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Revision 1.128 by root, Sun Mar 4 14:28:44 2012 UTC

1=head1 NAME 1=head1 NAME
2 2
3AnyEvent::MP - multi-processing/message-passing framework 3AnyEvent::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
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; 15 configure;
17 16
18 # ports are message endpoints 17 # ports are message destinations
19 18
20 # sending messages 19 # sending messages
21 snd $port, type => data...; 20 snd $port, type => data...;
22 snd $port, @msg; 21 snd $port, @msg;
23 snd @msg_with_first_element_being_a_port; 22 snd @msg_with_first_element_being_a_port;
24 23
25 # creating/using ports, the simple way 24 # creating/using ports, the simple way
26 my $simple_port = port { my @msg = @_; 0 }; 25 my $simple_port = port { my @msg = @_ };
27 26
28 # creating/using ports, tagged message matching 27 # creating/using ports, tagged message matching
29 my $port = port; 28 my $port = port;
30 rcv $port, ping => sub { snd $_[0], "pong"; 0 }; 29 rcv $port, ping => sub { snd $_[0], "pong" };
31 rcv $port, pong => sub { warn "pong received\n"; 0 }; 30 rcv $port, pong => sub { warn "pong received\n" };
32 31
33 # create a port on another node 32 # create a port on another node
34 my $port = spawn $node, $initfunc, @initdata; 33 my $port = spawn $node, $initfunc, @initdata;
35 34
35 # destroy a port again
36 kil $port; # "normal" kill
37 kil $port, my_error => "everything is broken"; # error kill
38
36 # monitoring 39 # monitoring
37 mon $port, $cb->(@msg) # callback is invoked on death 40 mon $localport, $cb->(@msg) # callback is invoked on death
38 mon $port, $otherport # kill otherport on abnormal death 41 mon $localport, $otherport # kill otherport on abnormal death
39 mon $port, $otherport, @msg # send message on death 42 mon $localport, $otherport, @msg # send message on death
43
44 # temporarily execute code in port context
45 peval $port, sub { die "kill the port!" };
46
47 # execute callbacks in $SELF port context
48 my $timer = AE::timer 1, 0, psub {
49 die "kill the port, delayed";
50 };
40 51
41=head1 CURRENT STATUS 52=head1 CURRENT STATUS
42 53
54 bin/aemp - stable.
43 AnyEvent::MP - stable API, should work 55 AnyEvent::MP - stable API, should work.
44 AnyEvent::MP::Intro - outdated 56 AnyEvent::MP::Intro - explains most concepts.
45 AnyEvent::MP::Kernel - mostly stable 57 AnyEvent::MP::Kernel - mostly stable API.
46 AnyEvent::MP::Global - mostly stable 58 AnyEvent::MP::Global - stable API.
47 AnyEvent::MP::Node - mostly stable, but internal anyways
48 AnyEvent::MP::Transport - mostly stable, but internal anyways
49
50 stay tuned.
51 59
52=head1 DESCRIPTION 60=head1 DESCRIPTION
53 61
54This module (-family) implements a simple message passing framework. 62This module (-family) implements a simple message passing framework.
55 63
57on the same or other hosts, and you can supervise entities remotely. 65on the same or other hosts, and you can supervise entities remotely.
58 66
59For an introduction to this module family, see the L<AnyEvent::MP::Intro> 67For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60manual page and the examples under F<eg/>. 68manual page and the examples under F<eg/>.
61 69
62At the moment, this module family is a bit underdocumented.
63
64=head1 CONCEPTS 70=head1 CONCEPTS
65 71
66=over 4 72=over 4
67 73
68=item port 74=item port
69 75
70A port is something you can send messages to (with the C<snd> function). 76Not to be confused with a TCP port, a "port" is something you can send
77messages to (with the C<snd> function).
71 78
72Ports allow you to register C<rcv> handlers that can match all or just 79Ports allow you to register C<rcv> handlers that can match all or just
73some messages. Messages send to ports will not be queued, regardless of 80some messages. Messages send to ports will not be queued, regardless of
74anything was listening for them or not. 81anything was listening for them or not.
75 82
83Ports are represented by (printable) strings called "port IDs".
84
76=item port ID - C<nodeid#portname> 85=item port ID - C<nodeid#portname>
77 86
78A port ID is the concatenation of a node ID, a hash-mark (C<#>) as 87A port ID is the concatenation of a node ID, a hash-mark (C<#>)
79separator, and a port name (a printable string of unspecified format). 88as separator, and a port name (a printable string of unspecified
89format created by AnyEvent::MP).
80 90
81=item node 91=item node
82 92
83A node is a single process containing at least one port - the node port, 93A node is a single process containing at least one port - the node port,
84which enables nodes to manage each other remotely, and to create new 94which enables nodes to manage each other remotely, and to create new
85ports. 95ports.
86 96
87Nodes are either public (have one or more listening ports) or private 97Nodes are either public (have one or more listening ports) or private
88(no listening ports). Private nodes cannot talk to other private nodes 98(no listening ports). Private nodes cannot talk to other private nodes
89currently. 99currently, but all nodes can talk to public nodes.
90 100
101Nodes is represented by (printable) strings called "node IDs".
102
91=item node ID - C<[a-za-Z0-9_\-.:]+> 103=item node ID - C<[A-Za-z0-9_\-.:]*>
92 104
93A node ID is a string that uniquely identifies the node within a 105A node ID is a string that uniquely identifies the node within a
94network. Depending on the configuration used, node IDs can look like a 106network. Depending on the configuration used, node IDs can look like a
95hostname, a hostname and a port, or a random string. AnyEvent::MP itself 107hostname, a hostname and a port, or a random string. AnyEvent::MP itself
96doesn't interpret node IDs in any way. 108doesn't interpret node IDs in any way except to uniquely identify a node.
