1 |
=head1 NAME |
2 |
|
3 |
AnyEvent::MP - multi-processing/message-passing framework |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
use AnyEvent::MP; |
8 |
|
9 |
$NODE # contains this node's noderef |
10 |
NODE # returns this node's noderef |
11 |
NODE $port # returns the noderef of the port |
12 |
|
13 |
snd $port, type => data...; |
14 |
|
15 |
$SELF # receiving/own port id in rcv callbacks |
16 |
|
17 |
rcv $port, smartmatch => $cb->($port, @msg); |
18 |
|
19 |
# examples: |
20 |
rcv $port2, ping => sub { snd $_[0], "pong"; 0 }; |
21 |
rcv $port1, pong => sub { warn "pong received\n" }; |
22 |
snd $port2, ping => $port1; |
23 |
|
24 |
# more, smarter, matches (_any_ is exported by this module) |
25 |
rcv $port, [child_died => $pid] => sub { ... |
26 |
rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3 |
27 |
|
28 |
# linking two ports, so they both crash together |
29 |
lnk $port1, $port2; |
30 |
|
31 |
# monitoring |
32 |
mon $port, $cb->(@msg) # callback is invoked on death |
33 |
mon $port, $otherport # kill otherport on abnormal death |
34 |
mon $port, $otherport, @msg # send message on death |
35 |
|
36 |
=head1 DESCRIPTION |
37 |
|
38 |
This module (-family) implements a simple message passing framework. |
39 |
|
40 |
Despite its simplicity, you can securely message other processes running |
41 |
on the same or other hosts. |
42 |
|
43 |
For an introduction to this module family, see the L<AnyEvent::MP::Intro> |
44 |
manual page. |
45 |
|
46 |
At the moment, this module family is severly broken and underdocumented, |
47 |
so do not use. This was uploaded mainly to reserve the CPAN namespace - |
48 |
stay tuned! The basic API should be finished, however. |
49 |
|
50 |
=head1 CONCEPTS |
51 |
|
52 |
=over 4 |
53 |
|
54 |
=item port |
55 |
|
56 |
A port is something you can send messages to (with the C<snd> function). |
57 |
|
58 |
Some ports allow you to register C<rcv> handlers that can match specific |
59 |
messages. All C<rcv> handlers will receive messages they match, messages |
60 |
will not be queued. |
61 |
|
62 |
=item port id - C<noderef#portname> |
63 |
|
64 |
A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as |
65 |
separator, and a port name (a printable string of unspecified format). An |
66 |
exception is the the node port, whose ID is identical to its node |
67 |
reference. |
68 |
|
69 |
=item node |
70 |
|
71 |
A node is a single process containing at least one port - the node |
72 |
port. You can send messages to node ports to find existing ports or to |
73 |
create new ports, among other things. |
74 |
|
75 |
Nodes are either private (single-process only), slaves (connected to a |
76 |
master node only) or public nodes (connectable from unrelated nodes). |
77 |
|
78 |
=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id> |
79 |
|
80 |
A node reference is a string that either simply identifies the node (for |
81 |
private and slave nodes), or contains a recipe on how to reach a given |
82 |
node (for public nodes). |
83 |
|
84 |
This recipe is simply a comma-separated list of C<address:port> pairs (for |
85 |
TCP/IP, other protocols might look different). |
86 |
|
87 |
Node references come in two flavours: resolved (containing only numerical |
88 |
addresses) or unresolved (where hostnames are used instead of addresses). |
89 |
|
90 |
Before using an unresolved node reference in a message you first have to |
91 |
resolve it. |
92 |
|
93 |
=back |
94 |
|
95 |
=head1 VARIABLES/FUNCTIONS |
96 |
|
97 |
=over 4 |
98 |
|
99 |
=cut |
100 |
|
101 |
package AnyEvent::MP; |
102 |
|
