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Revision 1.108 by root, Wed Dec 30 13:37:53 2009 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 prot 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 - WIP
46 AnyEvent::MP::Transport - mostly stable 57 AnyEvent::MP::Kernel - mostly stable API.
47 58 AnyEvent::MP::Global - stable API.
48 stay tuned.
49 59
50=head1 DESCRIPTION 60=head1 DESCRIPTION
51 61
52This module (-family) implements a simple message passing framework. 62This module (-family) implements a simple message passing framework.
53 63
54Despite its simplicity, you can securely message other processes running 64Despite its simplicity, you can securely message other processes running
55on the same or other hosts. 65on the same or other hosts, and you can supervise entities remotely.
56 66
57For 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>
58manual page. 68manual page and the examples under F<eg/>.
59
60At the moment, this module family is severly broken and underdocumented,
61so do not use. This was uploaded mainly to reserve the CPAN namespace -
62stay tuned!
63 69
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 will not be queued. 80some messages. Messages send to ports will not be queued, regardless of
81anything was listening for them or not.
74 82
75=item port ID - C<noderef#portname> 83=item port ID - C<nodeid#portname>
76 84
77A port ID is the concatenation of a noderef, a hash-mark (C<#>) as 85A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
78separator, and a port name (a printable string of unspecified format). An 86separator, and a port name (a printable string of unspecified format).
79exception is the the node port, whose ID is identical to its node
80reference.
81 87
82=item node 88=item node
83 89
84A node is a single process containing at least one port - the node port, 90A node is a single process containing at least one port - the node port,
85which provides nodes to manage each other remotely, and to create new 91which enables nodes to manage each other remotely, and to create new
86ports. 92ports.
87 93
88Nodes are either private (single-process only), slaves (can only talk to 94Nodes are either public (have one or more listening ports) or private
89public nodes, but do not need an open port) or public nodes (connectable 95(no listening ports). Private nodes cannot talk to other private nodes
90from any other node). 96currently.
91 97
92=item node ID - C<[a-za-Z0-9_\-.:]+> 98=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>
93 99
94A node ID is a string that either simply identifies the node (for 100A node ID is a string that uniquely identifies the node within a
95private and slave nodes), or contains a recipe on how to reach a given 101network. Depending on the configuration used, node IDs can look like a
96node (for public nodes). 102hostname, a hostname and a port, or a random string. AnyEvent::MP itself
103doesn't interpret node IDs in any way.
97 104
98This recipe is simply a comma-separated list of C<address:port> pairs (for 105=item binds - C<ip:port>
99TCP/IP, other protocols might look different).
100 106
101Node references come in two flavours: resolved (containing only numerical 107Nodes can only talk to each other by creating some kind of connection to
102addresses) or unresolved (where hostnames are used instead of addresses). 108each other. To do this, nodes should listen on one or more local transport
109endpoints - binds. Currently, only standard C<ip:port> specifications can
110be used, which specify TCP ports to listen on.
103 111
104Before using an unresolved node reference in a message you first have to 112=item seed nodes
105resolve it. 113
114When a node starts, it knows nothing about the network. To teach the node
115about the network it first has to contact some other node within the
116network. This node is called a seed.
117
118Apart from the fact that other nodes know them as seed nodes and they have
119to have fixed listening addresses, seed nodes are perfectly normal nodes -
120any node can function as a seed node for others.
121
122In addition to discovering the network, seed nodes are also used to
123maintain the network and to connect nodes that otherwise would have
124trouble connecting. They form the backbone of an AnyEvent::MP network.
125
126Seed nodes are expected to be long-running, and at least one seed node
127should always be available. They should also be relatively responsive - a
128seed node that blocks for long periods will slow down everybody else.
129
130=item seeds - C<host:port>
131
132Seeds are transport endpoint(s) (usually a hostname/IP address and a
133TCP port) of nodes that should be used as seed nodes.
134
135The nodes listening on those endpoints are expected to be long-running,
136and at least one of those should always be available. When nodes run out
137of connections (e.g. due to a network error), they try to re-establish
138connections to some seednodes again to join the network.
106 139
107=back 140=back
108 141
109=head1 VARIABLES/FUNCTIONS 142=head1 VARIABLES/FUNCTIONS
110 143
122 155
123use AE (); 156use AE ();
124 157
125use base "Exporter"; 158use base "Exporter";
126 159
127our $VERSION = $AnyEvent::MP::Kernel::VERSION; 160our $VERSION = 1.24;
128 161
129our @EXPORT = qw( 162our @EXPORT = qw(
130 NODE $NODE *SELF node_of after 163 NODE $NODE *SELF node_of after
131 resolve_node initialise_node 164 configure
132 snd rcv mon mon_guard kil reg psub spawn 165 snd rcv mon mon_guard kil psub peval spawn cal
133 port 166 port
134); 167);
135 168
136our $SELF; 169our $SELF;
137 170
141 kil $SELF, die => $msg; 174 kil $SELF, die => $msg;
142} 175}
143 176
144=item $thisnode = NODE / $NODE 177=item $thisnode = NODE / $NODE
145 178
146The C<NODE> function returns, and the C<$NODE> variable contains the 179The C<NODE> function returns, and the C<$NODE> variable contains, the node
147node id of the local node. The value is initialised by a call to 180ID of the node running in the current process. This value is initialised by
148C<initialise_node>. 181a call to C<configure>.