97 109
98=item binds - C<ip:port> 110=item binds - C<ip:port>
99 111
100Nodes can only talk to each other by creating some kind of connection to 112Nodes can only talk to each other by creating some kind of connection to
101each other. To do this, nodes should listen on one or more local transport 113each other. To do this, nodes should listen on one or more local transport
114endpoints - binds.
115
102endpoints - binds. Currently, only standard C<ip:port> specifications can 116Currently, only standard C<ip:port> specifications can be used, which
103be used, which specify TCP ports to listen on. 117specify TCP ports to listen on. So a bind is basically just a tcp socket
118in listening mode thta accepts conenctions form other nodes.
104 119
120=item seed nodes
121
122When a node starts, it knows nothing about the network it is in - it
123needs to connect to at least one other node that is already in the
124network. These other nodes are called "seed nodes".
125
126Seed nodes themselves are not special - they are seed nodes only because
127some other node I<uses> them as such, but any node can be used as seed
128node for other nodes, and eahc node cna use a different set of seed nodes.
129
130In addition to discovering the network, seed nodes are also used to
131maintain the network - all nodes using the same seed node form are part of
132the same network. If a network is split into multiple subnets because e.g.
133the network link between the parts goes down, then using the same seed
134nodes for all nodes ensures that eventually the subnets get merged again.
135
136Seed nodes are expected to be long-running, and at least one seed node
137should always be available. They should also be relatively responsive - a
138seed node that blocks for long periods will slow down everybody else.
139
140For small networks, it's best if every node uses the same set of seed
141nodes. For large networks, it can be useful to specify "regional" seed
142nodes for most nodes in an area, and use all seed nodes as seed nodes for
143each other. What's important is that all seed nodes connections form a
144complete graph, so that the network cannot split into separate subnets
145forever.
146
147Seed nodes are represented by seed IDs.
148
105=item seeds - C<host:port> 149=item seed IDs - C<host:port>
106 150
107When a node starts, it knows nothing about the network. To teach the node 151Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
108about the network it first has to contact some other node within the 152TCP port) of nodes that should be used as seed nodes.
109network. This node is called a seed.
110 153
111Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes 154=item global nodes
112are expected to be long-running, and at least one of those should always
113be available. When nodes run out of connections (e.g. due to a network
114error), they try to re-establish connections to some seednodes again to
115join the network.
116 155
117Apart from being sued for seeding, seednodes are not special in any way - 156An AEMP network needs a discovery service - nodes need to know how to
118every public node can be a seednode. 157connect to other nodes they only know by name. In addition, AEMP offers a
158distributed "group database", which maps group names to a list of strings
159- for example, to register worker ports.
160
161A network needs at least one global node to work, and allows every node to
162be a global node.
163
164Any node that loads the L<AnyEvent::MP::Global> module becomes a global
165node and tries to keep connections to all other nodes. So while it can
166make sense to make every node "global" in small networks, it usually makes
167sense to only make seed nodes into global nodes in large networks (nodes
168keep connections to seed nodes and global nodes, so makign them the same
169reduces overhead).
119 170
120=back 171=back
121 172
122=head1 VARIABLES/FUNCTIONS 173=head1 VARIABLES/FUNCTIONS
123 174
125 176
126=cut 177=cut
127 178
128package AnyEvent::MP; 179package AnyEvent::MP;
129 180
181use AnyEvent::MP::Config ();
130use AnyEvent::MP::Kernel; 182use AnyEvent::MP::Kernel;
183use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
131 184
132use common::sense; 185use common::sense;
133 186
134use Carp (); 187use Carp ();
135 188
136use AE (); 189use AE ();
190use Guard ();
137 191
138use base "Exporter"; 192use base "Exporter";
139 193
140our $VERSION = $AnyEvent::MP::Kernel::VERSION; 194our $VERSION = $AnyEvent::MP::Config::VERSION;
141 195
142our @EXPORT = qw( 196our @EXPORT = qw(
143 NODE $NODE *SELF node_of after 197 NODE $NODE *SELF node_of after
144 initialise_node 198 configure
145 snd rcv mon mon_guard kil reg psub spawn 199 snd rcv mon mon_guard kil psub peval spawn cal
146 port 200 port
201 db_set db_del db_reg
202 db_mon db_family db_keys db_values
147); 203);
148 204
149our $SELF; 205our $SELF;
150 206
151sub _self_die() { 207sub _self_die() {
156 212
157=item $thisnode = NODE / $NODE 213=item $thisnode = NODE / $NODE
158 214
159The C<NODE> function returns, and the C<$NODE> variable contains, the node 215The C<NODE> function returns, and the C<$NODE> variable contains, the node
160ID of the node running in the current process. This value is initialised by 216ID of the node running in the current process. This value is initialised by
161a call to C<initialise_node>. 217a call to C<configure>.
162 218
163=item $nodeid = node_of $port 219=item $nodeid = node_of $port
164 220
165Extracts and returns the node ID from a port ID or a node ID. 221Extracts and returns the node ID from a port ID or a node ID.
166 222
167=item initialise_node $profile_name 223=item configure $profile, key => value...
224
225=item configure key => value...