103 |
use AnyEvent::MP::Base; |
104 |
|
105 |
use common::sense; |
106 |
|
107 |
use Carp (); |
108 |
|
109 |
use AE (); |
110 |
|
111 |
use base "Exporter"; |
112 |
|
113 |
our $VERSION = '0.1'; |
114 |
our @EXPORT = qw( |
115 |
NODE $NODE *SELF node_of _any_ |
116 |
resolve_node initialise_node |
117 |
snd rcv mon kil reg psub |
118 |
port |
119 |
); |
120 |
|
121 |
our $SELF; |
122 |
|
123 |
sub _self_die() { |
124 |
my $msg = $@; |
125 |
$msg =~ s/\n+$// unless ref $msg; |
126 |
kil $SELF, die => $msg; |
127 |
} |
128 |
|
129 |
=item $thisnode = NODE / $NODE |
130 |
|
131 |
The C<NODE> function returns, and the C<$NODE> variable contains |
132 |
the noderef of the local node. The value is initialised by a call |
133 |
to C<become_public> or C<become_slave>, after which all local port |
134 |
identifiers become invalid. |
135 |
|
136 |
=item $noderef = node_of $port |
137 |
|
138 |
Extracts and returns the noderef from a portid or a noderef. |
139 |
|
140 |
=item initialise_node $noderef, $seednode, $seednode... |
141 |
|
142 |
=item initialise_node "slave/", $master, $master... |
143 |
|
144 |
Before a node can talk to other nodes on the network it has to initialise |
145 |
itself - the minimum a node needs to know is it's own name, and optionally |
146 |
it should know the noderefs of some other nodes in the network. |
147 |
|
148 |
This function initialises a node - it must be called exactly once (or |
149 |
never) before calling other AnyEvent::MP functions. |
150 |
|
151 |
All arguments are noderefs, which can be either resolved or unresolved. |
152 |
|
153 |
There are two types of networked nodes, public nodes and slave nodes: |
154 |
|
155 |
=over 4 |
156 |
|
157 |
=item public nodes |
158 |
|
159 |
For public nodes, C<$noderef> must either be a (possibly unresolved) |
160 |
noderef, in which case it will be resolved, or C<undef> (or missing), in |
161 |
which case the noderef will be guessed. |
162 |
|
163 |
Afterwards, the node will bind itself on all endpoints and try to connect |
164 |
to all additional C<$seednodes> that are specified. Seednodes are optional |
165 |
and can be used to quickly bootstrap the node into an existing network. |
166 |
|
167 |
=item slave nodes |
168 |
|
169 |
When the C<$noderef> is the special string C<slave/>, then the node will |
170 |
become a slave node. Slave nodes cannot be contacted from outside and will |
171 |
route most of their traffic to the master node that they attach to. |
172 |
|
173 |
At least one additional noderef is required: The node will try to connect |
174 |
to all of them and will become a slave attached to the first node it can |
175 |
successfully connect to. |
176 |
|
177 |
=back |
178 |
|
179 |
This function will block until all nodes have been resolved and, for slave |
180 |
nodes, until it has successfully established a connection to a master |
181 |
server. |
182 |
|
183 |
Example: become a public node listening on the default node. |
184 |
|
185 |
initialise_node; |
186 |
|
187 |
Example: become a public node, and try to contact some well-known master |
188 |
servers to become part of the network. |
189 |
|
190 |
initialise_node undef, "master1", "master2"; |
191 |
|
192 |
Example: become a public node listening on port C<4041>. |
193 |
|
194 |
initialise_node 4041; |
195 |
|
196 |
Example: become a public node, only visible on localhost port 4044. |
197 |
|
198 |
initialise_node "locahost:4044"; |
199 |
|
200 |
Example: become a slave node to any of the specified master servers. |
201 |
|
202 |
initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net"; |