149 182
150=item $nodeid = node_of $port 183=item $nodeid = node_of $port
151 184
152Extracts and returns the noderef from a port ID or a node ID. 185Extracts and returns the node ID from a port ID or a node ID.
153 186
154=item initialise_node $profile_name 187=item configure $profile, key => value...
155 188
189=item configure key => value...
190
156Before a node can talk to other nodes on the network it has to initialise 191Before a node can talk to other nodes on the network (i.e. enter
157itself - the minimum a node needs to know is it's own name, and optionally 192"distributed mode") it has to configure itself - the minimum a node needs
158it should know the noderefs of some other nodes in the network. 193to know is its own name, and optionally it should know the addresses of
194some other nodes in the network to discover other nodes.
159 195
196The key/value pairs are basically the same ones as documented for the
197F<aemp> command line utility (sans the set/del prefix).
198
160This function initialises a node - it must be called exactly once (or 199This function configures a node - it must be called exactly once (or
161never) before calling other AnyEvent::MP functions. 200never) before calling other AnyEvent::MP functions.
162 201
163All arguments (optionally except for the first) are noderefs, which can be
164either resolved or unresolved.
165
166The first argument will be looked up in the configuration database first
167(if it is C<undef> then the current nodename will be used instead) to find
168the relevant configuration profile (see L<aemp>). If none is found then
169the default configuration is used. The configuration supplies additional
170seed/master nodes and can override the actual noderef.
171
172There are two types of networked nodes, public nodes and slave nodes:
173
174=over 4 202=over 4
175 203
176=item public nodes 204=item step 1, gathering configuration from profiles
177 205
178For public nodes, C<$noderef> (supplied either directly to 206The function first looks up a profile in the aemp configuration (see the
179C<initialise_node> or indirectly via a profile or the nodename) must be a 207L<aemp> commandline utility). The profile name can be specified via the
180noderef (possibly unresolved, in which case it will be resolved). 208named C<profile> parameter or can simply be the first parameter). If it is
209missing, then the nodename (F<uname -n>) will be used as profile name.
181 210
182After resolving, the node will bind itself on all endpoints. 211The profile data is then gathered as follows:
183 212
184=item slave nodes 213First, all remaining key => value pairs (all of which are conveniently
214undocumented at the moment) will be interpreted as configuration
215data. Then they will be overwritten by any values specified in the global
216default configuration (see the F<aemp> utility), then the chain of
217profiles chosen by the profile name (and any C<parent> attributes).
185 218
186When the C<$noderef> (either as given or overriden by the config file) 219That means that the values specified in the profile have highest priority
187is the special string C<slave/>, then the node will become a slave 220and the values specified directly via C<configure> have lowest priority,
188node. Slave nodes cannot be contacted from outside, and cannot talk to 221and can only be used to specify defaults.
189each other (at least in this version of AnyEvent::MP).
190 222
191Slave nodes work by creating connections to all public nodes, using the 223If the profile specifies a node ID, then this will become the node ID of
192L<AnyEvent::MP::Global> service. 224this process. If not, then the profile name will be used as node ID. The
225special node ID of C<anon/> will be replaced by a random node ID.
226
227=item step 2, bind listener sockets
228
229The next step is to look up the binds in the profile, followed by binding
230aemp protocol listeners on all binds specified (it is possible and valid
231to have no binds, meaning that the node cannot be contacted form the
232outside. This means the node cannot talk to other nodes that also have no
233binds, but it can still talk to all "normal" nodes).
234
235If the profile does not specify a binds list, then a default of C<*> is
236used, meaning the node will bind on a dynamically-assigned port on every
237local IP address it finds.
238
239=item step 3, connect to seed nodes
240
241As the last step, the seeds list from the profile is passed to the
242L<AnyEvent::MP::Global> module, which will then use it to keep
243connectivity with at least one node at any point in time.
193 244
194=back 245=back
195 246
196After initialising itself, the node will connect to all additional 247Example: become a distributed node using the local node name as profile.
197C<$seednodes> that are specified diretcly or via a profile. Seednodes are 248This should be the most common form of invocation for "daemon"-type nodes.
198optional and can be used to quickly bootstrap the node into an existing
199network.
200 249
201All the seednodes will also be specially marked to automatically retry 250 configure
202connecting to them indefinitely, so make sure that seednodes are really
203reliable and up (this might also change in the future).
204 251
205Example: become a public node listening on the guessed noderef, or the one 252Example: become an anonymous node. This form is often used for commandline
206specified via C<aemp> for the current node. This should be the most common 253clients.
207form of invocation for "daemon"-type nodes.
208 254
209 initialise_node; 255 configure nodeid => "anon/";
210 256
211Example: become a slave node to any of the the seednodes specified via 257Example: configure a node using a profile called seed, which si suitable
212C<aemp>. This form is often used for commandline clients. 258for a seed node as it binds on all local addresses on a fixed port (4040,
259customary for aemp).
