1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | AnyEvent::MP - multi-processing/message-passing framework |
3 | AnyEvent::MP - erlang-style multi-processing/message-passing framework |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use AnyEvent::MP; |
7 | use AnyEvent::MP; |
8 | |
8 | |
9 | $NODE # contains this node's noderef |
9 | $NODE # contains this node's node ID |
10 | NODE # returns this node's noderef |
10 | NODE # returns this node's node ID |
11 | NODE $port # returns the noderef of the port |
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12 | |
11 | |
13 | $SELF # receiving/own port id in rcv callbacks |
12 | $SELF # receiving/own port id in rcv callbacks |
14 | |
13 | |
15 | # initialise the node so it can send/receive messages |
14 | # initialise the node so it can send/receive messages |
16 | initialise_node; # -OR- |
15 | configure; |
17 | initialise_node "localhost:4040"; # -OR- |
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18 | initialise_node "slave/", "localhost:4040" |
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19 | |
16 | |
20 | # ports are message endpoints |
17 | # ports are message destinations |
21 | |
18 | |
22 | # sending messages |
19 | # sending messages |
23 | snd $port, type => data...; |
20 | snd $port, type => data...; |
24 | snd $port, @msg; |
21 | snd $port, @msg; |
25 | snd @msg_with_first_element_being_a_port; |
22 | snd @msg_with_first_element_being_a_port; |
26 | |
23 | |
27 | # creating/using ports, the simple way |
24 | # creating/using ports, the simple way |
28 | my $somple_port = port { my @msg = @_; 0 }; |
25 | my $simple_port = port { my @msg = @_ }; |
29 | |
26 | |
30 | # creating/using ports, type matching |
27 | # creating/using ports, tagged message matching |
31 | my $port = port; |
28 | my $port = port; |
32 | rcv $port, ping => sub { snd $_[0], "pong"; 0 }; |
29 | rcv $port, ping => sub { snd $_[0], "pong" }; |
33 | rcv $port, pong => sub { warn "pong received\n"; 0 }; |
30 | rcv $port, pong => sub { warn "pong received\n" }; |
34 | |
31 | |
35 | # create a port on another node |
32 | # create a port on another node |
36 | my $port = spawn $node, $initfunc, @initdata; |
33 | my $port = spawn $node, $initfunc, @initdata; |
37 | |
34 | |
38 | # monitoring |
35 | # monitoring |
… | |
… | |
40 | mon $port, $otherport # kill otherport on abnormal death |
37 | mon $port, $otherport # kill otherport on abnormal death |
41 | mon $port, $otherport, @msg # send message on death |
38 | mon $port, $otherport, @msg # send message on death |
42 | |
39 | |
43 | =head1 CURRENT STATUS |
40 | =head1 CURRENT STATUS |
44 | |
41 | |
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42 | bin/aemp - stable. |
45 | AnyEvent::MP - stable API, should work |
43 | AnyEvent::MP - stable API, should work. |
46 | AnyEvent::MP::Intro - outdated |
44 | AnyEvent::MP::Intro - explains most concepts. |
47 | AnyEvent::MP::Kernel - WIP |
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48 | AnyEvent::MP::Transport - mostly stable |
45 | AnyEvent::MP::Kernel - mostly stable API. |
49 | |
46 | AnyEvent::MP::Global - stable API. |
50 | stay tuned. |
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51 | |
47 | |
52 | =head1 DESCRIPTION |
48 | =head1 DESCRIPTION |
53 | |
49 | |
54 | This module (-family) implements a simple message passing framework. |
50 | This module (-family) implements a simple message passing framework. |
55 | |
51 | |
56 | Despite its simplicity, you can securely message other processes running |
52 | Despite its simplicity, you can securely message other processes running |
57 | on the same or other hosts. |
53 | on the same or other hosts, and you can supervise entities remotely. |
58 | |
54 | |
59 | For an introduction to this module family, see the L<AnyEvent::MP::Intro> |
55 | For an introduction to this module family, see the L<AnyEvent::MP::Intro> |
60 | manual page. |
56 | manual page and the examples under F<eg/>. |
61 | |
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62 | At the moment, this module family is severly broken and underdocumented, |
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63 | so do not use. This was uploaded mainly to reserve the CPAN namespace - |
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64 | stay tuned! |
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65 | |
57 | |
66 | =head1 CONCEPTS |
58 | =head1 CONCEPTS |
67 | |
59 | |
68 | =over 4 |
60 | =over 4 |
69 | |
61 | |
70 | =item port |
62 | =item port |
71 | |
63 | |
72 | A port is something you can send messages to (with the C<snd> function). |
64 | Not to be confused with a TCP port, a "port" is something you can send |
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65 | messages to (with the C<snd> function). |
73 | |
66 | |
74 | Some ports allow you to register C<rcv> handlers that can match specific |
67 | Ports allow you to register C<rcv> handlers that can match all or just |
75 | messages. All C<rcv> handlers will receive messages they match, messages |
68 | some messages. Messages send to ports will not be queued, regardless of |
76 | will not be queued. |
69 | anything was listening for them or not. |
77 | |
70 | |
78 | =item port id - C<noderef#portname> |
71 | =item port ID - C<nodeid#portname> |
79 | |
72 | |
80 | A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as |
73 | A port ID is the concatenation of a node ID, a hash-mark (C<#>) as |
81 | separator, and a port name (a printable string of unspecified format). An |
74 | separator, and a port name (a printable string of unspecified format). |
82 | exception is the the node port, whose ID is identical to its node |
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83 | reference. |
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84 | |
75 | |
85 | =item node |
76 | =item node |
86 | |
77 | |
87 | A node is a single process containing at least one port - the node |
78 | A node is a single process containing at least one port - the node port, |
88 | port. You can send messages to node ports to find existing ports or to |
79 | which enables nodes to manage each other remotely, and to create new |
89 | create new ports, among other things. |
80 | ports. |
90 | |
81 | |
91 | Nodes are either private (single-process only), slaves (connected to a |
82 | Nodes are either public (have one or more listening ports) or private |
92 | master node only) or public nodes (connectable from unrelated nodes). |
83 | (no listening ports). Private nodes cannot talk to other private nodes |
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84 | currently. |
93 | |
85 | |
94 | =item noderef - C<host:port,host:port...>, C<id@noderef>, C<id> |
86 | =item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*> |
95 | |
87 | |
96 | A node reference is a string that either simply identifies the node (for |
88 | A node ID is a string that uniquely identifies the node within a |
97 | private and slave nodes), or contains a recipe on how to reach a given |
89 | network. Depending on the configuration used, node IDs can look like a |
98 | node (for public nodes). |
90 | hostname, a hostname and a port, or a random string. AnyEvent::MP itself |
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91 | doesn't interpret node IDs in any way. |
99 | |
92 | |
100 | This recipe is simply a comma-separated list of C<address:port> pairs (for |
93 | =item binds - C<ip:port> |
101 | TCP/IP, other protocols might look different). |
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102 | |
94 | |
103 | Node references come in two flavours: resolved (containing only numerical |
95 | Nodes can only talk to each other by creating some kind of connection to |