203 |
|
204 |
=item $cv = resolve_node $noderef |
205 |
|
206 |
Takes an unresolved node reference that may contain hostnames and |
207 |
abbreviated IDs, resolves all of them and returns a resolved node |
208 |
reference. |
209 |
|
210 |
In addition to C<address:port> pairs allowed in resolved noderefs, the |
211 |
following forms are supported: |
212 |
|
213 |
=over 4 |
214 |
|
215 |
=item the empty string |
216 |
|
217 |
An empty-string component gets resolved as if the default port (4040) was |
218 |
specified. |
219 |
|
220 |
=item naked port numbers (e.g. C<1234>) |
221 |
|
222 |
These are resolved by prepending the local nodename and a colon, to be |
223 |
further resolved. |
224 |
|
225 |
=item hostnames (e.g. C<localhost:1234>, C<localhost>) |
226 |
|
227 |
These are resolved by using AnyEvent::DNS to resolve them, optionally |
228 |
looking up SRV records for the C<aemp=4040> port, if no port was |
229 |
specified. |
230 |
|
231 |
=back |
232 |
|
233 |
=item $SELF |
234 |
|
235 |
Contains the current port id while executing C<rcv> callbacks or C<psub> |
236 |
blocks. |
237 |
|
238 |
=item SELF, %SELF, @SELF... |
239 |
|
240 |
Due to some quirks in how perl exports variables, it is impossible to |
241 |
just export C<$SELF>, all the symbols called C<SELF> are exported by this |
242 |
module, but only C<$SELF> is currently used. |
243 |
|
244 |
=item snd $port, type => @data |
245 |
|
246 |
=item snd $port, @msg |
247 |
|
248 |
Send the given message to the given port ID, which can identify either |
249 |
a local or a remote port, and can be either a string or soemthignt hat |
250 |
stringifies a sa port ID (such as a port object :). |
251 |
|
252 |
While the message can be about anything, it is highly recommended to use a |
253 |
string as first element (a portid, or some word that indicates a request |
254 |
type etc.). |
255 |
|
256 |
The message data effectively becomes read-only after a call to this |
257 |
function: modifying any argument is not allowed and can cause many |
258 |
problems. |
259 |
|
260 |
The type of data you can transfer depends on the transport protocol: when |
261 |
JSON is used, then only strings, numbers and arrays and hashes consisting |
262 |
of those are allowed (no objects). When Storable is used, then anything |
263 |
that Storable can serialise and deserialise is allowed, and for the local |
264 |
node, anything can be passed. |
265 |
|
266 |
=item $local_port = port |
267 |
|
268 |
Create a new local port object that can be used either as a pattern |
269 |
matching port ("full port") or a single-callback port ("miniport"), |
270 |
depending on how C<rcv> callbacks are bound to the object. |
271 |
|
272 |
=item $port = port { my @msg = @_; $finished } |
273 |
|
274 |
Creates a "miniport", that is, a very lightweight port without any pattern |
275 |
matching behind it, and returns its ID. Semantically the same as creating |
276 |
a port and calling C<rcv $port, $callback> on it. |
277 |
|
278 |
The block will be called for every message received on the port. When the |
279 |
callback returns a true value its job is considered "done" and the port |
280 |
will be destroyed. Otherwise it will stay alive. |
281 |
|
282 |
The message will be passed as-is, no extra argument (i.e. no port id) will |
283 |
be passed to the callback. |
284 |
|
285 |
If you need the local port id in the callback, this works nicely: |
286 |
|
287 |
my $port; $port = port { |
288 |
snd $otherport, reply => $port; |
289 |
}; |
290 |
|
291 |
=cut |
292 |
|
293 |
sub rcv($@); |
294 |
|
295 |
sub port(;&) { |