213 260
214 initialise_node "slave/"; 261 # use the aemp commandline utility
262 # aemp profile seed nodeid anon/ binds '*:4040'
215 263
216Example: become a public node, and try to contact some well-known master 264 # then use it
217servers to become part of the network. 265 configure profile => "seed";
218 266
219 initialise_node undef, "master1", "master2"; 267 # or simply use aemp from the shell again:
268 # aemp run profile seed
220 269
221Example: become a public node listening on port C<4041>. 270 # or provide a nicer-to-remember nodeid
222 271 # aemp run profile seed nodeid "$(hostname)"
223 initialise_node 4041;
224
225Example: become a public node, only visible on localhost port 4044.
226
227 initialise_node "localhost:4044";
228
229=item $cv = resolve_node $noderef
230
231Takes an unresolved node reference that may contain hostnames and
232abbreviated IDs, resolves all of them and returns a resolved node
233reference.
234
235In addition to C<address:port> pairs allowed in resolved noderefs, the
236following forms are supported:
237
238=over 4
239
240=item the empty string
241
242An empty-string component gets resolved as if the default port (4040) was
243specified.
244
245=item naked port numbers (e.g. C<1234>)
246
247These are resolved by prepending the local nodename and a colon, to be
248further resolved.
249
250=item hostnames (e.g. C<localhost:1234>, C<localhost>)
251
252These are resolved by using AnyEvent::DNS to resolve them, optionally
253looking up SRV records for the C<aemp=4040> port, if no port was
254specified.
255
256=back
257 272
258=item $SELF 273=item $SELF
259 274
260Contains the current port id while executing C<rcv> callbacks or C<psub> 275Contains the current port id while executing C<rcv> callbacks or C<psub>
261blocks. 276blocks.
262 277
263=item SELF, %SELF, @SELF... 278=item *SELF, SELF, %SELF, @SELF...
264 279
265Due to some quirks in how perl exports variables, it is impossible to 280Due to some quirks in how perl exports variables, it is impossible to
266just export C<$SELF>, all the symbols called C<SELF> are exported by this 281just export C<$SELF>, all the symbols named C<SELF> are exported by this
267module, but only C<$SELF> is currently used. 282module, but only C<$SELF> is currently used.
268 283
269=item snd $port, type => @data 284=item snd $port, type => @data
270 285
271=item snd $port, @msg 286=item snd $port, @msg
272 287
273Send the given message to the given port ID, which can identify either 288Send the given message to the given port, which can identify either a
274a local or a remote port, and must be a port ID. 289local or a remote port, and must be a port ID.
275 290
276While the message can be about anything, it is highly recommended to use a 291While the message can be almost anything, it is highly recommended to
277string as first element (a port ID, or some word that indicates a request 292use a string as first element (a port ID, or some word that indicates a
278type etc.). 293request type etc.) and to consist if only simple perl values (scalars,
294arrays, hashes) - if you think you need to pass an object, think again.
279 295
280The message data effectively becomes read-only after a call to this 296The message data logically becomes read-only after a call to this
281function: modifying any argument is not allowed and can cause many 297function: modifying any argument (or values referenced by them) is
282problems. 298forbidden, as there can be considerable time between the call to C<snd>
299and the time the message is actually being serialised - in fact, it might
300never be copied as within the same process it is simply handed to the
301receiving port.
283 302
284The type of data you can transfer depends on the transport protocol: when 303The type of data you can transfer depends on the transport protocol: when
285JSON is used, then only strings, numbers and arrays and hashes consisting 304JSON is used, then only strings, numbers and arrays and hashes consisting
286of those are allowed (no objects). When Storable is used, then anything 305of those are allowed (no objects). When Storable is used, then anything
287that Storable can serialise and deserialise is allowed, and for the local 306that Storable can serialise and deserialise is allowed, and for the local
288node, anything can be passed. 307node, anything can be passed. Best rely only on the common denominator of
308these.
289 309
290=item $local_port = port 310=item $local_port = port
291 311
292Create a new local port object and returns its port ID. Initially it has 312Create a new local port object and returns its port ID. Initially it has
293no callbacks set and will throw an error when it receives messages. 313no callbacks set and will throw an error when it receives messages.
366 msg1 => sub { ... }, 386 msg1 => sub { ... },
367 ... 387 ...
368 ; 388 ;
369 389
370Example: temporarily register a rcv callback for a tag matching some port 390Example: temporarily register a rcv callback for a tag matching some port
371(e.g. for a rpc reply) and unregister it after a message was received. 391(e.g. for an rpc reply) and unregister it after a message was received.
