|
|
=item db_set $family => $subkey [=> $value] |
929 |
|
|
|
930 |
|
|
Sets (or replaces) a key to the database - if C<$value> is omitted, |
931 |
|
|
C<undef> is used instead. |
932 |
|
|
|
933 |
|
|
=item db_del $family => $subkey |
934 |
root |
1.124 |
|
935 |
|
|
Deletes a key from the database. |
936 |
|
|
|
937 |
root |
1.126 |
=item $guard = db_reg $family => $subkey [=> $value] |
938 |
root |
1.124 |
|
939 |
|
|
Sets the key on the database and returns a guard. When the guard is |
940 |
|
|
destroyed, the key is deleted from the database. If C<$value> is missing, |
941 |
|
|
then C<undef> is used. |
942 |
|
|
|
943 |
|
|
=cut |
944 |
|
|
|
945 |
|
|
=back |
946 |
|
|
|
947 |
root |
1.26 |
=head1 AnyEvent::MP vs. Distributed Erlang |
948 |
|
|
|
949 |
root |
1.35 |
AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node |
950 |
|
|
== aemp node, Erlang process == aemp port), so many of the documents and |
951 |
|
|
programming techniques employed by Erlang apply to AnyEvent::MP. Here is a |
952 |
root |
1.27 |
sample: |
953 |
|
|
|
954 |
root |
1.95 |
http://www.erlang.se/doc/programming_rules.shtml |
955 |
|
|
http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4 |
956 |
|
|
http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6 |
957 |
|
|
http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5 |
958 |
root |
1.27 |
|
959 |
|
|
Despite the similarities, there are also some important differences: |
960 |
root |
1.26 |
|
961 |
|
|
=over 4 |
962 |
|
|
|
963 |
root |
1.65 |
=item * Node IDs are arbitrary strings in AEMP. |
964 |
root |
1.26 |
|
965 |
root |
1.65 |
Erlang relies on special naming and DNS to work everywhere in the same |
966 |
|
|
way. AEMP relies on each node somehow knowing its own address(es) (e.g. by |
967 |
root |
1.99 |
configuration or DNS), and possibly the addresses of some seed nodes, but |
968 |
|
|
will otherwise discover other nodes (and their IDs) itself. |
969 |
root |
1.27 |
|
970 |
root |
1.54 |
=item * Erlang has a "remote ports are like local ports" philosophy, AEMP |
971 |
root |
1.51 |
uses "local ports are like remote ports". |
972 |
|
|
|
973 |
|
|
The failure modes for local ports are quite different (runtime errors |
974 |
|
|
only) then for remote ports - when a local port dies, you I<know> it dies, |
975 |
|
|
when a connection to another node dies, you know nothing about the other |
976 |
|
|
port. |
977 |
|
|
|
978 |
|
|
Erlang pretends remote ports are as reliable as local ports, even when |
979 |
|
|
they are not. |
980 |
|
|
|
981 |
|
|
AEMP encourages a "treat remote ports differently" philosophy, with local |
982 |
|
|
ports being the special case/exception, where transport errors cannot |
983 |
|
|
occur. |
984 |
|
|
|
985 |
root |
1.26 |
=item * Erlang uses processes and a mailbox, AEMP does not queue. |
986 |
|
|
|
987 |
root |
1.119 |
Erlang uses processes that selectively receive messages out of order, and |
988 |
|
|
therefore needs a queue. AEMP is event based, queuing messages would serve |
989 |
|
|
no useful purpose. For the same reason the pattern-matching abilities |
990 |
|
|
of AnyEvent::MP are more limited, as there is little need to be able to |
991 |
elmex |
1.77 |
filter messages without dequeuing them. |
992 |
root |
1.26 |
|
993 |
root |
1.119 |
This is not a philosophical difference, but simply stems from AnyEvent::MP |
994 |
|
|
being event-based, while Erlang is process-based. |
995 |
|
|
|
996 |
|
|
You cna have a look at L<Coro::MP> for a more Erlang-like process model on |
997 |
|
|
top of AEMP and Coro threads. |
998 |
root |
1.26 |
|
999 |
|
|
=item * Erlang sends are synchronous, AEMP sends are asynchronous. |
1000 |