104 | addresses) or unresolved (where hostnames are used instead of addresses). |
96 | each other. To do this, nodes should listen on one or more local transport |
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97 | endpoints - binds. Currently, only standard C<ip:port> specifications can |
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98 | be used, which specify TCP ports to listen on. |
105 | |
99 | |
106 | Before using an unresolved node reference in a message you first have to |
100 | =item seed nodes |
107 | resolve it. |
101 | |
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102 | When a node starts, it knows nothing about the network. To teach the node |
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103 | about the network it first has to contact some other node within the |
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104 | network. This node is called a seed. |
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105 | |
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106 | Apart from the fact that other nodes know them as seed nodes and they have |
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107 | to have fixed listening addresses, seed nodes are perfectly normal nodes - |
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108 | any node can function as a seed node for others. |
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109 | |
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110 | In addition to discovering the network, seed nodes are also used to |
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111 | maintain the network and to connect nodes that otherwise would have |
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112 | trouble connecting. They form the backbone of an AnyEvent::MP network. |
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113 | |
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114 | Seed nodes are expected to be long-running, and at least one seed node |
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115 | should always be available. They should also be relatively responsive - a |
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116 | seed node that blocks for long periods will slow down everybody else. |
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117 | |
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118 | =item seeds - C<host:port> |
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119 | |
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120 | Seeds are transport endpoint(s) (usually a hostname/IP address and a |
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121 | TCP port) of nodes thta should be used as seed nodes. |
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122 | |
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123 | The nodes listening on those endpoints are expected to be long-running, |
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124 | and at least one of those should always be available. When nodes run out |
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125 | of connections (e.g. due to a network error), they try to re-establish |
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126 | connections to some seednodes again to join the network. |
108 | |
127 | |
109 | =back |
128 | =back |
110 | |
129 | |
111 | =head1 VARIABLES/FUNCTIONS |
130 | =head1 VARIABLES/FUNCTIONS |
112 | |
131 | |
… | |
… | |
127 | use base "Exporter"; |
146 | use base "Exporter"; |
128 | |
147 | |
129 | our $VERSION = $AnyEvent::MP::Kernel::VERSION; |
148 | our $VERSION = $AnyEvent::MP::Kernel::VERSION; |
130 | |
149 | |
131 | our @EXPORT = qw( |
150 | our @EXPORT = qw( |
132 | NODE $NODE *SELF node_of _any_ |
151 | NODE $NODE *SELF node_of after |
133 | resolve_node initialise_node |
152 | configure |
134 | snd rcv mon kil reg psub spawn |
153 | snd rcv mon mon_guard kil reg psub spawn cal |
135 | port |
154 | port |
136 | ); |
155 | ); |
137 | |
156 | |
138 | our $SELF; |
157 | our $SELF; |
139 | |
158 | |
… | |
… | |
143 | kil $SELF, die => $msg; |
162 | kil $SELF, die => $msg; |
144 | } |
163 | } |
145 | |
164 | |
146 | =item $thisnode = NODE / $NODE |
165 | =item $thisnode = NODE / $NODE |
147 | |
166 | |
148 | The C<NODE> function returns, and the C<$NODE> variable contains |
167 | The C<NODE> function returns, and the C<$NODE> variable contains, the node |
149 | the noderef of the local node. The value is initialised by a call |
168 | ID of the node running in the current process. This value is initialised by |
150 | to C<become_public> or C<become_slave>, after which all local port |
169 | a call to C<configure>. |
151 | identifiers become invalid. |
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152 | |
170 | |
153 | =item $noderef = node_of $port |
171 | =item $nodeid = node_of $port |
154 | |
172 | |
155 | Extracts and returns the noderef from a portid or a noderef. |
173 | Extracts and returns the node ID from a port ID or a node ID. |
156 | |
174 | |
157 | =item initialise_node $noderef, $seednode, $seednode... |
175 | =item configure $profile, key => value... |
158 | |
176 | |
159 | =item initialise_node "slave/", $master, $master... |
177 | =item configure key => value... |
160 | |
178 | |
161 | Before a node can talk to other nodes on the network it has to initialise |
179 | Before a node can talk to other nodes on the network (i.e. enter |
162 | itself - the minimum a node needs to know is it's own name, and optionally |
180 | "distributed mode") it has to configure itself - the minimum a node needs |
163 | it should know the noderefs of some other nodes in the network. |
181 | to know is its own name, and optionally it should know the addresses of |
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182 | some other nodes in the network to discover other nodes. |
164 | |
183 | |
165 | This function initialises a node - it must be called exactly once (or |
184 | This function configures a node - it must be called exactly once (or |
166 | never) before calling other AnyEvent::MP functions. |
185 | never) before calling other AnyEvent::MP functions. |
167 | |
186 | |
168 | All arguments (optionally except for the first) are noderefs, which can be |
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169 | either resolved or unresolved. |
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170 | |
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171 | The first argument will be looked up in the configuration database first |
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172 | (if it is C<undef> then the current nodename will be used instead) to find |
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173 | the relevant configuration profile (see L<aemp>). If none is found then |
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174 | the default configuration is used. The configuration supplies additional |
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175 | seed/master nodes and can override the actual noderef. |
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176 | |
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177 | There are two types of networked nodes, public nodes and slave nodes: |
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178 | |
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179 | =over 4 |
187 | =over 4 |
180 | |
188 | |
181 | =item public nodes |
189 | =item step 1, gathering configuration from profiles |
182 | |
190 | |
183 | For public nodes, C<$noderef> (supplied either directly to |
191 | The function first looks up a profile in the aemp configuration (see the |
184 | C<initialise_node> or indirectly via a profile or the nodename) must be a |