168 226
169Before a node can talk to other nodes on the network (i.e. enter 227Before a node can talk to other nodes on the network (i.e. enter
170"distributed mode") it has to initialise itself - the minimum a node needs 228"distributed mode") it has to configure itself - the minimum a node needs
171to know is its own name, and optionally it should know the addresses of 229to know is its own name, and optionally it should know the addresses of
172some other nodes in the network to discover other nodes. 230some other nodes in the network to discover other nodes.
173 231
174This function initialises a node - it must be called exactly once (or 232This function configures a node - it must be called exactly once (or
175never) before calling other AnyEvent::MP functions. 233never) before calling other AnyEvent::MP functions.
176 234
177The first argument is a profile name. If it is C<undef> or missing, then 235The key/value pairs are basically the same ones as documented for the
178the current nodename will be used instead (i.e. F<uname -n>). 236F<aemp> command line utility (sans the set/del prefix), with these additions:
179 237
238=over 4
239
240=item norc => $boolean (default false)
241
242If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
243be consulted - all configuraiton options must be specified in the
244C<configure> call.
245
246=item force => $boolean (default false)
247
248IF true, then the values specified in the C<configure> will take
249precedence over any values configured via the rc file. The default is for
250the rc file to override any options specified in the program.
251
252=item secure => $pass->($nodeid)
253
254In addition to specifying a boolean, you can specify a code reference that
255is called for every remote execution attempt - the execution request is
256granted iff the callback returns a true value.
257
258See F<semp setsecure> for more info.
259
260=back
261
262=over 4
263
264=item step 1, gathering configuration from profiles
265
180The function then looks up the profile in the aemp configuration (see the 266The function first looks up a profile in the aemp configuration (see the
181L<aemp> commandline utility). 267L<aemp> commandline utility). The profile name can be specified via the
268named C<profile> parameter or can simply be the first parameter). If it is
269missing, then the nodename (F<uname -n>) will be used as profile name.
270
271The profile data is then gathered as follows:
272
273First, all remaining key => value pairs (all of which are conveniently
274undocumented at the moment) will be interpreted as configuration
275data. Then they will be overwritten by any values specified in the global
276default configuration (see the F<aemp> utility), then the chain of
277profiles chosen by the profile name (and any C<parent> attributes).
278
279That means that the values specified in the profile have highest priority
280and the values specified directly via C<configure> have lowest priority,
281and can only be used to specify defaults.
182 282
183If the profile specifies a node ID, then this will become the node ID of 283If the profile specifies a node ID, then this will become the node ID of
184this process. If not, then the profile name will be used as node ID. The 284this process. If not, then the profile name will be used as node ID, with
185special node ID of C<anon/> will be replaced by a random node ID. 285a unique randoms tring (C</%u>) appended.
286
287The node ID can contain some C<%> sequences that are expanded: C<%n>
288is expanded to the local nodename, C<%u> is replaced by a random
289strign to make the node unique. For example, the F<aemp> commandline
290utility uses C<aemp/%n/%u> as nodename, which might expand to
291C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
292
293=item step 2, bind listener sockets
186 294
187The next step is to look up the binds in the profile, followed by binding 295The next step is to look up the binds in the profile, followed by binding
188aemp protocol listeners on all binds specified (it is possible and valid 296aemp protocol listeners on all binds specified (it is possible and valid
189to have no binds, meaning that the node cannot be contacted form the 297to have no binds, meaning that the node cannot be contacted form the
190outside. This means the node cannot talk to other nodes that also have no 298outside. This means the node cannot talk to other nodes that also have no
191binds, but it can still talk to all "normal" nodes). 299binds, but it can still talk to all "normal" nodes).
192 300
193If the profile does not specify a binds list, then the node ID will be 301If the profile does not specify a binds list, then a default of C<*> is
194treated as if it were of the form C<host:port>, which will be resolved and 302used, meaning the node will bind on a dynamically-assigned port on every
195used as binds list. 303local IP address it finds.
196 304
305=item step 3, connect to seed nodes
306
197Lastly, the seeds list from the profile is passed to the 307As the last step, the seed ID list from the profile is passed to the
198L<AnyEvent::MP::Global> module, which will then use it to keep 308L<AnyEvent::MP::Global> module, which will then use it to keep
199connectivity with at least on of those seed nodes at any point in time. 309connectivity with at least one node at any point in time.
200 310
201Example: become a distributed node listening on the guessed noderef, or 311=back
202the one specified via C<aemp> for the current node. This should be the 312
313Example: become a distributed node using the local node name as profile.
203most common form of invocation for "daemon"-type nodes. 314This should be the most common form of invocation for "daemon"-type nodes.
204 315
205 initialise_node; 316 configure
206 317
207Example: become an anonymous node. This form is often used for commandline 318Example: become a semi-anonymous node. This form is often used for
208clients. 319commandline clients.
209 320
210 initialise_node "anon/"; 321 configure nodeid => "myscript/%n/%u";
211 322
212Example: become a distributed node. If there is no profile of the given 323Example: configure a node using a profile called seed, which is suitable
213name, or no binds list was specified, resolve C<localhost:4044> and bind 324for a seed node as it binds on all local addresses on a fixed port (4040,
214on the resulting addresses. 325customary for aemp).
215 326
216 initialise_node "localhost:4044"; 327 # use the aemp commandline utility
328 # aemp profile seed binds '*:4040'
329
330 # then use it
331 configure profile => "seed";
332
333 # or simply use aemp from the shell again:
334 # aemp run profile seed
335
336 # or provide a nicer-to-remember nodeid
337 # aemp run profile seed nodeid "$(hostname)"
217 338
218=item $SELF 339=item $SELF
219 340
220Contains the current port id while executing C<rcv> callbacks or C<psub> 341Contains the current port id while executing C<rcv> callbacks or C<psub>
221blocks. 342blocks.