|
|
|
1001 |
root |
1.119 |
Sending messages in Erlang is synchronous and blocks the process until |
1002 |
|
|
a conenction has been established and the message sent (and so does not |
1003 |
|
|
need a queue that can overflow). AEMP sends return immediately, connection |
1004 |
|
|
establishment is handled in the background. |
1005 |
root |
1.26 |
|
1006 |
root |
1.51 |
=item * Erlang suffers from silent message loss, AEMP does not. |
1007 |
root |
1.26 |
|
1008 |
root |
1.99 |
Erlang implements few guarantees on messages delivery - messages can get |
1009 |
|
|
lost without any of the processes realising it (i.e. you send messages a, |
1010 |
|
|
b, and c, and the other side only receives messages a and c). |
1011 |
root |
1.26 |
|
1012 |
root |
1.117 |
AEMP guarantees (modulo hardware errors) correct ordering, and the |
1013 |
|
|
guarantee that after one message is lost, all following ones sent to the |
1014 |
|
|
same port are lost as well, until monitoring raises an error, so there are |
1015 |
|
|
no silent "holes" in the message sequence. |
1016 |
root |
1.26 |
|
1017 |
root |
1.119 |
If you want your software to be very reliable, you have to cope with |
1018 |
|
|
corrupted and even out-of-order messages in both Erlang and AEMP. AEMP |
1019 |
|
|
simply tries to work better in common error cases, such as when a network |
1020 |
|
|
link goes down. |
1021 |
|
|
|
1022 |
root |
1.26 |
=item * Erlang can send messages to the wrong port, AEMP does not. |
1023 |
|
|
|
1024 |
root |
1.119 |
In Erlang it is quite likely that a node that restarts reuses an Erlang |
1025 |
|
|
process ID known to other nodes for a completely different process, |
1026 |
|
|
causing messages destined for that process to end up in an unrelated |
1027 |
|
|
process. |
1028 |
root |
1.26 |
|
1029 |
root |
1.119 |
AEMP does not reuse port IDs, so old messages or old port IDs floating |
1030 |
root |
1.26 |
around in the network will not be sent to an unrelated port. |
1031 |
|
|
|
1032 |
|
|
=item * Erlang uses unprotected connections, AEMP uses secure |
1033 |
|
|
authentication and can use TLS. |
1034 |
|
|
|
1035 |
root |
1.66 |
AEMP can use a proven protocol - TLS - to protect connections and |
1036 |
root |
1.26 |
securely authenticate nodes. |
1037 |
|
|
|
1038 |
root |
1.28 |
=item * The AEMP protocol is optimised for both text-based and binary |
1039 |
|
|
communications. |
1040 |
|
|
|
1041 |
root |
1.66 |
The AEMP protocol, unlike the Erlang protocol, supports both programming |
1042 |
root |
1.119 |
language independent text-only protocols (good for debugging), and binary, |
1043 |
root |
1.67 |
language-specific serialisers (e.g. Storable). By default, unless TLS is |
1044 |
|
|
used, the protocol is actually completely text-based. |
1045 |
root |
1.28 |
|
1046 |
|
|
It has also been carefully designed to be implementable in other languages |
1047 |
root |
1.66 |
with a minimum of work while gracefully degrading functionality to make the |
1048 |
root |
1.28 |
protocol simple. |
1049 |
|
|
|
1050 |
root |
1.35 |
=item * AEMP has more flexible monitoring options than Erlang. |
1051 |
|
|
|
1052 |
root |
1.119 |
In Erlang, you can chose to receive I<all> exit signals as messages or |
1053 |
|
|
I<none>, there is no in-between, so monitoring single Erlang processes is |
1054 |
|
|
difficult to implement. |
1055 |
|
|
|
1056 |
|
|
Monitoring in AEMP is more flexible than in Erlang, as one can choose |
1057 |
|
|
between automatic kill, exit message or callback on a per-port basis. |
1058 |
root |
1.35 |
|
1059 |
root |
1.37 |
=item * Erlang tries to hide remote/local connections, AEMP does not. |
1060 |
root |
1.35 |
|
1061 |