192 | L<aemp> commandline utility). The profile name can be specified via the |
185 | noderef (possibly unresolved, in which case it will be resolved). |
193 | named C<profile> parameter or can simply be the first parameter). If it is |
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194 | missing, then the nodename (F<uname -n>) will be used as profile name. |
186 | |
195 | |
187 | After resolving, the node will bind itself on all endpoints and try to |
196 | The profile data is then gathered as follows: |
188 | connect to all additional C<$seednodes> that are specified. Seednodes are |
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189 | optional and can be used to quickly bootstrap the node into an existing |
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190 | network. |
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191 | |
197 | |
192 | =item slave nodes |
198 | First, all remaining key => value pairs (all of which are conveniently |
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199 | undocumented at the moment) will be interpreted as configuration |
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200 | data. Then they will be overwritten by any values specified in the global |
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201 | default configuration (see the F<aemp> utility), then the chain of |
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202 | profiles chosen by the profile name (and any C<parent> attributes). |
193 | |
203 | |
194 | When the C<$noderef> (either as given or overriden by the config file) |
204 | That means that the values specified in the profile have highest priority |
195 | is the special string C<slave/>, then the node will become a slave |
205 | and the values specified directly via C<configure> have lowest priority, |
196 | node. Slave nodes cannot be contacted from outside and will route most of |
206 | and can only be used to specify defaults. |
197 | their traffic to the master node that they attach to. |
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198 | |
207 | |
199 | At least one additional noderef is required (either by specifying it |
208 | If the profile specifies a node ID, then this will become the node ID of |
200 | directly or because it is part of the configuration profile): The node |
209 | this process. If not, then the profile name will be used as node ID. The |
201 | will try to connect to all of them and will become a slave attached to the |
210 | special node ID of C<anon/> will be replaced by a random node ID. |
202 | first node it can successfully connect to. |
211 | |
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212 | =item step 2, bind listener sockets |
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213 | |
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214 | The next step is to look up the binds in the profile, followed by binding |
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215 | aemp protocol listeners on all binds specified (it is possible and valid |
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216 | to have no binds, meaning that the node cannot be contacted form the |
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217 | outside. This means the node cannot talk to other nodes that also have no |
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218 | binds, but it can still talk to all "normal" nodes). |
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219 | |
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220 | If the profile does not specify a binds list, then a default of C<*> is |
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221 | used, meaning the node will bind on a dynamically-assigned port on every |
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222 | local IP address it finds. |
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223 | |
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224 | =item step 3, connect to seed nodes |
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225 | |
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226 | As the last step, the seeds list from the profile is passed to the |
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227 | L<AnyEvent::MP::Global> module, which will then use it to keep |
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228 | connectivity with at least one node at any point in time. |
203 | |
229 | |
204 | =back |
230 | =back |
205 | |
231 | |
206 | This function will block until all nodes have been resolved and, for slave |
232 | Example: become a distributed node using the local node name as profile. |
207 | nodes, until it has successfully established a connection to a master |
233 | This should be the most common form of invocation for "daemon"-type nodes. |
208 | server. |
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209 | |
234 | |
210 | Example: become a public node listening on the guessed noderef, or the one |
235 | configure |
211 | specified via C<aemp> for the current node. This should be the most common |
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212 | form of invocation for "daemon"-type nodes. |
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213 | |
236 | |
214 | initialise_node; |
237 | Example: become an anonymous node. This form is often used for commandline |
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238 | clients. |
215 | |
239 | |
216 | Example: become a slave node to any of the the seednodes specified via |
240 | configure nodeid => "anon/"; |
217 | C<aemp>. This form is often used for commandline clients. |
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218 | |
241 | |
219 | initialise_node "slave/"; |
242 | Example: configure a node using a profile called seed, which si suitable |
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243 | for a seed node as it binds on all local addresses on a fixed port (4040, |
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244 | customary for aemp). |
220 | |
245 | |
221 | Example: become a slave node to any of the specified master servers. This |
246 | # use the aemp commandline utility |
222 | form is also often used for commandline clients. |
247 | # aemp profile seed nodeid anon/ binds '*:4040' |
223 | |
248 | |
224 | initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net"; |
249 | # then use it |
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250 | configure profile => "seed"; |
225 | |
251 | |
226 | Example: become a public node, and try to contact some well-known master |
252 | # or simply use aemp from the shell again: |
227 | servers to become part of the network. |
253 | # aemp run profile seed |
228 | |
254 | |
229 | initialise_node undef, "master1", "master2"; |
255 | # or provide a nicer-to-remember nodeid |
230 | |
256 | # aemp run profile seed nodeid "$(hostname)" |
231 | Example: become a public node listening on port C<4041>. |
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232 | |
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233 | initialise_node 4041; |
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234 | |
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235 | Example: become a public node, only visible on localhost port 4044. |
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236 | |
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237 | initialise_node "localhost:4044"; |
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238 | |
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239 | =item $cv = resolve_node $noderef |
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240 | |