296 |
my $id = "$UNIQ." . $ID++; |
297 |
my $port = "$NODE#$id"; |
298 |
|
299 |
if (@_) { |
300 |
rcv $port, shift; |
301 |
} else { |
302 |
$PORT{$id} = sub { }; # nop |
303 |
} |
304 |
|
305 |
$port |
306 |
} |
307 |
|
308 |
=item reg $port, $name |
309 |
|
310 |
Registers the given port under the name C<$name>. If the name already |
311 |
exists it is replaced. |
312 |
|
313 |
A port can only be registered under one well known name. |
314 |
|
315 |
A port automatically becomes unregistered when it is killed. |
316 |
|
317 |
=cut |
318 |
|
319 |
sub reg(@) { |
320 |
my ($port, $name) = @_; |
321 |
|
322 |
$REG{$name} = $port; |
323 |
} |
324 |
|
325 |
=item rcv $port, $callback->(@msg) |
326 |
|
327 |
Replaces the callback on the specified miniport (after converting it to |
328 |
one if required). |
329 |
|
330 |
=item rcv $port, tagstring => $callback->(@msg), ... |
331 |
|
332 |
=item rcv $port, $smartmatch => $callback->(@msg), ... |
333 |
|
334 |
=item rcv $port, [$smartmatch...] => $callback->(@msg), ... |
335 |
|
336 |
Register callbacks to be called on matching messages on the given full |
337 |
port (after converting it to one if required). |
338 |
|
339 |
The callback has to return a true value when its work is done, after |
340 |
which is will be removed, or a false value in which case it will stay |
341 |
registered. |
342 |
|
343 |
The global C<$SELF> (exported by this module) contains C<$port> while |
344 |
executing the callback. |
345 |
|
346 |
Runtime errors wdurign callback execution will result in the port being |
347 |
C<kil>ed. |
348 |
|
349 |
If the match is an array reference, then it will be matched against the |
350 |
first elements of the message, otherwise only the first element is being |
351 |
matched. |
352 |
|
353 |
Any element in the match that is specified as C<_any_> (a function |
354 |
exported by this module) matches any single element of the message. |
355 |
|
356 |
While not required, it is highly recommended that the first matching |
357 |
element is a string identifying the message. The one-string-only match is |
358 |
also the most efficient match (by far). |
359 |
|
360 |
=cut |
361 |
|
362 |
sub rcv($@) { |
363 |
my $port = shift; |
364 |
my ($noderef, $portid) = split /#/, $port, 2; |
365 |
|
366 |
($NODE{$noderef} || add_node $noderef) == $NODE{""} |
367 |
or Carp::croak "$port: rcv can only be called on local ports, caught"; |
368 |
|
369 |
if (@_ == 1) { |
370 |
my $cb = shift; |
371 |
delete $PORT_DATA{$portid}; |
372 |
$PORT{$portid} = sub { |
373 |
local $SELF = $port; |
374 |
eval { |
375 |
&$cb |
376 |
and kil $port; |
377 |
}; |
378 |
_self_die if $@; |
379 |
}; |
380 |
} else { |
381 |
my $self = $PORT_DATA{$portid} ||= do { |
382 |
my $self = bless { |
383 |
id => $port, |
384 |
}, "AnyEvent::MP::Port"; |
385 |
|
386 |
$PORT{$portid} = sub { |
387 |
local $SELF = $port; |
388 |
|
389 |
eval { |
390 |
for (@{ $self->{rc0}{$_[0]} }) { |
391 |
$_ && &{$_->[0]} |
392 |
&& undef $_; |
393 |
} |
394 |
|
395 |
for (@{ $self->{rcv}{$_[0]} }) { |
396 |
$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1] |
397 |
&& &{$_->[0]} |
398 |
&& undef $_; |
399 |
} |
400 |
|
401 |
for (@{ $self->{any} }) { |
402 |
$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1] |
403 |
&& &{$_->[0]} |
404 |
&& undef $_; |
405 |
} |
406 |
}; |
407 |
_self_die if $@; |
408 |
}; |
409 |
|
410 |
$self |
411 |
}; |
412 |
|
413 |
"AnyEvent::MP::Port" eq ref $self |
414 |
or Carp::croak "$port: rcv can only be called on message matching ports, caught"; |
415 |
|
416 |
while (@_) { |
417 |