282sub _kilme { 403sub _kilme {
283 die "received message on port without callback"; 404 die "received message on port without callback";
284} 405}
285 406
286sub port(;&) { 407sub port(;&) {
287 my $id = "$UNIQ." . $ID++; 408 my $id = $UNIQ . ++$ID;
288 my $port = "$NODE#$id"; 409 my $port = "$NODE#$id";
289 410
290 rcv $port, shift || \&_kilme; 411 rcv $port, shift || \&_kilme;
291 412
292 $port 413 $port
331 msg1 => sub { ... }, 452 msg1 => sub { ... },
332 ... 453 ...
333 ; 454 ;
334 455
335Example: temporarily register a rcv callback for a tag matching some port 456Example: temporarily register a rcv callback for a tag matching some port
336(e.g. for a rpc reply) and unregister it after a message was received. 457(e.g. for an rpc reply) and unregister it after a message was received.
337 458
338 rcv $port, $otherport => sub { 459 rcv $port, $otherport => sub {
339 my @reply = @_; 460 my @reply = @_;
340 461
341 rcv $SELF, $otherport; 462 rcv $SELF, $otherport;
343 464
344=cut 465=cut
345 466
346sub rcv($@) { 467sub rcv($@) {
347 my $port = shift; 468 my $port = shift;
348 my ($noderef, $portid) = split /#/, $port, 2; 469 my ($nodeid, $portid) = split /#/, $port, 2;
349 470
350 $NODE{$noderef} == $NODE{""} 471 $NODE{$nodeid} == $NODE{""}
351 or Carp::croak "$port: rcv can only be called on local ports, caught"; 472 or Carp::croak "$port: rcv can only be called on local ports, caught";
352 473
353 while (@_) { 474 while (@_) {
354 if (ref $_[0]) { 475 if (ref $_[0]) {
355 if (my $self = $PORT_DATA{$portid}) { 476 if (my $self = $PORT_DATA{$portid}) {
356 "AnyEvent::MP::Port" eq ref $self 477 "AnyEvent::MP::Port" eq ref $self
357 or Carp::croak "$port: rcv can only be called on message matching ports, caught"; 478 or Carp::croak "$port: rcv can only be called on message matching ports, caught";
358 479
359 $self->[2] = shift; 480 $self->[0] = shift;
360 } else { 481 } else {
361 my $cb = shift; 482 my $cb = shift;
362 $PORT{$portid} = sub { 483 $PORT{$portid} = sub {
363 local $SELF = $port; 484 local $SELF = $port;
364 eval { &$cb }; _self_die if $@; 485 eval { &$cb }; _self_die if $@;
365 }; 486 };
366 } 487 }
367 } elsif (defined $_[0]) { 488 } elsif (defined $_[0]) {
368 my $self = $PORT_DATA{$portid} ||= do { 489 my $self = $PORT_DATA{$portid} ||= do {
369 my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port"; 490 my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
370 491
371 $PORT{$portid} = sub { 492 $PORT{$portid} = sub {
372 local $SELF = $port; 493 local $SELF = $port;
373 494
374 if (my $cb = $self->[1]{$_[0]}) { 495 if (my $cb = $self->[1]{$_[0]}) {
396 } 517 }
397 518
398 $port 519 $port
399} 520}
400 521
522=item peval $port, $coderef[, @args]
523
524Evaluates the given C<$codref> within the contetx of C<$port>, that is,
525when the code throews an exception the C<$port> will be killed.
526
527Any remaining args will be passed to the callback. Any return values will
528be returned to the caller.
529
530This is useful when you temporarily want to execute code in the context of
531a port.
532
533Example: create a port and run some initialisation code in it's context.
534
535 my $port = port { ... };
536
537 peval $port, sub {
538 init
539 or die "unable to init";
540 };
541
542=cut
543
544sub peval($$) {
545 local $SELF = shift;
546 my $cb = shift;
547
548 if (wantarray) {
549 my @res = eval { &$cb };
550 _self_die if $@;
551 @res
552 } else {
553 my $res = eval { &$cb };
554 _self_die if $@;
555 $res
556 }
557}
558
401=item $closure = psub { BLOCK } 559=item $closure = psub { BLOCK }
402 560
403Remembers C<$SELF> and creates a closure out of the BLOCK. When the 561Remembers C<$SELF> and creates a closure out of the BLOCK. When the
404closure is executed, sets up the environment in the same way as in C<rcv> 562closure is executed, sets up the environment in the same way as in C<rcv>
405callbacks, i.e. runtime errors will cause the port to get C<kil>ed. 563callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
564
565The effect is basically as if it returned C<< sub { peval $SELF, sub {
566BLOCK }, @_ } >>.
406 567
407This is useful when you register callbacks from C<rcv> callbacks: 568This is useful when you register callbacks from C<rcv> callbacks:
408 569
409 rcv delayed_reply => sub { 570 rcv delayed_reply => sub {
410 my ($delay, @reply) = @_; 571 my ($delay, @reply) = @_;
446 607
447Monitor the given port and do something when the port is killed or 608Monitor the given port and do something when the port is killed or
448messages to it were lost, and optionally return a guard that can be used 609messages to it were lost, and optionally return a guard that can be used
449to stop monitoring again. 610to stop monitoring again.