372 392
373 rcv $port, $otherport => sub { 393 rcv $port, $otherport => sub {
374 my @reply = @_; 394 my @reply = @_;
375 395
376 rcv $SELF, $otherport; 396 rcv $SELF, $otherport;
378 398
379=cut 399=cut
380 400
381sub rcv($@) { 401sub rcv($@) {
382 my $port = shift; 402 my $port = shift;
383 my ($noderef, $portid) = split /#/, $port, 2; 403 my ($nodeid, $portid) = split /#/, $port, 2;
384 404
385 $NODE{$noderef} == $NODE{""} 405 $NODE{$nodeid} == $NODE{""}
386 or Carp::croak "$port: rcv can only be called on local ports, caught"; 406 or Carp::croak "$port: rcv can only be called on local ports, caught";
387 407
388 while (@_) { 408 while (@_) {
389 if (ref $_[0]) { 409 if (ref $_[0]) {
390 if (my $self = $PORT_DATA{$portid}) { 410 if (my $self = $PORT_DATA{$portid}) {
391 "AnyEvent::MP::Port" eq ref $self 411 "AnyEvent::MP::Port" eq ref $self
392 or Carp::croak "$port: rcv can only be called on message matching ports, caught"; 412 or Carp::croak "$port: rcv can only be called on message matching ports, caught";
393 413
394 $self->[2] = shift; 414 $self->[0] = shift;
395 } else { 415 } else {
396 my $cb = shift; 416 my $cb = shift;
397 $PORT{$portid} = sub { 417 $PORT{$portid} = sub {
398 local $SELF = $port; 418 local $SELF = $port;
399 eval { &$cb }; _self_die if $@; 419 eval { &$cb }; _self_die if $@;
400 }; 420 };
401 } 421 }
402 } elsif (defined $_[0]) { 422 } elsif (defined $_[0]) {
403 my $self = $PORT_DATA{$portid} ||= do { 423 my $self = $PORT_DATA{$portid} ||= do {
404 my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port"; 424 my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
405 425
406 $PORT{$portid} = sub { 426 $PORT{$portid} = sub {
407 local $SELF = $port; 427 local $SELF = $port;
408 428
409 if (my $cb = $self->[1]{$_[0]}) { 429 if (my $cb = $self->[1]{$_[0]}) {
431 } 451 }
432 452
433 $port 453 $port
434} 454}
435 455
456=item peval $port, $coderef[, @args]
457
458Evaluates the given C<$codref> within the contetx of C<$port>, that is,
459when the code throews an exception the C<$port> will be killed.
460
461Any remaining args will be passed to the callback. Any return values will
462be returned to the caller.
463
464This is useful when you temporarily want to execute code in the context of
465a port.
466
467Example: create a port and run some initialisation code in it's context.
468
469 my $port = port { ... };
470
471 peval $port, sub {
472 init
473 or die "unable to init";
474 };
475
476=cut
477
478sub peval($$) {
479 local $SELF = shift;
480 my $cb = shift;
481
482 if (wantarray) {
483 my @res = eval { &$cb };
484 _self_die if $@;
485 @res
486 } else {
487 my $res = eval { &$cb };
488 _self_die if $@;
489 $res
490 }
491}
492
436=item $closure = psub { BLOCK } 493=item $closure = psub { BLOCK }
437 494
438Remembers C<$SELF> and creates a closure out of the BLOCK. When the 495Remembers C<$SELF> and creates a closure out of the BLOCK. When the
439closure is executed, sets up the environment in the same way as in C<rcv> 496closure is executed, sets up the environment in the same way as in C<rcv>
440callbacks, i.e. runtime errors will cause the port to get C<kil>ed. 497callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
498
499The effect is basically as if it returned C<< sub { peval $SELF, sub {
500BLOCK } } >>.
441 501
442This is useful when you register callbacks from C<rcv> callbacks: 502This is useful when you register callbacks from C<rcv> callbacks:
443 503
444 rcv delayed_reply => sub { 504 rcv delayed_reply => sub {
445 my ($delay, @reply) = @_; 505 my ($delay, @reply) = @_;
469 $res 529 $res
470 } 530 }
471 } 531 }
472} 532}
473 533
474=item $guard = mon $port, $cb->(@reason) 534=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475 535
476=item $guard = mon $port, $rcvport 536=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477 537
478=item $guard = mon $port 538=item $guard = mon $port # kill $SELF when $port dies
479 539
480=item $guard = mon $port, $rcvport, @msg 540=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481 541
482Monitor the given port and do something when the port is killed or 542Monitor the given port and do something when the port is killed or
483messages to it were lost, and optionally return a guard that can be used 543messages to it were lost, and optionally return a guard that can be used
484to stop monitoring again. 544to stop monitoring again.
485
486C<mon> effectively guarantees that, in the absence of hardware failures,
487that after starting the monitor, either all messages sent to the port
488will arrive, or the monitoring action will be invoked after possible
489message loss has been detected. No messages will be lost "in between"
490(after the first lost message no further messages will be received by the
491port). After the monitoring action was invoked, further messages might get
492delivered again.
493
494Note that monitoring-actions are one-shot: once released, they are removed
495and will not trigger again.
496 545
497In the first form (callback), the callback is simply called with any 546In the first form (callback), the callback is simply called with any
498number of C<@reason> elements (no @reason means that the port was deleted 547number of C<@reason> elements (no @reason means that the port was deleted
499"normally"). Note also that I<< the callback B<must> never die >>, so use 548"normally"). Note also that I<< the callback B<must> never die >>, so use
500C<eval> if unsure. 549C<eval> if unsure.
501 550
502In the second form (another port given), the other port (C<$rcvport>) 551In the second form (another port given), the other port (C<$rcvport>)
503will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on 552will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
504"normal" kils nothing happens, while under all other conditions, the other 553"normal" kils nothing happens, while under all other conditions, the other
505port is killed with the same reason. 554port is killed with the same reason.