my ($match, $cb) = splice @_, 0, 2; |
418 |
|
419 |
if (!ref $match) { |
420 |
push @{ $self->{rc0}{$match} }, [$cb]; |
421 |
} elsif (("ARRAY" eq ref $match && !ref $match->[0])) { |
422 |
my ($type, @match) = @$match; |
423 |
@match |
424 |
? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match] |
425 |
: push @{ $self->{rc0}{$match->[0]} }, [$cb]; |
426 |
} else { |
427 |
push @{ $self->{any} }, [$cb, $match]; |
428 |
} |
429 |
} |
430 |
} |
431 |
|
432 |
$port |
433 |
} |
434 |
|
435 |
=item $closure = psub { BLOCK } |
436 |
|
437 |
Remembers C<$SELF> and creates a closure out of the BLOCK. When the |
438 |
closure is executed, sets up the environment in the same way as in C<rcv> |
439 |
callbacks, i.e. runtime errors will cause the port to get C<kil>ed. |
440 |
|
441 |
This is useful when you register callbacks from C<rcv> callbacks: |
442 |
|
443 |
rcv delayed_reply => sub { |
444 |
my ($delay, @reply) = @_; |
445 |
my $timer = AE::timer $delay, 0, psub { |
446 |
snd @reply, $SELF; |
447 |
}; |
448 |
}; |
449 |
|
450 |
=cut |
451 |
|
452 |
sub psub(&) { |
453 |
my $cb = shift; |
454 |
|
455 |
my $port = $SELF |
456 |
or Carp::croak "psub can only be called from within rcv or psub callbacks, not"; |
457 |
|
458 |
sub { |
459 |
local $SELF = $port; |
460 |
|
461 |
if (wantarray) { |
462 |
my @res = eval { &$cb }; |
463 |
_self_die if $@; |
464 |
@res |
465 |
} else { |
466 |
my $res = eval { &$cb }; |
467 |
_self_die if $@; |
468 |
$res |
469 |
} |
470 |
} |
471 |
} |
472 |
|
473 |
=item $guard = mon $port, $cb->(@reason) |
474 |
|
475 |
=item $guard = mon $port, $otherport |
476 |
|
477 |
=item $guard = mon $port, $otherport, @msg |
478 |
|
479 |
Monitor the given port and do something when the port is killed. |
480 |
|
481 |
In the first form, the callback is simply called with any number |
482 |
of C<@reason> elements (no @reason means that the port was deleted |
483 |
"normally"). Note also that I<< the callback B<must> never die >>, so use |
484 |
C<eval> if unsure. |
485 |
|
486 |
In the second form, the other port will be C<kil>'ed with C<@reason>, iff |
487 |
a @reason was specified, i.e. on "normal" kils nothing happens, while |
488 |
under all other conditions, the other port is killed with the same reason. |
489 |
|
490 |
In the last form, a message of the form C<@msg, @reason> will be C<snd>. |
491 |
|
492 |
Example: call a given callback when C<$port> is killed. |
493 |
|
494 |
mon $port, sub { warn "port died because of <@_>\n" }; |
495 |
|
496 |
Example: kill ourselves when C<$port> is killed abnormally. |
497 |
|
498 |
mon $port, $self; |
499 |
|
500 |
Example: send us a restart message another C<$port> is killed. |
501 |
|
502 |
mon $port, $self => "restart"; |
503 |
|
504 |
=cut |
505 |
|
506 |
sub mon { |
507 |
my ($noderef, $port) = split /#/, shift, 2; |
508 |
|
509 |
my $node = $NODE{$noderef} || add_node $noderef; |
510 |
|
511 |
my $cb = shift; |
512 |
|
513 |
unless (ref $cb) { |
514 |
if (@_) { |
515 |
# send a kill info message |
516 |
my (@msg) = ($cb, @_); |
517 |
$cb = sub { snd @msg, @_ }; |
518 |
} else { |
519 |
# simply kill other port |
520 |
my $port = $cb; |
521 |
$cb = sub { kil $port, @_ if @_ }; |
522 |
} |
523 |
} |
524 |
|
525 |
$node->monitor ($port, $cb); |
526 |
|
527 |
defined wantarray |
528 |
and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) } |
529 |
} |
530 |
|
531 |
=item $guard = mon_guard $port, $ref, $ref... |
532 |
|
533 |
Monitors the given C<$port> and keeps the passed references. When the port |
534 |
is killed, the references will be freed. |