450 611
612In the first form (callback), the callback is simply called with any
613number of C<@reason> elements (no @reason means that the port was deleted
614"normally"). Note also that I<< the callback B<must> never die >>, so use
615C<eval> if unsure.
616
617In the second form (another port given), the other port (C<$rcvport>)
618will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
619"normal" kils nothing happens, while under all other conditions, the other
620port is killed with the same reason.
621
622The third form (kill self) is the same as the second form, except that
623C<$rvport> defaults to C<$SELF>.
624
625In the last form (message), a message of the form C<@msg, @reason> will be
626C<snd>.
627
628Monitoring-actions are one-shot: once messages are lost (and a monitoring
629alert was raised), they are removed and will not trigger again.
630
631As a rule of thumb, monitoring requests should always monitor a port from
632a local port (or callback). The reason is that kill messages might get
633lost, just like any other message. Another less obvious reason is that
634even monitoring requests can get lost (for example, when the connection
635to the other node goes down permanently). When monitoring a port locally
636these problems do not exist.
637
451C<mon> effectively guarantees that, in the absence of hardware failures, 638C<mon> effectively guarantees that, in the absence of hardware failures,
452after starting the monitor, either all messages sent to the port will 639after starting the monitor, either all messages sent to the port will
453arrive, or the monitoring action will be invoked after possible message 640arrive, or the monitoring action will be invoked after possible message
454loss has been detected. No messages will be lost "in between" (after 641loss has been detected. No messages will be lost "in between" (after
455the first lost message no further messages will be received by the 642the first lost message no further messages will be received by the
456port). After the monitoring action was invoked, further messages might get 643port). After the monitoring action was invoked, further messages might get
457delivered again. 644delivered again.
458 645
459Note that monitoring-actions are one-shot: once messages are lost (and a 646Inter-host-connection timeouts and monitoring depend on the transport
460monitoring alert was raised), they are removed and will not trigger again. 647used. The only transport currently implemented is TCP, and AnyEvent::MP
648relies on TCP to detect node-downs (this can take 10-15 minutes on a
649non-idle connection, and usually around two hours for idle connections).
461 650
462In the first form (callback), the callback is simply called with any 651This means that monitoring is good for program errors and cleaning up
463number of C<@reason> elements (no @reason means that the port was deleted 652stuff eventually, but they are no replacement for a timeout when you need
464"normally"). Note also that I<< the callback B<must> never die >>, so use 653to ensure some maximum latency.
465C<eval> if unsure.
466
467In the second form (another port given), the other port (C<$rcvport>)
468will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
469"normal" kils nothing happens, while under all other conditions, the other
470port is killed with the same reason.
471
472The third form (kill self) is the same as the second form, except that
473C<$rvport> defaults to C<$SELF>.
474
475In the last form (message), a message of the form C<@msg, @reason> will be
476C<snd>.
477
478As a rule of thumb, monitoring requests should always monitor a port from
479a local port (or callback). The reason is that kill messages might get
480lost, just like any other message. Another less obvious reason is that
481even monitoring requests can get lost (for exmaple, when the connection
482to the other node goes down permanently). When monitoring a port locally
483these problems do not exist.
484 654
485Example: call a given callback when C<$port> is killed. 655Example: call a given callback when C<$port> is killed.
486 656
487 mon $port, sub { warn "port died because of <@_>\n" }; 657 mon $port, sub { warn "port died because of <@_>\n" };
488 658
495 mon $port, $self => "restart"; 665 mon $port, $self => "restart";
496 666
497=cut 667=cut
498 668
499sub mon { 669sub mon {
500 my ($noderef, $port) = split /#/, shift, 2; 670 my ($nodeid, $port) = split /#/, shift, 2;
501 671
502 my $node = $NODE{$noderef} || add_node $noderef; 672 my $node = $NODE{$nodeid} || add_node $nodeid;
503 673
504 my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; 674 my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
505 675
506 unless (ref $cb) { 676 unless (ref $cb) {
507 if (@_) { 677 if (@_) {
516 } 686 }
517 687
518 $node->monitor ($port, $cb); 688 $node->monitor ($port, $cb);
519 689
520 defined wantarray 690 defined wantarray
521 and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) } 691 and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
522} 692}
523 693
524=item $guard = mon_guard $port, $ref, $ref... 694=item $guard = mon_guard $port, $ref, $ref...
525 695
526Monitors the given C<$port> and keeps the passed references. When the port 696Monitors the given C<$port> and keeps the passed references. When the port
549 719
550=item kil $port[, @reason] 720=item kil $port[, @reason]
551 721
552Kill the specified port with the given C<@reason>. 722Kill the specified port with the given C<@reason>.
553 723
554If no C<@reason> is specified, then the port is killed "normally" (ports 724If no C<@reason> is specified, then the port is killed "normally" -
555monitoring other ports will not necessarily die because a port dies 725monitor callback will be invoked, but the kil will not cause linked ports
556"normally"). 726(C<mon $mport, $lport> form) to get killed.
557 727
558Otherwise, linked ports get killed with the same reason (second form of 728If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
559C<mon>, see above). 729form) get killed with the same reason.
560 730
561Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks 731Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
562will be reported as reason C<< die => $@ >>. 732will be reported as reason C<< die => $@ >>.
563 733
564Transport/communication errors are reported as C<< transport_error => 734Transport/communication errors are reported as C<< transport_error =>
583the package, then the package above the package and so on (e.g. 753the package, then the package above the package and so on (e.g.
584C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function 754C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
585exists or it runs out of package names. 755exists or it runs out of package names.