506 555
507The third form (kill self) is the same as the second form, except that 556The third form (kill self) is the same as the second form, except that
508C<$rvport> defaults to C<$SELF>. 557C<$rvport> defaults to C<$SELF>.
509 558
510In the last form (message), a message of the form C<@msg, @reason> will be 559In the last form (message), a message of the form C<@msg, @reason> will be
511C<snd>. 560C<snd>.
561
562Monitoring-actions are one-shot: once messages are lost (and a monitoring
563alert was raised), they are removed and will not trigger again.
512 564
513As a rule of thumb, monitoring requests should always monitor a port from 565As a rule of thumb, monitoring requests should always monitor a port from
514a local port (or callback). The reason is that kill messages might get 566a local port (or callback). The reason is that kill messages might get
515lost, just like any other message. Another less obvious reason is that 567lost, just like any other message. Another less obvious reason is that
516even monitoring requests can get lost (for exmaple, when the connection 568even monitoring requests can get lost (for example, when the connection
517to the other node goes down permanently). When monitoring a port locally 569to the other node goes down permanently). When monitoring a port locally
518these problems do not exist. 570these problems do not exist.
519 571
572C<mon> effectively guarantees that, in the absence of hardware failures,
573after starting the monitor, either all messages sent to the port will
574arrive, or the monitoring action will be invoked after possible message
575loss has been detected. No messages will be lost "in between" (after
576the first lost message no further messages will be received by the
577port). After the monitoring action was invoked, further messages might get
578delivered again.
579
580Inter-host-connection timeouts and monitoring depend on the transport
581used. The only transport currently implemented is TCP, and AnyEvent::MP
582relies on TCP to detect node-downs (this can take 10-15 minutes on a
583non-idle connection, and usually around two hours for idle connections).
584
585This means that monitoring is good for program errors and cleaning up
586stuff eventually, but they are no replacement for a timeout when you need
587to ensure some maximum latency.
588
520Example: call a given callback when C<$port> is killed. 589Example: call a given callback when C<$port> is killed.
521 590
522 mon $port, sub { warn "port died because of <@_>\n" }; 591 mon $port, sub { warn "port died because of <@_>\n" };
523 592
524Example: kill ourselves when C<$port> is killed abnormally. 593Example: kill ourselves when C<$port> is killed abnormally.
530 mon $port, $self => "restart"; 599 mon $port, $self => "restart";
531 600
532=cut 601=cut
533 602
534sub mon { 603sub mon {
535 my ($noderef, $port) = split /#/, shift, 2; 604 my ($nodeid, $port) = split /#/, shift, 2;
536 605
537 my $node = $NODE{$noderef} || add_node $noderef; 606 my $node = $NODE{$nodeid} || add_node $nodeid;
538 607
539 my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,'; 608 my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
540 609
541 unless (ref $cb) { 610 unless (ref $cb) {
542 if (@_) { 611 if (@_) {
551 } 620 }
552 621
553 $node->monitor ($port, $cb); 622 $node->monitor ($port, $cb);
554 623
555 defined wantarray 624 defined wantarray
556 and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) } 625 and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
557} 626}
558 627
559=item $guard = mon_guard $port, $ref, $ref... 628=item $guard = mon_guard $port, $ref, $ref...
560 629
561Monitors the given C<$port> and keeps the passed references. When the port 630Monitors the given C<$port> and keeps the passed references. When the port
562is killed, the references will be freed. 631is killed, the references will be freed.
563 632
564Optionally returns a guard that will stop the monitoring. 633Optionally returns a guard that will stop the monitoring.
565 634
566This function is useful when you create e.g. timers or other watchers and 635This function is useful when you create e.g. timers or other watchers and
567want to free them when the port gets killed: 636want to free them when the port gets killed (note the use of C<psub>):
568 637
569 $port->rcv (start => sub { 638 $port->rcv (start => sub {
570 my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { 639 my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571 undef $timer if 0.9 < rand; 640 undef $timer if 0.9 < rand;
572 }); 641 });
573 }); 642 });
574 643
575=cut 644=cut
584 653
585=item kil $port[, @reason] 654=item kil $port[, @reason]
586 655
587Kill the specified port with the given C<@reason>. 656Kill the specified port with the given C<@reason>.
588 657
589If no C<@reason> is specified, then the port is killed "normally" (linked 658If no C<@reason> is specified, then the port is killed "normally" -
590ports will not be kileld, or even notified). 659monitor callback will be invoked, but the kil will not cause linked ports
660(C<mon $mport, $lport> form) to get killed.
591 661
592Otherwise, linked ports get killed with the same reason (second form of 662If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
593C<mon>, see below). 663form) get killed with the same reason.
594 664
595Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks 665Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596will be reported as reason C<< die => $@ >>. 666will be reported as reason C<< die => $@ >>.
597 667
598Transport/communication errors are reported as C<< transport_error => 668Transport/communication errors are reported as C<< transport_error =>
603=item $port = spawn $node, $initfunc[, @initdata] 673=item $port = spawn $node, $initfunc[, @initdata]
604 674
605Creates a port on the node C<$node> (which can also be a port ID, in which 675Creates a port on the node C<$node> (which can also be a port ID, in which
606case it's the node where that port resides). 676case it's the node where that port resides).