535 |
|
536 |
Optionally returns a guard that will stop the monitoring. |
537 |
|
538 |
This function is useful when you create e.g. timers or other watchers and |
539 |
want to free them when the port gets killed: |
540 |
|
541 |
$port->rcv (start => sub { |
542 |
my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { |
543 |
undef $timer if 0.9 < rand; |
544 |
}); |
545 |
}); |
546 |
|
547 |
=cut |
548 |
|
549 |
sub mon_guard { |
550 |
my ($port, @refs) = @_; |
551 |
|
552 |
mon $port, sub { 0 && @refs } |
553 |
} |
554 |
|
555 |
=item lnk $port1, $port2 |
556 |
|
557 |
Link two ports. This is simply a shorthand for: |
558 |
|
559 |
mon $port1, $port2; |
560 |
mon $port2, $port1; |
561 |
|
562 |
It means that if either one is killed abnormally, the other one gets |
563 |
killed as well. |
564 |
|
565 |
=item kil $port[, @reason] |
566 |
|
567 |
Kill the specified port with the given C<@reason>. |
568 |
|
569 |
If no C<@reason> is specified, then the port is killed "normally" (linked |
570 |
ports will not be kileld, or even notified). |
571 |
|
572 |
Otherwise, linked ports get killed with the same reason (second form of |
573 |
C<mon>, see below). |
574 |
|
575 |
Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks |
576 |
will be reported as reason C<< die => $@ >>. |
577 |
|
578 |
Transport/communication errors are reported as C<< transport_error => |
579 |
$message >>. |
580 |
|
581 |
=back |
582 |
|
583 |
=head1 NODE MESSAGES |
584 |
|
585 |
Nodes understand the following messages sent to them. Many of them take |
586 |
arguments called C<@reply>, which will simply be used to compose a reply |
587 |
message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and |
588 |
the remaining arguments are simply the message data. |
589 |
|
590 |
While other messages exist, they are not public and subject to change. |
591 |
|
592 |
=over 4 |
593 |
|
594 |
=cut |
595 |
|
596 |
=item lookup => $name, @reply |
597 |
|
598 |
Replies with the port ID of the specified well-known port, or C<undef>. |
599 |
|
600 |
=item devnull => ... |
601 |
|
602 |
Generic data sink/CPU heat conversion. |
603 |
|
604 |
=item relay => $port, @msg |
605 |
|
606 |
Simply forwards the message to the given port. |
607 |
|
608 |
=item eval => $string[ @reply] |
609 |
|
610 |
Evaluates the given string. If C<@reply> is given, then a message of the |
611 |
form C<@reply, $@, @evalres> is sent. |
612 |
|
613 |
Example: crash another node. |
614 |
|
615 |
snd $othernode, eval => "exit"; |
616 |
|
617 |
=item time => @reply |
618 |
|
619 |
Replies the the current node time to C<@reply>. |
620 |
|
621 |
Example: tell the current node to send the current time to C<$myport> in a |
622 |
C<timereply> message. |
623 |
|
624 |
snd $NODE, time => $myport, timereply => 1, 2; |
625 |
# => snd $myport, timereply => 1, 2, <time> |
626 |
|
627 |
=back |
628 |
|
629 |
=head1 AnyEvent::MP vs. Distributed Erlang |
630 |
|
631 |
AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node |
632 |
== aemp node, Erlang process == aemp port), so many of the documents and |
633 |
programming techniques employed by Erlang apply to AnyEvent::MP. Here is a |
634 |
sample: |
635 |
|
636 |
http://www.Erlang.se/doc/programming_rules.shtml |
637 |
http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4 |
638 |
http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6 |
639 |
http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5 |
640 |
|
641 |
Despite the similarities, there are also some important differences: |
642 |
|
643 |
=over 4 |
644 |
|
645 |