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241 | Takes an unresolved node reference that may contain hostnames and |
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242 | abbreviated IDs, resolves all of them and returns a resolved node |
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243 | reference. |
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244 | |
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245 | In addition to C<address:port> pairs allowed in resolved noderefs, the |
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246 | following forms are supported: |
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247 | |
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248 | =over 4 |
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249 | |
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250 | =item the empty string |
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251 | |
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252 | An empty-string component gets resolved as if the default port (4040) was |
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253 | specified. |
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254 | |
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255 | =item naked port numbers (e.g. C<1234>) |
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256 | |
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257 | These are resolved by prepending the local nodename and a colon, to be |
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258 | further resolved. |
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259 | |
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260 | =item hostnames (e.g. C<localhost:1234>, C<localhost>) |
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261 | |
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262 | These are resolved by using AnyEvent::DNS to resolve them, optionally |
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263 | looking up SRV records for the C<aemp=4040> port, if no port was |
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264 | specified. |
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265 | |
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266 | =back |
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267 | |
257 | |
268 | =item $SELF |
258 | =item $SELF |
269 | |
259 | |
270 | Contains the current port id while executing C<rcv> callbacks or C<psub> |
260 | Contains the current port id while executing C<rcv> callbacks or C<psub> |
271 | blocks. |
261 | blocks. |
272 | |
262 | |
273 | =item SELF, %SELF, @SELF... |
263 | =item *SELF, SELF, %SELF, @SELF... |
274 | |
264 | |
275 | Due to some quirks in how perl exports variables, it is impossible to |
265 | Due to some quirks in how perl exports variables, it is impossible to |
276 | just export C<$SELF>, all the symbols called C<SELF> are exported by this |
266 | just export C<$SELF>, all the symbols named C<SELF> are exported by this |
277 | module, but only C<$SELF> is currently used. |
267 | module, but only C<$SELF> is currently used. |
278 | |
268 | |
279 | =item snd $port, type => @data |
269 | =item snd $port, type => @data |
280 | |
270 | |
281 | =item snd $port, @msg |
271 | =item snd $port, @msg |
282 | |
272 | |
283 | Send the given message to the given port ID, which can identify either |
273 | Send the given message to the given port, which can identify either a |
284 | a local or a remote port, and can be either a string or soemthignt hat |
274 | local or a remote port, and must be a port ID. |
285 | stringifies a sa port ID (such as a port object :). |
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286 | |
275 | |
287 | While the message can be about anything, it is highly recommended to use a |
276 | While the message can be almost anything, it is highly recommended to |
288 | string as first element (a portid, or some word that indicates a request |
277 | use a string as first element (a port ID, or some word that indicates a |
289 | type etc.). |
278 | request type etc.) and to consist if only simple perl values (scalars, |
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279 | arrays, hashes) - if you think you need to pass an object, think again. |
290 | |
280 | |
291 | The message data effectively becomes read-only after a call to this |
281 | The message data logically becomes read-only after a call to this |
292 | function: modifying any argument is not allowed and can cause many |
282 | function: modifying any argument (or values referenced by them) is |
293 | problems. |
283 | forbidden, as there can be considerable time between the call to C<snd> |
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284 | and the time the message is actually being serialised - in fact, it might |
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285 | never be copied as within the same process it is simply handed to the |
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286 | receiving port. |
294 | |
287 | |
295 | The type of data you can transfer depends on the transport protocol: when |
288 | The type of data you can transfer depends on the transport protocol: when |
296 | JSON is used, then only strings, numbers and arrays and hashes consisting |
289 | JSON is used, then only strings, numbers and arrays and hashes consisting |
297 | of those are allowed (no objects). When Storable is used, then anything |
290 | of those are allowed (no objects). When Storable is used, then anything |
298 | that Storable can serialise and deserialise is allowed, and for the local |
291 | that Storable can serialise and deserialise is allowed, and for the local |
299 | node, anything can be passed. |
292 | node, anything can be passed. Best rely only on the common denominator of |
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293 | these. |
300 | |
294 | |
301 | =item $local_port = port |
295 | =item $local_port = port |
302 | |
296 | |
303 | Create a new local port object and returns its port ID. Initially it has |
297 | Create a new local port object and returns its port ID. Initially it has |
304 | no callbacks set and will throw an error when it receives messages. |
298 | no callbacks set and will throw an error when it receives messages. |
… | |
… | |
351 | The default callback received all messages not matched by a more specific |
345 | The default callback received all messages not matched by a more specific |
352 | C<tag> match. |
346 | C<tag> match. |
353 | |
347 | |
354 | =item rcv $local_port, tag => $callback->(@msg_without_tag), ... |
348 | =item rcv $local_port, tag => $callback->(@msg_without_tag), ... |
355 | |
349 | |
356 | Register callbacks to be called on messages starting with the given tag on |
350 | Register (or replace) callbacks to be called on messages starting with the |
357 | the given port (and return the port), or unregister it (when C<$callback> |
351 | given tag on the given port (and return the port), or unregister it (when |
358 | is C<$undef>). |
352 | C<$callback> is C<$undef> or missing). There can only be one callback |
|
|
353 | registered for each tag. |
359 | |
354 | |
360 | The original message will be passed to the callback, after the first |
355 | The original message will be passed to the callback, after the first |
361 | element (the tag) has been removed. The callback will use the same |
356 | element (the tag) has been removed. The callback will use the same |
362 | environment as the default callback (see above). |
357 | environment as the default callback (see above). |
363 | |
358 | |
… | |
… | |
375 | rcv port, |
370 | rcv port, |
376 | msg1 => sub { ... }, |
371 | msg1 => sub { ... }, |
377 | ... |
372 | ... |
378 | ; |
373 | ; |
379 | |
374 | |
|