root |
1.67 |
Monitoring in Erlang is not an indicator of process death/crashes, in the |
1062 |
|
|
same way as linking is (except linking is unreliable in Erlang). |
1063 |
root |
1.37 |
|
1064 |
|
|
In AEMP, you don't "look up" registered port names or send to named ports |
1065 |
|
|
that might or might not be persistent. Instead, you normally spawn a port |
1066 |
root |
1.67 |
on the remote node. The init function monitors you, and you monitor the |
1067 |
|
|
remote port. Since both monitors are local to the node, they are much more |
1068 |
|
|
reliable (no need for C<spawn_link>). |
1069 |
root |
1.37 |
|
1070 |
|
|
This also saves round-trips and avoids sending messages to the wrong port |
1071 |
|
|
(hard to do in Erlang). |
1072 |
root |
1.35 |
|
1073 |
root |
1.26 |
=back |
1074 |
|
|
|
1075 |
root |
1.46 |
=head1 RATIONALE |
1076 |
|
|
|
1077 |
|
|
=over 4 |
1078 |
|
|
|
1079 |
root |
1.67 |
=item Why strings for port and node IDs, why not objects? |
1080 |
root |
1.46 |
|
1081 |
|
|
We considered "objects", but found that the actual number of methods |
1082 |
root |
1.67 |
that can be called are quite low. Since port and node IDs travel over |
1083 |
root |
1.46 |
the network frequently, the serialising/deserialising would add lots of |
1084 |
root |
1.67 |
overhead, as well as having to keep a proxy object everywhere. |
1085 |
root |
1.46 |
|
1086 |
|
|
Strings can easily be printed, easily serialised etc. and need no special |
1087 |
|
|
procedures to be "valid". |
1088 |
|
|
|
1089 |
root |
1.110 |
And as a result, a port with just a default receiver consists of a single |
1090 |
root |
1.117 |
code reference stored in a global hash - it can't become much cheaper. |
1091 |
root |
1.47 |
|
1092 |
root |
1.67 |
=item Why favour JSON, why not a real serialising format such as Storable? |
1093 |
root |
1.46 |
|
1094 |
|
|
In fact, any AnyEvent::MP node will happily accept Storable as framing |
1095 |
|
|
format, but currently there is no way to make a node use Storable by |
1096 |
root |
1.67 |
default (although all nodes will accept it). |
1097 |
root |
1.46 |
|
1098 |
|
|
The default framing protocol is JSON because a) JSON::XS is many times |
1099 |
|
|
faster for small messages and b) most importantly, after years of |
1100 |
|
|
experience we found that object serialisation is causing more problems |
1101 |
root |
1.67 |
than it solves: Just like function calls, objects simply do not travel |
1102 |
root |
1.46 |
easily over the network, mostly because they will always be a copy, so you |
1103 |
|
|
always have to re-think your design. |
1104 |
|
|
|
1105 |
|
|
Keeping your messages simple, concentrating on data structures rather than |
1106 |
|
|
objects, will keep your messages clean, tidy and efficient. |
1107 |
|
|
|
1108 |
|
|
=back |
1109 |
|
|
|
1110 |
root |
1.1 |
=head1 SEE ALSO |
1111 |
|
|
|
1112 |
root |
1.68 |
L<AnyEvent::MP::Intro> - a gentle introduction. |
1113 |
|
|
|
1114 |
|
|
L<AnyEvent::MP::Kernel> - more, lower-level, stuff. |
1115 |
|
|
|
1116 |
root |
1.113 |
L<AnyEvent::MP::Global> - network maintenance and port groups, to find |
1117 |
root |
1.68 |
your applications. |
1118 |
|
|
|
1119 |
root |
1.105 |
L<AnyEvent::MP::DataConn> - establish data connections between nodes. |
1120 |
|
|
|
1121 |
root |
1.81 |
L<AnyEvent::MP::LogCatcher> - simple service to display log messages from |
1122 |
|
|
all nodes. |
1123 |
|
|
|
1124 |
root |
1.1 |
L<AnyEvent>. |
1125 |
|
|
|
1126 |
|
|
=head1 AUTHOR |
1127 |
|
|
|
1128 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
1129 |
|
|
http://home.schmorp.de/ |
1130 |
|
|
|
1131 |
|
|
=cut |
1132 |
|
|
|
1133 |
|
|
1 |
1134 |
|
|
|