607 677
608The port ID of the newly created port is return immediately, and it is 678The port ID of the newly created port is returned immediately, and it is
609permissible to immediately start sending messages or monitor the port. 679possible to immediately start sending messages or to monitor the port.
610 680
611After the port has been created, the init function is 681After the port has been created, the init function is called on the remote
612called. This function must be a fully-qualified function name 682node, in the same context as a C<rcv> callback. This function must be a
613(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main 683fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614program, use C<::name>. 684specify a function in the main program, use C<::name>.
615 685
616If the function doesn't exist, then the node tries to C<require> 686If the function doesn't exist, then the node tries to C<require>
617the package, then the package above the package and so on (e.g. 687the package, then the package above the package and so on (e.g.
618C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function 688C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619exists or it runs out of package names. 689exists or it runs out of package names.
620 690
621The init function is then called with the newly-created port as context 691The init function is then called with the newly-created port as context
622object (C<$SELF>) and the C<@initdata> values as arguments. 692object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
693call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
694the port might not get created.
623 695
624A common idiom is to pass your own port, monitor the spawned port, and 696A common idiom is to pass a local port, immediately monitor the spawned
625in the init function, monitor the original port. This two-way monitoring 697port, and in the remote init function, immediately monitor the passed
626ensures that both ports get cleaned up when there is a problem. 698local port. This two-way monitoring ensures that both ports get cleaned up
699when there is a problem.
700
701C<spawn> guarantees that the C<$initfunc> has no visible effects on the
702caller before C<spawn> returns (by delaying invocation when spawn is
703called for the local node).
627 704
628Example: spawn a chat server port on C<$othernode>. 705Example: spawn a chat server port on C<$othernode>.
629 706
630 # this node, executed from within a port context: 707 # this node, executed from within a port context:
631 my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF; 708 my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
646 723
647sub _spawn { 724sub _spawn {
648 my $port = shift; 725 my $port = shift;
649 my $init = shift; 726 my $init = shift;
650 727
728 # rcv will create the actual port
651 local $SELF = "$NODE#$port"; 729 local $SELF = "$NODE#$port";
652 eval { 730 eval {
653 &{ load_func $init } 731 &{ load_func $init }
654 }; 732 };
655 _self_die if $@; 733 _self_die if $@;
656} 734}
657 735
658sub spawn(@) { 736sub spawn(@) {
659 my ($noderef, undef) = split /#/, shift, 2; 737 my ($nodeid, undef) = split /#/, shift, 2;
660 738
661 my $id = "$RUNIQ." . $ID++; 739 my $id = "$RUNIQ." . $ID++;
662 740
663 $_[0] =~ /::/ 741 $_[0] =~ /::/
664 or Carp::croak "spawn init function must be a fully-qualified name, caught"; 742 or Carp::croak "spawn init function must be a fully-qualified name, caught";
665 743
666 snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_; 744 snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
667 745
668 "$noderef#$id" 746 "$nodeid#$id"
669} 747}
670 748
671=item after $timeout, @msg 749=item after $timeout, @msg
672 750
673=item after $timeout, $callback 751=item after $timeout, $callback
674 752
675Either sends the given message, or call the given callback, after the 753Either sends the given message, or call the given callback, after the
676specified number of seconds. 754specified number of seconds.
677 755
678This is simply a utility function that come sin handy at times. 756This is simply a utility function that comes in handy at times - the
757AnyEvent::MP author is not convinced of the wisdom of having it, though,
758so it may go away in the future.
679 759
680=cut 760=cut
681 761
682sub after($@) { 762sub after($@) {
683 my ($timeout, @action) = @_; 763 my ($timeout, @action) = @_;
688 ? $action[0]() 768 ? $action[0]()
689 : snd @action; 769 : snd @action;
690 }; 770 };
691} 771}
692 772
773=item cal $port, @msg, $callback[, $timeout]
774
775A simple form of RPC - sends a message to the given C<$port> with the
776given contents (C<@msg>), but adds a reply port to the message.
777
778The reply port is created temporarily just for the purpose of receiving
779the reply, and will be C<kil>ed when no longer needed.
780
781A reply message sent to the port is passed to the C<$callback> as-is.
782
783If an optional time-out (in seconds) is given and it is not C<undef>,
784then the callback will be called without any arguments after the time-out
785elapsed and the port is C<kil>ed.
786
787If no time-out is given (or it is C<undef>), then the local port will
788monitor the remote port instead, so it eventually gets cleaned-up.
789
790Currently this function returns the temporary port, but this "feature"
791might go in future versions unless you can make a convincing case that
792this is indeed useful for something.