586 756
587The init function is then called with the newly-created port as context 757The init function is then called with the newly-created port as context
588object (C<$SELF>) and the C<@initdata> values as arguments. 758object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
759call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
760the port might not get created.
589 761
590A common idiom is to pass a local port, immediately monitor the spawned 762A common idiom is to pass a local port, immediately monitor the spawned
591port, and in the remote init function, immediately monitor the passed 763port, and in the remote init function, immediately monitor the passed
592local port. This two-way monitoring ensures that both ports get cleaned up 764local port. This two-way monitoring ensures that both ports get cleaned up
593when there is a problem. 765when there is a problem.
594 766
767C<spawn> guarantees that the C<$initfunc> has no visible effects on the
768caller before C<spawn> returns (by delaying invocation when spawn is
769called for the local node).
770
595Example: spawn a chat server port on C<$othernode>. 771Example: spawn a chat server port on C<$othernode>.
596 772
597 # this node, executed from within a port context: 773 # this node, executed from within a port context:
598 my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; 774 my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
599 mon $server; 775 mon $server;
613 789
614sub _spawn { 790sub _spawn {
615 my $port = shift; 791 my $port = shift;
616 my $init = shift; 792 my $init = shift;
617 793
794 # rcv will create the actual port
618 local $SELF = "$NODE#$port"; 795 local $SELF = "$NODE#$port";
619 eval { 796 eval {
620 &{ load_func $init } 797 &{ load_func $init }
621 }; 798 };
622 _self_die if $@; 799 _self_die if $@;
623} 800}
624 801
625sub spawn(@) { 802sub spawn(@) {
626 my ($noderef, undef) = split /#/, shift, 2; 803 my ($nodeid, undef) = split /#/, shift, 2;
627 804
628 my $id = "$RUNIQ." . $ID++; 805 my $id = $RUNIQ . ++$ID;
629 806
630 $_[0] =~ /::/ 807 $_[0] =~ /::/
631 or Carp::croak "spawn init function must be a fully-qualified name, caught"; 808 or Carp::croak "spawn init function must be a fully-qualified name, caught";
632 809
633 snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_; 810 snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
634 811
635 "$noderef#$id" 812 "$nodeid#$id"
636} 813}
814
637 815
638=item after $timeout, @msg 816=item after $timeout, @msg
639 817
640=item after $timeout, $callback 818=item after $timeout, $callback
641 819
657 ? $action[0]() 835 ? $action[0]()
658 : snd @action; 836 : snd @action;
659 }; 837 };
660} 838}
661 839
840=item cal $port, @msg, $callback[, $timeout]
841
842A simple form of RPC - sends a message to the given C<$port> with the
843given contents (C<@msg>), but adds a reply port to the message.
844
845The reply port is created temporarily just for the purpose of receiving
846the reply, and will be C<kil>ed when no longer needed.
847
848A reply message sent to the port is passed to the C<$callback> as-is.
849
850If an optional time-out (in seconds) is given and it is not C<undef>,
851then the callback will be called without any arguments after the time-out
852elapsed and the port is C<kil>ed.
853
854If no time-out is given (or it is C<undef>), then the local port will
855monitor the remote port instead, so it eventually gets cleaned-up.
856
857Currently this function returns the temporary port, but this "feature"
858might go in future versions unless you can make a convincing case that
859this is indeed useful for something.
860
861=cut
862
863sub cal(@) {
864 my $timeout = ref $_[-1] ? undef : pop;
865 my $cb = pop;
866
867 my $port = port {
868 undef $timeout;
869 kil $SELF;
870 &$cb;
871 };
872
873 if (defined $timeout) {
874 $timeout = AE::timer $timeout, 0, sub {
875 undef $timeout;
876 kil $port;
877 $cb->();
878 };
879 } else {
880 mon $_[0], sub {
881 kil $port;
882 $cb->();
883 };
884 }
885
886 push @_, $port;
887 &snd;
888
889 $port
890}
891
892=back
893
894=head1 DISTRIBUTED DATABASE
895
896AnyEvent::MP comes with a simple distributed database. The database will
897be mirrored asynchronously at all global nodes. Other nodes bind to one of
898the global nodes for their needs.
899
900The database consists of a two-level hash - a hash contains a hash which
901contains values.
902
903The top level hash key is called "family", and the second-level hash key
904is called "subkey" or simply "key".
905
906The family must be alphanumeric, i.e. start with a letter and consist
907of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
908pretty much like Perl module names.
909
910As the family namespace is global, it is recommended to prefix family names
911with the name of the application or module using it.
912
913The subkeys must be non-empty strings, with no further restrictions.
914
915The values should preferably be strings, but other perl scalars should
916work as well (such as undef, arrays and hashes).
917
918Every database entry is owned by one node - adding the same family/subkey
919combination on multiple nodes will not cause discomfort for AnyEvent::MP,
920but the result might be nondeterministic, i.e. the key might have
921different values on different nodes.
922
923Different subkeys in the same family can be owned by different nodes
924without problems, and in fact, this is the common method to create worker
925pools. For example, a worker port for image scaling might do this:
926
927 db_set my_image_scalers => $port;
928
929And clients looking for an image scaler will want to get the
930C<my_image_scalers> keys:
931
932 db_keys "my_image_scalers" => 60 => sub {
933 #d##TODO#
934
935=over
936
937=item db_set $family => $subkey [=> $value]
938
939Sets (or replaces) a key to the database - if C<$value> is omitted,
940C<undef> is used instead.