|
375 | Example: temporarily register a rcv callback for a tag matching some port |
|
|
376 | (e.g. for a rpc reply) and unregister it after a message was received. |
|
|
377 | |
|
|
378 | rcv $port, $otherport => sub { |
|
|
379 | my @reply = @_; |
|
|
380 | |
|
|
381 | rcv $SELF, $otherport; |
|
|
382 | }; |
|
|
383 | |
380 | =cut |
384 | =cut |
381 | |
385 | |
382 | sub rcv($@) { |
386 | sub rcv($@) { |
383 | my $port = shift; |
387 | my $port = shift; |
384 | my ($noderef, $portid) = split /#/, $port, 2; |
388 | my ($nodeid, $portid) = split /#/, $port, 2; |
385 | |
389 | |
386 | ($NODE{$noderef} || add_node $noderef) == $NODE{""} |
390 | $NODE{$nodeid} == $NODE{""} |
387 | or Carp::croak "$port: rcv can only be called on local ports, caught"; |
391 | or Carp::croak "$port: rcv can only be called on local ports, caught"; |
388 | |
392 | |
389 | while (@_) { |
393 | while (@_) { |
390 | if (ref $_[0]) { |
394 | if (ref $_[0]) { |
391 | if (my $self = $PORT_DATA{$portid}) { |
395 | if (my $self = $PORT_DATA{$portid}) { |
… | |
… | |
470 | $res |
474 | $res |
471 | } |
475 | } |
472 | } |
476 | } |
473 | } |
477 | } |
474 | |
478 | |
475 | =item $guard = mon $port, $cb->(@reason) |
479 | =item $guard = mon $port, $cb->(@reason) # call $cb when $port dies |
476 | |
480 | |
477 | =item $guard = mon $port, $rcvport |
481 | =item $guard = mon $port, $rcvport # kill $rcvport when $port dies |
478 | |
482 | |
479 | =item $guard = mon $port |
483 | =item $guard = mon $port # kill $SELF when $port dies |
480 | |
484 | |
481 | =item $guard = mon $port, $rcvport, @msg |
485 | =item $guard = mon $port, $rcvport, @msg # send a message when $port dies |
482 | |
486 | |
483 | Monitor the given port and do something when the port is killed or |
487 | Monitor the given port and do something when the port is killed or |
484 | messages to it were lost, and optionally return a guard that can be used |
488 | messages to it were lost, and optionally return a guard that can be used |
485 | to stop monitoring again. |
489 | to stop monitoring again. |
486 | |
|
|
487 | C<mon> effectively guarantees that, in the absence of hardware failures, |
|
|
488 | that after starting the monitor, either all messages sent to the port |
|
|
489 | will arrive, or the monitoring action will be invoked after possible |
|
|
490 | message loss has been detected. No messages will be lost "in between" |
|
|
491 | (after the first lost message no further messages will be received by the |
|
|
492 | port). After the monitoring action was invoked, further messages might get |
|
|
493 | delivered again. |
|
|
494 | |
490 | |
495 | In the first form (callback), the callback is simply called with any |
491 | In the first form (callback), the callback is simply called with any |
496 | number of C<@reason> elements (no @reason means that the port was deleted |
492 | number of C<@reason> elements (no @reason means that the port was deleted |
497 | "normally"). Note also that I<< the callback B<must> never die >>, so use |
493 | "normally"). Note also that I<< the callback B<must> never die >>, so use |
498 | C<eval> if unsure. |
494 | C<eval> if unsure. |
499 | |
495 | |
500 | In the second form (another port given), the other port (C<$rcvport>) |
496 | In the second form (another port given), the other port (C<$rcvport>) |
501 | will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on |
497 | will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on |
502 | "normal" kils nothing happens, while under all other conditions, the other |
498 | "normal" kils nothing happens, while under all other conditions, the other |
503 | port is killed with the same reason. |
499 | port is killed with the same reason. |
504 | |
500 | |
505 | The third form (kill self) is the same as the second form, except that |
501 | The third form (kill self) is the same as the second form, except that |
506 | C<$rvport> defaults to C<$SELF>. |
502 | C<$rvport> defaults to C<$SELF>. |
507 | |
503 | |
508 | In the last form (message), a message of the form C<@msg, @reason> will be |
504 | In the last form (message), a message of the form C<@msg, @reason> will be |
509 | C<snd>. |
505 | C<snd>. |
|
|
506 | |
|
|
507 | Monitoring-actions are one-shot: once messages are lost (and a monitoring |
|
|
508 | alert was raised), they are removed and will not trigger again. |
510 | |
509 | |
511 | As a rule of thumb, monitoring requests should always monitor a port from |
510 | As a rule of thumb, monitoring requests should always monitor a port from |
512 | a local port (or callback). The reason is that kill messages might get |
511 | a local port (or callback). The reason is that kill messages might get |
513 | lost, just like any other message. Another less obvious reason is that |
512 | lost, just like any other message. Another less obvious reason is that |
514 | even monitoring requests can get lost (for exmaple, when the connection |
513 | even monitoring requests can get lost (for example, when the connection |
515 | to the other node goes down permanently). When monitoring a port locally |
514 | to the other node goes down permanently). When monitoring a port locally |
516 | these problems do not exist. |
515 | these problems do not exist. |
517 | |
516 | |
|
|
517 | C<mon> effectively guarantees that, in the absence of hardware failures, |
|
|
518 | after starting the monitor, either all messages sent to the port will |
|
|
519 | arrive, or the monitoring action will be invoked after possible message |
|
|
520 | loss has been detected. No messages will be lost "in between" (after |
|
|
521 | the first lost message no further messages will be received by the |
|
|
522 | port). After the monitoring action was invoked, further messages might get |
|
|
523 | delivered again. |
|
|
524 | |
|
|
525 | Inter-host-connection timeouts and monitoring depend on the transport |
|
|
526 | used. The only transport currently implemented is TCP, and AnyEvent::MP |
|
|
527 | relies on TCP to detect node-downs (this can take 10-15 minutes on a |
|
|
528 | non-idle connection, and usually around two hours for idle conenctions). |
|
|
529 | |
|
|
530 | This means that monitoring is good for program errors and cleaning up |
|
|
531 | stuff eventually, but they are no replacement for a timeout when you need |
|
|
532 | to ensure some maximum latency. |
|
|
533 | |
518 | Example: call a given callback when C<$port> is killed. |
534 | Example: call a given callback when C<$port> is killed. |
519 | |
535 | |
520 | mon $port, sub { warn "port died because of <@_>\n" }; |
536 | mon $port, sub { warn "port died because of <@_>\n" }; |
521 | |
537 | |
522 | Example: kill ourselves when C<$port> is killed abnormally. |
538 | Example: kill ourselves when C<$port> is killed abnormally. |
… | |
… | |
528 | mon $port, $self => "restart"; |
544 | mon $port, $self => "restart"; |
529 | |
545 | |
530 | =cut |
546 | =cut |
531 | |
547 | |
532 | sub mon { |
548 | sub mon { |
533 | my ($noderef, $port) = split /#/, shift, 2; |
549 | my ($nodeid, $port) = split /#/, shift, 2; |
534 | |
550 | |
535 | my $node = $NODE{$noderef} || add_node $noderef; |
551 | my $node = $NODE{$nodeid} || add_node $nodeid; |
536 | |
552 | |
537 | my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; |
553 | my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; |
538 | |
554 | |
539 | unless (ref $cb) { |
555 | unless (ref $cb) { |
540 | if (@_) { |
556 | if (@_) { |
… | |
… | |
560 | is killed, the references will be freed. |
576 | is killed, the references will be freed. |
561 | |
577 | |
562 | Optionally returns a guard that will stop the monitoring. |
578 | Optionally returns a guard that will stop the monitoring. |
563 | |