793
794=cut
795
796sub cal(@) {
797 my $timeout = ref $_[-1] ? undef : pop;
798 my $cb = pop;
799
800 my $port = port {
801 undef $timeout;
802 kil $SELF;
803 &$cb;
804 };
805
806 if (defined $timeout) {
807 $timeout = AE::timer $timeout, 0, sub {
808 undef $timeout;
809 kil $port;
810 $cb->();
811 };
812 } else {
813 mon $_[0], sub {
814 kil $port;
815 $cb->();
816 };
817 }
818
819 push @_, $port;
820 &snd;
821
822 $port
823}
824
693=back 825=back
694 826
695=head1 AnyEvent::MP vs. Distributed Erlang 827=head1 AnyEvent::MP vs. Distributed Erlang
696 828
697AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node 829AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
698== aemp node, Erlang process == aemp port), so many of the documents and 830== aemp node, Erlang process == aemp port), so many of the documents and
699programming techniques employed by Erlang apply to AnyEvent::MP. Here is a 831programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
700sample: 832sample:
701 833
702 http://www.Erlang.se/doc/programming_rules.shtml 834 http://www.erlang.se/doc/programming_rules.shtml
703 http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4 835 http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
704 http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6 836 http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
705 http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5 837 http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
706 838
707Despite the similarities, there are also some important differences: 839Despite the similarities, there are also some important differences:
708 840
709=over 4 841=over 4
710 842
711=item * Node references contain the recipe on how to contact them. 843=item * Node IDs are arbitrary strings in AEMP.
712 844
713Erlang relies on special naming and DNS to work everywhere in the 845Erlang relies on special naming and DNS to work everywhere in the same
714same way. AEMP relies on each node knowing it's own address(es), with 846way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715convenience functionality. 847configuration or DNS), and possibly the addresses of some seed nodes, but
716 848will otherwise discover other nodes (and their IDs) itself.
717This means that AEMP requires a less tightly controlled environment at the
718cost of longer node references and a slightly higher management overhead.
719 849
720=item * Erlang has a "remote ports are like local ports" philosophy, AEMP 850=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721uses "local ports are like remote ports". 851uses "local ports are like remote ports".
722 852
723The failure modes for local ports are quite different (runtime errors 853The failure modes for local ports are quite different (runtime errors
736 866
737Erlang uses processes that selectively receive messages, and therefore 867Erlang uses processes that selectively receive messages, and therefore
738needs a queue. AEMP is event based, queuing messages would serve no 868needs a queue. AEMP is event based, queuing messages would serve no
739useful purpose. For the same reason the pattern-matching abilities of 869useful purpose. For the same reason the pattern-matching abilities of
740AnyEvent::MP are more limited, as there is little need to be able to 870AnyEvent::MP are more limited, as there is little need to be able to
741filter messages without dequeing them. 871filter messages without dequeuing them.
742 872
743(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP). 873(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
744 874
745=item * Erlang sends are synchronous, AEMP sends are asynchronous. 875=item * Erlang sends are synchronous, AEMP sends are asynchronous.
746 876
748so does not need a queue that can overflow). AEMP sends are immediate, 878so does not need a queue that can overflow). AEMP sends are immediate,
749connection establishment is handled in the background. 879connection establishment is handled in the background.
750 880
751=item * Erlang suffers from silent message loss, AEMP does not. 881=item * Erlang suffers from silent message loss, AEMP does not.
752 882
753Erlang makes few guarantees on messages delivery - messages can get lost 883Erlang implements few guarantees on messages delivery - messages can get
754without any of the processes realising it (i.e. you send messages a, b, 884lost without any of the processes realising it (i.e. you send messages a,
755and c, and the other side only receives messages a and c). 885b, and c, and the other side only receives messages a and c).
756 886
757AEMP guarantees correct ordering, and the guarantee that there are no 887AEMP guarantees correct ordering, and the guarantee that after one message
758holes in the message sequence. 888is lost, all following ones sent to the same port are lost as well, until
759 889monitoring raises an error, so there are no silent "holes" in the message
760=item * In Erlang, processes can be declared dead and later be found to be 890sequence.
761alive.
762
763In Erlang it can happen that a monitored process is declared dead and
764linked processes get killed, but later it turns out that the process is
765still alive - and can receive messages.
766
767In AEMP, when port monitoring detects a port as dead, then that port will
768eventually be killed - it cannot happen that a node detects a port as dead
769and then later sends messages to it, finding it is still alive.
770 891
771=item * Erlang can send messages to the wrong port, AEMP does not. 892=item * Erlang can send messages to the wrong port, AEMP does not.
772 893
773In Erlang it is quite likely that a node that restarts reuses a process ID 894In Erlang it is quite likely that a node that restarts reuses a process ID
774known to other nodes for a completely different process, causing messages 895known to other nodes for a completely different process, causing messages
778around in the network will not be sent to an unrelated port. 899around in the network will not be sent to an unrelated port.
779 900
780=item * Erlang uses unprotected connections, AEMP uses secure 901=item * Erlang uses unprotected connections, AEMP uses secure
781authentication and can use TLS. 902authentication and can use TLS.
782 903
783AEMP can use a proven protocol - SSL/TLS - to protect connections and 904AEMP can use a proven protocol - TLS - to protect connections and
784securely authenticate nodes. 905securely authenticate nodes.
785 906
786=item * The AEMP protocol is optimised for both text-based and binary 907=item * The AEMP protocol is optimised for both text-based and binary
787communications. 908communications.