941
942=item db_del $family => $subkey
943
944Deletes a key from the database.
945
946=item $guard = db_reg $family => $subkey [=> $value]
947
948Sets the key on the database and returns a guard. When the guard is
949destroyed, the key is deleted from the database. If C<$value> is missing,
950then C<undef> is used.
951
952=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
953
954Creates a monitor on the given database family. Each time a key is set or
955or is deleted the callback is called with a hash containing the database
956family and an arrayref with subkeys that have changed.
957
958Specifically, if one of the passed subkeys exists in the $familyhash, then
959it is currently set to the value in the $familyhash. Otherwise, it has
960been deleted.
961
962The first call will be with the current contents of the family and all
963keys, as if they were just added.
964
965It is possible that the callback is called with a change event even though
966the subkey is already present and the value has not changed.
967
968The monitoring stops when the guard object is destroyed.
969
970Example: on every change to the family "mygroup", print out all keys.
971
972 my $guard = db_mon mygroup => sub {
973 my ($family, $keys) = @_;
974 print "mygroup members: ", (join " ", keys %$family), "\n";
975 };
976
977Exmaple: wait until the family "My::Module::workers" is non-empty.
978
979 my $guard; $guard = db_mon My::Module::workers => sub {
980 my ($family, $keys) = @_;
981 return unless %$family;
982 undef $guard;
983 print "My::Module::workers now nonempty\n";
984 };
985
986Example: print all changes to the family "AnyRvent::Fantasy::Module".
987
988 my $guard = db_mon AnyRvent::Fantasy::Module => sub {
989 my ($family, $keys) = @_;
990
991 for (@$keys) {
992 print "$_: ",
993 (exists $family->{$_}
994 ? $family->{$_}
995 : "(deleted)"),
996 "\n";
997 }
998 };
999
1000=cut
1001
662=back 1002=back
663 1003
664=head1 AnyEvent::MP vs. Distributed Erlang 1004=head1 AnyEvent::MP vs. Distributed Erlang
665 1005
666AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node 1006AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
667== aemp node, Erlang process == aemp port), so many of the documents and 1007== aemp node, Erlang process == aemp port), so many of the documents and
668programming techniques employed by Erlang apply to AnyEvent::MP. Here is a 1008programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
669sample: 1009sample:
670 1010
671 http://www.Erlang.se/doc/programming_rules.shtml 1011 http://www.erlang.se/doc/programming_rules.shtml
672 http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4 1012 http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
673 http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6 1013 http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
674 http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5 1014 http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
675 1015
676Despite the similarities, there are also some important differences: 1016Despite the similarities, there are also some important differences:
677 1017
678=over 4 1018=over 4
679 1019
680=item * Node IDs are arbitrary strings in AEMP. 1020=item * Node IDs are arbitrary strings in AEMP.
681 1021
682Erlang relies on special naming and DNS to work everywhere in the same 1022Erlang relies on special naming and DNS to work everywhere in the same
683way. AEMP relies on each node somehow knowing its own address(es) (e.g. by 1023way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
684configuraiton or DNS), but will otherwise discover other odes itself. 1024configuration or DNS), and possibly the addresses of some seed nodes, but
1025will otherwise discover other nodes (and their IDs) itself.
685 1026
686=item * Erlang has a "remote ports are like local ports" philosophy, AEMP 1027=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
687uses "local ports are like remote ports". 1028uses "local ports are like remote ports".
688 1029
689The failure modes for local ports are quite different (runtime errors 1030The failure modes for local ports are quite different (runtime errors
698ports being the special case/exception, where transport errors cannot 1039ports being the special case/exception, where transport errors cannot
699occur. 1040occur.
700 1041
701=item * Erlang uses processes and a mailbox, AEMP does not queue. 1042=item * Erlang uses processes and a mailbox, AEMP does not queue.
702 1043
703Erlang uses processes that selectively receive messages, and therefore 1044Erlang uses processes that selectively receive messages out of order, and
704needs a queue. AEMP is event based, queuing messages would serve no 1045therefore needs a queue. AEMP is event based, queuing messages would serve
705useful purpose. For the same reason the pattern-matching abilities of 1046no useful purpose. For the same reason the pattern-matching abilities
706AnyEvent::MP are more limited, as there is little need to be able to 1047of AnyEvent::MP are more limited, as there is little need to be able to
707filter messages without dequeing them. 1048filter messages without dequeuing them.
708 1049
709(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP). 1050This is not a philosophical difference, but simply stems from AnyEvent::MP
1051being event-based, while Erlang is process-based.
1052
1053You cna have a look at L<Coro::MP> for a more Erlang-like process model on
1054top of AEMP and Coro threads.
710 1055
711=item * Erlang sends are synchronous, AEMP sends are asynchronous. 1056=item * Erlang sends are synchronous, AEMP sends are asynchronous.
712 1057
713Sending messages in Erlang is synchronous and blocks the process (and 1058Sending messages in Erlang is synchronous and blocks the process until
1059a conenction has been established and the message sent (and so does not
714so does not need a queue that can overflow). AEMP sends are immediate, 1060need a queue that can overflow). AEMP sends return immediately, connection
715connection establishment is handled in the background. 1061establishment is handled in the background.
716 1062
717=item * Erlang suffers from silent message loss, AEMP does not. 1063=item * Erlang suffers from silent message loss, AEMP does not.
718 1064
719Erlang makes few guarantees on messages delivery - messages can get lost 1065Erlang implements few guarantees on messages delivery - messages can get
720without any of the processes realising it (i.e. you send messages a, b, 1066lost without any of the processes realising it (i.e. you send messages a,
721and c, and the other side only receives messages a and c). 1067b, and c, and the other side only receives messages a and c).