579 | |
564 | This function is useful when you create e.g. timers or other watchers and |
580 | This function is useful when you create e.g. timers or other watchers and |
565 | want to free them when the port gets killed: |
581 | want to free them when the port gets killed (note the use of C<psub>): |
566 | |
582 | |
567 | $port->rcv (start => sub { |
583 | $port->rcv (start => sub { |
568 | my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { |
584 | my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub { |
569 | undef $timer if 0.9 < rand; |
585 | undef $timer if 0.9 < rand; |
570 | }); |
586 | }); |
571 | }); |
587 | }); |
572 | |
588 | |
573 | =cut |
589 | =cut |
… | |
… | |
582 | |
598 | |
583 | =item kil $port[, @reason] |
599 | =item kil $port[, @reason] |
584 | |
600 | |
585 | Kill the specified port with the given C<@reason>. |
601 | Kill the specified port with the given C<@reason>. |
586 | |
602 | |
587 | If no C<@reason> is specified, then the port is killed "normally" (linked |
603 | If no C<@reason> is specified, then the port is killed "normally" (ports |
588 | ports will not be kileld, or even notified). |
604 | monitoring other ports will not necessarily die because a port dies |
|
|
605 | "normally"). |
589 | |
606 | |
590 | Otherwise, linked ports get killed with the same reason (second form of |
607 | Otherwise, linked ports get killed with the same reason (second form of |
591 | C<mon>, see below). |
608 | C<mon>, see above). |
592 | |
609 | |
593 | Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks |
610 | Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks |
594 | will be reported as reason C<< die => $@ >>. |
611 | will be reported as reason C<< die => $@ >>. |
595 | |
612 | |
596 | Transport/communication errors are reported as C<< transport_error => |
613 | Transport/communication errors are reported as C<< transport_error => |
… | |
… | |
601 | =item $port = spawn $node, $initfunc[, @initdata] |
618 | =item $port = spawn $node, $initfunc[, @initdata] |
602 | |
619 | |
603 | Creates a port on the node C<$node> (which can also be a port ID, in which |
620 | Creates a port on the node C<$node> (which can also be a port ID, in which |
604 | case it's the node where that port resides). |
621 | case it's the node where that port resides). |
605 | |
622 | |
606 | The port ID of the newly created port is return immediately, and it is |
623 | The port ID of the newly created port is returned immediately, and it is |
607 | permissible to immediately start sending messages or monitor the port. |
624 | possible to immediately start sending messages or to monitor the port. |
608 | |
625 | |
609 | After the port has been created, the init function is |
626 | After the port has been created, the init function is called on the remote |
610 | called. This function must be a fully-qualified function name |
627 | node, in the same context as a C<rcv> callback. This function must be a |
611 | (e.g. C<MyApp::Chat::Server::init>). To specify a function in the main |
628 | fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To |
612 | program, use C<::name>. |
629 | specify a function in the main program, use C<::name>. |
613 | |
630 | |
614 | If the function doesn't exist, then the node tries to C<require> |
631 | If the function doesn't exist, then the node tries to C<require> |
615 | the package, then the package above the package and so on (e.g. |
632 | the package, then the package above the package and so on (e.g. |
616 | C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function |
633 | C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function |
617 | exists or it runs out of package names. |
634 | exists or it runs out of package names. |
618 | |
635 | |
619 | The init function is then called with the newly-created port as context |
636 | The init function is then called with the newly-created port as context |
620 | object (C<$SELF>) and the C<@initdata> values as arguments. |
637 | object (C<$SELF>) and the C<@initdata> values as arguments. It I<must> |
|
|
638 | call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise |
|
|
639 | the port might not get created. |
621 | |
640 | |
622 | A common idiom is to pass your own port, monitor the spawned port, and |
641 | A common idiom is to pass a local port, immediately monitor the spawned |
623 | in the init function, monitor the original port. This two-way monitoring |
642 | port, and in the remote init function, immediately monitor the passed |
624 | ensures that both ports get cleaned up when there is a problem. |
643 | local port. This two-way monitoring ensures that both ports get cleaned up |
|
|
644 | when there is a problem. |
|
|
645 | |
|
|
646 | C<spawn> guarantees that the C<$initfunc> has no visible effects on the |
|
|
647 | caller before C<spawn> returns (by delaying invocation when spawn is |
|
|
648 | called for the local node). |
625 | |
649 | |
626 | Example: spawn a chat server port on C<$othernode>. |
650 | Example: spawn a chat server port on C<$othernode>. |
627 | |
651 | |
628 | # this node, executed from within a port context: |
652 | # this node, executed from within a port context: |
629 | my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; |
653 | my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; |
… | |
… | |
644 | |
668 | |
645 | sub _spawn { |
669 | sub _spawn { |
646 | my $port = shift; |
670 | my $port = shift; |
647 | my $init = shift; |
671 | my $init = shift; |
648 | |
672 | |
|
|
673 | # rcv will create the actual port |
649 | local $SELF = "$NODE#$port"; |
674 | local $SELF = "$NODE#$port"; |
650 | eval { |
675 | eval { |
651 | &{ load_func $init } |
676 | &{ load_func $init } |
652 | }; |
677 | }; |
653 | _self_die if $@; |
678 | _self_die if $@; |
654 | } |
679 | } |
655 | |
680 | |
656 | sub spawn(@) { |
681 | sub spawn(@) { |
657 | my ($noderef, undef) = split /#/, shift, 2; |
682 | my ($nodeid, undef) = split /#/, shift, 2; |
658 | |
683 | |
659 | my $id = "$RUNIQ." . $ID++; |
684 | my $id = "$RUNIQ." . $ID++; |
660 | |
685 | |
661 | $_[0] =~ /::/ |
686 | $_[0] =~ /::/ |
662 | or Carp::croak "spawn init function must be a fully-qualified name, caught"; |
687 | or Carp::croak "spawn init function must be a fully-qualified name, caught"; |
663 | |
688 | |
664 | ($NODE{$noderef} || add_node $noderef) |
689 | snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_; |
665 | ->send (["", "AnyEvent::MP::_spawn" => $id, @_]); |
|
|
666 | |
690 | |
667 | "$noderef#$id" |
691 | "$nodeid#$id" |
668 | } |
692 | } |
669 | |
693 | |
670 | =back |
694 | =item after $timeout, @msg |
671 | |
695 | |
672 | =head1 NODE MESSAGES |
696 | =item after $timeout, $callback |
673 | |
697 | |
674 | Nodes understand the following messages sent to them. Many of them take |
698 | Either sends the given message, or call the given callback, after the |
675 | arguments called C<@reply>, which will simply be used to compose a reply |
699 | specified number of seconds. |
676 | message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and |
|
|
677 | the remaining arguments are simply the message data. |
|
|
678 | |
700 | |
679 | While other messages exist, they are not public and subject to change. |
701 | This is simply a utility function that comes in handy at times - the |
|
|
702 | AnyEvent::MP author is not convinced of the wisdom of having it, though, |
|
|
703 | so it may go away in the future. |
680 | |
704 | |
681 | =over 4 |
|
|
682 | |
|
|
683 | =cut |
705 | =cut |
684 | |
706 | |
685 | =item lookup => $name, @reply |
707 | sub after($@) { |
|
|
708 | my ($timeout, @action) = @_; |
686 | |
709 | |
687 | Replies with the port ID of the specified well-known port, or C<undef>. |