788 909
789The AEMP protocol, unlike the Erlang protocol, supports both 910The AEMP protocol, unlike the Erlang protocol, supports both programming
790language-independent text-only protocols (good for debugging) and binary, 911language independent text-only protocols (good for debugging) and binary,
791language-specific serialisers (e.g. Storable). 912language-specific serialisers (e.g. Storable). By default, unless TLS is
913used, the protocol is actually completely text-based.
792 914
793It has also been carefully designed to be implementable in other languages 915It has also been carefully designed to be implementable in other languages
794with a minimum of work while gracefully degrading fucntionality to make the 916with a minimum of work while gracefully degrading functionality to make the
795protocol simple. 917protocol simple.
796 918
797=item * AEMP has more flexible monitoring options than Erlang. 919=item * AEMP has more flexible monitoring options than Erlang.
798 920
799In Erlang, you can chose to receive I<all> exit signals as messages 921In Erlang, you can chose to receive I<all> exit signals as messages
802Erlang, as one can choose between automatic kill, exit message or callback 924Erlang, as one can choose between automatic kill, exit message or callback
803on a per-process basis. 925on a per-process basis.
804 926
805=item * Erlang tries to hide remote/local connections, AEMP does not. 927=item * Erlang tries to hide remote/local connections, AEMP does not.
806 928
807Monitoring in Erlang is not an indicator of process death/crashes, 929Monitoring in Erlang is not an indicator of process death/crashes, in the
808as linking is (except linking is unreliable in Erlang). 930same way as linking is (except linking is unreliable in Erlang).
809 931
810In AEMP, you don't "look up" registered port names or send to named ports 932In AEMP, you don't "look up" registered port names or send to named ports
811that might or might not be persistent. Instead, you normally spawn a port 933that might or might not be persistent. Instead, you normally spawn a port
812on the remote node. The init function monitors the you, and you monitor 934on the remote node. The init function monitors you, and you monitor the
813the remote port. Since both monitors are local to the node, they are much 935remote port. Since both monitors are local to the node, they are much more
814more reliable. 936reliable (no need for C<spawn_link>).
815 937
816This also saves round-trips and avoids sending messages to the wrong port 938This also saves round-trips and avoids sending messages to the wrong port
817(hard to do in Erlang). 939(hard to do in Erlang).
818 940
819=back 941=back
820 942
821=head1 RATIONALE 943=head1 RATIONALE
822 944
823=over 4 945=over 4
824 946
825=item Why strings for ports and noderefs, why not objects? 947=item Why strings for port and node IDs, why not objects?
826 948
827We considered "objects", but found that the actual number of methods 949We considered "objects", but found that the actual number of methods
828thatc an be called are very low. Since port IDs and noderefs travel over 950that can be called are quite low. Since port and node IDs travel over
829the network frequently, the serialising/deserialising would add lots of 951the network frequently, the serialising/deserialising would add lots of
830overhead, as well as having to keep a proxy object. 952overhead, as well as having to keep a proxy object everywhere.
831 953
832Strings can easily be printed, easily serialised etc. and need no special 954Strings can easily be printed, easily serialised etc. and need no special
833procedures to be "valid". 955procedures to be "valid".
834 956
835And a a miniport consists of a single closure stored in a global hash - it 957And as a result, a miniport consists of a single closure stored in a
836can't become much cheaper. 958global hash - it can't become much cheaper.
837 959
838=item Why favour JSON, why not real serialising format such as Storable? 960=item Why favour JSON, why not a real serialising format such as Storable?
839 961
840In fact, any AnyEvent::MP node will happily accept Storable as framing 962In fact, any AnyEvent::MP node will happily accept Storable as framing
841format, but currently there is no way to make a node use Storable by 963format, but currently there is no way to make a node use Storable by
842default. 964default (although all nodes will accept it).
843 965
844The default framing protocol is JSON because a) JSON::XS is many times 966The default framing protocol is JSON because a) JSON::XS is many times
845faster for small messages and b) most importantly, after years of 967faster for small messages and b) most importantly, after years of
846experience we found that object serialisation is causing more problems 968experience we found that object serialisation is causing more problems
847than it gains: Just like function calls, objects simply do not travel 969than it solves: Just like function calls, objects simply do not travel
848easily over the network, mostly because they will always be a copy, so you 970easily over the network, mostly because they will always be a copy, so you
849always have to re-think your design. 971always have to re-think your design.
850 972
851Keeping your messages simple, concentrating on data structures rather than 973Keeping your messages simple, concentrating on data structures rather than
852objects, will keep your messages clean, tidy and efficient. 974objects, will keep your messages clean, tidy and efficient.
853 975
854=back 976=back
855 977
856=head1 SEE ALSO 978=head1 SEE ALSO
857 979
980L<AnyEvent::MP::Intro> - a gentle introduction.
981
982L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
983
984L<AnyEvent::MP::Global> - network maintainance and port groups, to find
985your applications.
986
987L<AnyEvent::MP::DataConn> - establish data connections between nodes.
988
989L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
990all nodes.
991
858L<AnyEvent>. 992L<AnyEvent>.
859 993
860=head1 AUTHOR 994=head1 AUTHOR
861 995
862 Marc Lehmann <schmorp@schmorp.de> 996 Marc Lehmann <schmorp@schmorp.de>

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