722 1068
723AEMP guarantees correct ordering, and the guarantee that after one message 1069AEMP guarantees (modulo hardware errors) correct ordering, and the
724is lost, all following ones sent to the same port are lost as well, until 1070guarantee that after one message is lost, all following ones sent to the
725monitoring raises an error, so there are no silent "holes" in the message 1071same port are lost as well, until monitoring raises an error, so there are
726sequence. 1072no silent "holes" in the message sequence.
1073
1074If you want your software to be very reliable, you have to cope with
1075corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
1076simply tries to work better in common error cases, such as when a network
1077link goes down.
727 1078
728=item * Erlang can send messages to the wrong port, AEMP does not. 1079=item * Erlang can send messages to the wrong port, AEMP does not.
729 1080
730In Erlang it is quite likely that a node that restarts reuses a process ID 1081In Erlang it is quite likely that a node that restarts reuses an Erlang
731known to other nodes for a completely different process, causing messages 1082process ID known to other nodes for a completely different process,
732destined for that process to end up in an unrelated process. 1083causing messages destined for that process to end up in an unrelated
1084process.
733 1085
734AEMP never reuses port IDs, so old messages or old port IDs floating 1086AEMP does not reuse port IDs, so old messages or old port IDs floating
735around in the network will not be sent to an unrelated port. 1087around in the network will not be sent to an unrelated port.
736 1088
737=item * Erlang uses unprotected connections, AEMP uses secure 1089=item * Erlang uses unprotected connections, AEMP uses secure
738authentication and can use TLS. 1090authentication and can use TLS.
739 1091
742 1094
743=item * The AEMP protocol is optimised for both text-based and binary 1095=item * The AEMP protocol is optimised for both text-based and binary
744communications. 1096communications.
745 1097
746The AEMP protocol, unlike the Erlang protocol, supports both programming 1098The AEMP protocol, unlike the Erlang protocol, supports both programming
747language independent text-only protocols (good for debugging) and binary, 1099language independent text-only protocols (good for debugging), and binary,
748language-specific serialisers (e.g. Storable). By default, unless TLS is 1100language-specific serialisers (e.g. Storable). By default, unless TLS is
749used, the protocol is actually completely text-based. 1101used, the protocol is actually completely text-based.
750 1102
751It has also been carefully designed to be implementable in other languages 1103It has also been carefully designed to be implementable in other languages
752with a minimum of work while gracefully degrading functionality to make the 1104with a minimum of work while gracefully degrading functionality to make the
753protocol simple. 1105protocol simple.
754 1106
755=item * AEMP has more flexible monitoring options than Erlang. 1107=item * AEMP has more flexible monitoring options than Erlang.
756 1108
757In Erlang, you can chose to receive I<all> exit signals as messages 1109In Erlang, you can chose to receive I<all> exit signals as messages or
758or I<none>, there is no in-between, so monitoring single processes is 1110I<none>, there is no in-between, so monitoring single Erlang processes is
759difficult to implement. Monitoring in AEMP is more flexible than in 1111difficult to implement.
760Erlang, as one can choose between automatic kill, exit message or callback 1112
761on a per-process basis. 1113Monitoring in AEMP is more flexible than in Erlang, as one can choose
1114between automatic kill, exit message or callback on a per-port basis.
762 1115
763=item * Erlang tries to hide remote/local connections, AEMP does not. 1116=item * Erlang tries to hide remote/local connections, AEMP does not.
764 1117
765Monitoring in Erlang is not an indicator of process death/crashes, in the 1118Monitoring in Erlang is not an indicator of process death/crashes, in the
766same way as linking is (except linking is unreliable in Erlang). 1119same way as linking is (except linking is unreliable in Erlang).
788overhead, as well as having to keep a proxy object everywhere. 1141overhead, as well as having to keep a proxy object everywhere.
789 1142
790Strings can easily be printed, easily serialised etc. and need no special 1143Strings can easily be printed, easily serialised etc. and need no special
791procedures to be "valid". 1144procedures to be "valid".
792 1145
793And as a result, a miniport consists of a single closure stored in a 1146And as a result, a port with just a default receiver consists of a single
794global hash - it can't become much cheaper. 1147code reference stored in a global hash - it can't become much cheaper.
795 1148
796=item Why favour JSON, why not a real serialising format such as Storable? 1149=item Why favour JSON, why not a real serialising format such as Storable?
797 1150
798In fact, any AnyEvent::MP node will happily accept Storable as framing 1151In fact, any AnyEvent::MP node will happily accept Storable as framing
799format, but currently there is no way to make a node use Storable by 1152format, but currently there is no way to make a node use Storable by
815 1168
816L<AnyEvent::MP::Intro> - a gentle introduction. 1169L<AnyEvent::MP::Intro> - a gentle introduction.
817 1170
818L<AnyEvent::MP::Kernel> - more, lower-level, stuff. 1171L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
819 1172
820L<AnyEvent::MP::Global> - network maintainance and port groups, to find 1173L<AnyEvent::MP::Global> - network maintenance and port groups, to find
821your applications. 1174your applications.
1175
1176L<AnyEvent::MP::DataConn> - establish data connections between nodes.
1177
1178L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
1179all nodes.
822 1180
823L<AnyEvent>. 1181L<AnyEvent>.
824 1182
825=head1 AUTHOR 1183=head1 AUTHOR
826 1184

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