710 | my $t; $t = AE::timer $timeout, 0, sub { |
|
|
711 | undef $t; |
|
|
712 | ref $action[0] |
|
|
713 | ? $action[0]() |
|
|
714 | : snd @action; |
|
|
715 | }; |
|
|
716 | } |
688 | |
717 | |
689 | =item devnull => ... |
718 | =item cal $port, @msg, $callback[, $timeout] |
690 | |
719 | |
691 | Generic data sink/CPU heat conversion. |
720 | A simple form of RPC - sends a message to the given C<$port> with the |
|
|
721 | given contents (C<@msg>), but adds a reply port to the message. |
692 | |
722 | |
693 | =item relay => $port, @msg |
723 | The reply port is created temporarily just for the purpose of receiving |
|
|
724 | the reply, and will be C<kil>ed when no longer needed. |
694 | |
725 | |
695 | Simply forwards the message to the given port. |
726 | A reply message sent to the port is passed to the C<$callback> as-is. |
696 | |
727 | |
697 | =item eval => $string[ @reply] |
728 | If an optional time-out (in seconds) is given and it is not C<undef>, |
|
|
729 | then the callback will be called without any arguments after the time-out |
|
|
730 | elapsed and the port is C<kil>ed. |
698 | |
731 | |
699 | Evaluates the given string. If C<@reply> is given, then a message of the |
732 | If no time-out is given, then the local port will monitor the remote port |
700 | form C<@reply, $@, @evalres> is sent. |
733 | instead, so it eventually gets cleaned-up. |
701 | |
734 | |
702 | Example: crash another node. |
735 | Currently this function returns the temporary port, but this "feature" |
|
|
736 | might go in future versions unless you can make a convincing case that |
|
|
737 | this is indeed useful for something. |
703 | |
738 | |
704 | snd $othernode, eval => "exit"; |
739 | =cut |
705 | |
740 | |
706 | =item time => @reply |
741 | sub cal(@) { |
|
|
742 | my $timeout = ref $_[-1] ? undef : pop; |
|
|
743 | my $cb = pop; |
707 | |
744 | |
708 | Replies the the current node time to C<@reply>. |
745 | my $port = port { |
|
|
746 | undef $timeout; |
|
|
747 | kil $SELF; |
|
|
748 | &$cb; |
|
|
749 | }; |
709 | |
750 | |
710 | Example: tell the current node to send the current time to C<$myport> in a |
751 | if (defined $timeout) { |
711 | C<timereply> message. |
752 | $timeout = AE::timer $timeout, 0, sub { |
|
|
753 | undef $timeout; |
|
|
754 | kil $port; |
|
|
755 | $cb->(); |
|
|
756 | }; |
|
|
757 | } else { |
|
|
758 | mon $_[0], sub { |
|
|
759 | kil $port; |
|
|
760 | $cb->(); |
|
|
761 | }; |
|
|
762 | } |
712 | |
763 | |
713 | snd $NODE, time => $myport, timereply => 1, 2; |
764 | push @_, $port; |
714 | # => snd $myport, timereply => 1, 2, <time> |
765 | &snd; |
|
|
766 | |
|
|
767 | $port |
|
|
768 | } |
715 | |
769 | |
716 | =back |
770 | =back |
717 | |
771 | |
718 | =head1 AnyEvent::MP vs. Distributed Erlang |
772 | =head1 AnyEvent::MP vs. Distributed Erlang |
719 | |
773 | |
… | |
… | |
729 | |
783 | |
730 | Despite the similarities, there are also some important differences: |
784 | Despite the similarities, there are also some important differences: |
731 | |
785 | |
732 | =over 4 |
786 | =over 4 |
733 | |
787 | |
734 | =item * Node references contain the recipe on how to contact them. |
788 | =item * Node IDs are arbitrary strings in AEMP. |
735 | |
789 | |
736 | Erlang relies on special naming and DNS to work everywhere in the |
790 | Erlang relies on special naming and DNS to work everywhere in the same |
737 | same way. AEMP relies on each node knowing it's own address(es), with |
791 | way. AEMP relies on each node somehow knowing its own address(es) (e.g. by |
738 | convenience functionality. |
792 | configuration or DNS), but will otherwise discover other odes itself. |
739 | |
793 | |
740 | This means that AEMP requires a less tightly controlled environment at the |
|
|
741 | cost of longer node references and a slightly higher management overhead. |
|
|
742 | |
|
|
743 | =item Erlang has a "remote ports are like local ports" philosophy, AEMP |
794 | =item * Erlang has a "remote ports are like local ports" philosophy, AEMP |
744 | uses "local ports are like remote ports". |
795 | uses "local ports are like remote ports". |
745 | |
796 | |
746 | The failure modes for local ports are quite different (runtime errors |
797 | The failure modes for local ports are quite different (runtime errors |
747 | only) then for remote ports - when a local port dies, you I<know> it dies, |
798 | only) then for remote ports - when a local port dies, you I<know> it dies, |
748 | when a connection to another node dies, you know nothing about the other |
799 | when a connection to another node dies, you know nothing about the other |
… | |
… | |
759 | |
810 | |
760 | Erlang uses processes that selectively receive messages, and therefore |
811 | Erlang uses processes that selectively receive messages, and therefore |
761 | needs a queue. AEMP is event based, queuing messages would serve no |
812 | needs a queue. AEMP is event based, queuing messages would serve no |
762 | useful purpose. For the same reason the pattern-matching abilities of |
813 | useful purpose. For the same reason the pattern-matching abilities of |
763 | AnyEvent::MP are more limited, as there is little need to be able to |
814 | AnyEvent::MP are more limited, as there is little need to be able to |
764 | filter messages without dequeing them. |
815 | filter messages without dequeuing them. |
765 | |
816 | |
766 | (But see L<Coro::MP> for a more Erlang-like process model on top of AEMP). |
817 | (But see L<Coro::MP> for a more Erlang-like process model on top of AEMP). |
767 | |
818 | |
768 | =item * Erlang sends are synchronous, AEMP sends are asynchronous. |
819 | =item * Erlang sends are synchronous, AEMP sends are asynchronous. |
769 | |
820 | |
… | |
… | |
775 | |
826 | |
776 | Erlang makes few guarantees on messages delivery - messages can get lost |
827 | Erlang makes few guarantees on messages delivery - messages can get lost |
777 | without any of the processes realising it (i.e. you send messages a, b, |
828 | without any of the processes realising it (i.e. you send messages a, b, |
778 | and c, and the other side only receives messages a and c). |
829 | and c, and the other side only receives messages a and c). |
779 | |
830 | |
780 | AEMP guarantees correct ordering, and the guarantee that there are no |
831 | AEMP guarantees correct ordering, and the guarantee that after one message |
781 | holes in the message sequence. |
832 | is lost, all following ones sent to the same port are lost as well, until |
782 | |
833 | monitoring raises an error, so there are no silent "holes" in the message |
783 | =item * In Erlang, processes can be declared dead and later be found to be |
834 | sequence. |
784 | alive. |
|
|
785 | |
|
|
786 | In Erlang it can happen that a monitored process is declared dead and |
|
|
787 | linked processes get killed, but later it turns out that the process is |
|
|
788 | still alive - and can receive messages. |
|
|
789 | |
|
|
790 | In AEMP, when port monitoring detects a port as dead, then that port will |
|
|
791 | eventually be killed - it cannot happen that a node detects a port as dead |
|
|
792 | and then later sends messages to it, finding it is still alive. |
|
|
793 | |
835 | |
794 | =item * Erlang can send messages to the wrong port, AEMP does not. |
836 | =item * Erlang can send messages to the wrong port, AEMP does not. |
795 | |
837 | |
796 | In Erlang it is quite likely that a node that restarts reuses a process ID |
838 | In Erlang it is quite likely that a node that restarts reuses a process ID |
797 | known to other nodes for a completely different process, causing messages |
839 | known to other nodes for a completely different process, causing messages |
… | |
… | |
801 | around in the network will not be sent to an unrelated port. |
843 | around in the network will not be sent to an unrelated port. |
802 | |
844 | |
803 | =item * Erlang uses unprotected connections, AEMP uses secure |
845 | =item * Erlang uses unprotected connections, AEMP uses secure |
804 | authentication and can use TLS. |
846 | authentication and can use TLS. |
805 | |
847 | |
806 | AEMP can use a proven protocol - SSL/TLS - to protect connections and |
848 | AEMP can use a proven protocol - TLS - to protect connections and |
807 | securely authenticate nodes. |
849 | securely authenticate nodes. |
808 | |
850 | |
809 | =item * The AEMP protocol is optimised for both text-based and binary |
851 | =item * The AEMP protocol is optimised for both text-based and binary |
810 | communications. |
852 | communications. |
811 | |
853 | |
812 | The AEMP protocol, unlike the Erlang protocol, supports both |
854 | The AEMP protocol, unlike the Erlang protocol, supports both programming |
813 | language-independent text-only protocols (good for debugging) and binary, |
855 | language independent text-only protocols (good for debugging) and binary, |
814 | language-specific serialisers (e.g. Storable). |
856 | language-specific serialisers (e.g. Storable). By default, unless TLS is |
|
|
857 | used, the protocol is actually completely text-based. |
815 | |
858 | |
816 | It has also been carefully designed to be implementable in other languages |
859 | It has also been carefully designed to be implementable in other languages |
817 | with a minimum of work while gracefully degrading fucntionality to make the |
860 | with a minimum of work while gracefully degrading functionality to make the |
818 | protocol simple. |
861 | protocol simple. |
819 | |
862 | |
820 | =item * AEMP has more flexible monitoring options than Erlang. |
863 | =item * AEMP has more flexible monitoring options than Erlang. |
821 | |
864 | |
822 | In Erlang, you can chose to receive I<all> exit signals as messages |
865 | In Erlang, you can chose to receive I<all> exit signals as messages |
… | |
… | |
825 | Erlang, as one can choose between automatic kill, exit message or callback |
868 | Erlang, as one can choose between automatic kill, exit message or callback |
826 | on a per-process basis. |
869 | on a per-process basis. |
827 | |
870 | |
828 | =item * Erlang tries to hide remote/local connections, AEMP does not. |
871 | =item * Erlang tries to hide remote/local connections, AEMP does not. |
829 | |
872 | |
830 | Monitoring in Erlang is not an indicator of process death/crashes, |
873 | Monitoring in Erlang is not an indicator of process death/crashes, in the |
831 | as linking is (except linking is unreliable in Erlang). |
874 | same way as linking is (except linking is unreliable in Erlang). |
832 | |
875 | |
833 | In AEMP, you don't "look up" registered port names or send to named ports |
876 | In AEMP, you don't "look up" registered port names or send to named ports |
834 | that might or might not be persistent. Instead, you normally spawn a port |
877 | that might or might not be persistent. Instead, you normally spawn a port |
835 | on the remote node. The init function monitors the you, and you monitor |
878 | on the remote node. The init function monitors you, and you monitor the |
836 | the remote port. Since both monitors are local to the node, they are much |
879 | remote port. Since both monitors are local to the node, they are much more |
837 | more reliable. |
880 | reliable (no need for C<spawn_link>). |
838 | |
881 | |
839 | This also saves round-trips and avoids sending messages to the wrong port |
882 | This also saves round-trips and avoids sending messages to the wrong port |
840 | (hard to do in Erlang). |
883 | (hard to do in Erlang). |
841 | |
884 | |
842 | =back |
885 | =back |
843 | |
886 | |
844 | =head1 RATIONALE |
887 | =head1 RATIONALE |
845 | |
888 | |
846 | =over 4 |
889 | =over 4 |
847 | |
890 | |
848 | =item Why strings for ports and noderefs, why not objects? |
891 | =item Why strings for port and node IDs, why not objects? |
849 | |
892 | |
850 | We considered "objects", but found that the actual number of methods |
893 | We considered "objects", but found that the actual number of methods |
851 | thatc an be called are very low. Since port IDs and noderefs travel over |
894 | that can be called are quite low. Since port and node IDs travel over |
852 | the network frequently, the serialising/deserialising would add lots of |
895 | the network frequently, the serialising/deserialising would add lots of |
853 | overhead, as well as having to keep a proxy object. |
896 | overhead, as well as having to keep a proxy object everywhere. |
854 | |
897 | |
855 | Strings can easily be printed, easily serialised etc. and need no special |
898 | Strings can easily be printed, easily serialised etc. and need no special |
856 | procedures to be "valid". |
899 | procedures to be "valid". |
857 | |
900 | |
858 | And a a miniport consists of a single closure stored in a global hash - it |
901 | And as a result, a miniport consists of a single closure stored in a |
859 | can't become much cheaper. |
902 | global hash - it can't become much cheaper. |
860 | |
903 | |
861 | =item Why favour JSON, why not real serialising format such as Storable? |
904 | =item Why favour JSON, why not a real serialising format such as Storable? |
862 | |
905 | |
863 | In fact, any AnyEvent::MP node will happily accept Storable as framing |
906 | In fact, any AnyEvent::MP node will happily accept Storable as framing |
864 | format, but currently there is no way to make a node use Storable by |
907 | format, but currently there is no way to make a node use Storable by |
865 | default. |
908 | default (although all nodes will accept it). |
866 | |
909 | |
867 | The default framing protocol is JSON because a) JSON::XS is many times |
910 | The default framing protocol is JSON because a) JSON::XS is many times |
868 | faster for small messages and b) most importantly, after years of |
911 | faster for small messages and b) most importantly, after years of |
869 | experience we found that object serialisation is causing more problems |
912 | experience we found that object serialisation is causing more problems |
870 | than it gains: Just like function calls, objects simply do not travel |
913 | than it solves: Just like function calls, objects simply do not travel |
871 | easily over the network, mostly because they will always be a copy, so you |
914 | easily over the network, mostly because they will always be a copy, so you |
872 | always have to re-think your design. |
915 | always have to re-think your design. |
873 | |
916 | |
874 | Keeping your messages simple, concentrating on data structures rather than |
917 | Keeping your messages simple, concentrating on data structures rather than |
875 | objects, will keep your messages clean, tidy and efficient. |
918 | objects, will keep your messages clean, tidy and efficient. |
876 | |
919 | |
877 | =back |
920 | =back |
878 | |
921 | |
879 | =head1 SEE ALSO |
922 | =head1 SEE ALSO |
880 | |
923 | |
|
|
924 | L<AnyEvent::MP::Intro> - a gentle introduction. |
|
|
925 | |
|
|
926 | L<AnyEvent::MP::Kernel> - more, lower-level, stuff. |
|
|
927 | |
|
|
928 | L<AnyEvent::MP::Global> - network maintainance and port groups, to find |
|
|
929 | your applications. |
|
|
930 | |
|
|
931 | L<AnyEvent::MP::LogCatcher> - simple service to display log messages from |
|
|
932 | all nodes. |
|
|
933 | |
881 | L<AnyEvent>. |
934 | L<AnyEvent>. |
882 | |
935 | |
883 | =head1 AUTHOR |
936 | =head1 AUTHOR |
884 | |
937 | |
885 | Marc Lehmann <schmorp@schmorp.de> |
938 | Marc Lehmann <schmorp@schmorp.de> |