=item * Node references contain the recipe on how to contact them. |
646 |
|
647 |
Erlang relies on special naming and DNS to work everywhere in the |
648 |
same way. AEMP relies on each node knowing it's own address(es), with |
649 |
convenience functionality. |
650 |
|
651 |
This means that AEMP requires a less tightly controlled environment at the |
652 |
cost of longer node references and a slightly higher management overhead. |
653 |
|
654 |
=item * Erlang uses processes and a mailbox, AEMP does not queue. |
655 |
|
656 |
Erlang uses processes that selctively receive messages, and therefore |
657 |
needs a queue. AEMP is event based, queuing messages would serve no useful |
658 |
purpose. |
659 |
|
660 |
(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP). |
661 |
|
662 |
=item * Erlang sends are synchronous, AEMP sends are asynchronous. |
663 |
|
664 |
Sending messages in Erlang is synchronous and blocks the process. AEMP |
665 |
sends are immediate, connection establishment is handled in the |
666 |
background. |
667 |
|
668 |
=item * Erlang can silently lose messages, AEMP cannot. |
669 |
|
670 |
Erlang makes few guarantees on messages delivery - messages can get lost |
671 |
without any of the processes realising it (i.e. you send messages a, b, |
672 |
and c, and the other side only receives messages a and c). |
673 |
|
674 |
AEMP guarantees correct ordering, and the guarantee that there are no |
675 |
holes in the message sequence. |
676 |
|
677 |
=item * In Erlang, processes can be declared dead and later be found to be |
678 |
alive. |
679 |
|
680 |
In Erlang it can happen that a monitored process is declared dead and |
681 |
linked processes get killed, but later it turns out that the process is |
682 |
still alive - and can receive messages. |
683 |
|
684 |
In AEMP, when port monitoring detects a port as dead, then that port will |
685 |
eventually be killed - it cannot happen that a node detects a port as dead |
686 |
and then later sends messages to it, finding it is still alive. |
687 |
|
688 |
=item * Erlang can send messages to the wrong port, AEMP does not. |
689 |
|
690 |
In Erlang it is quite possible that a node that restarts reuses a process |
691 |
ID known to other nodes for a completely different process, causing |
692 |
messages destined for that process to end up in an unrelated process. |
693 |
|
694 |
AEMP never reuses port IDs, so old messages or old port IDs floating |
695 |
around in the network will not be sent to an unrelated port. |
696 |
|
697 |
=item * Erlang uses unprotected connections, AEMP uses secure |
698 |
authentication and can use TLS. |
699 |
|
700 |
AEMP can use a proven protocol - SSL/TLS - to protect connections and |
701 |
securely authenticate nodes. |
702 |
|
703 |
=item * The AEMP protocol is optimised for both text-based and binary |
704 |
communications. |
705 |
|
706 |
The AEMP protocol, unlike the Erlang protocol, supports both |
707 |
language-independent text-only protocols (good for debugging) and binary, |
708 |
language-specific serialisers (e.g. Storable). |
709 |
|
710 |
It has also been carefully designed to be implementable in other languages |
711 |
with a minimum of work while gracefully degrading fucntionality to make the |
712 |
protocol simple. |
713 |
|
714 |
=item * AEMP has more flexible monitoring options than Erlang. |
715 |
|
716 |
In Erlang, you can chose to receive I<all> exit signals as messages |
717 |
or I<none>, there is no in-between, so monitoring single processes is |
718 |
difficult to implement. Monitoring in AEMP is more flexible than in |
719 |
Erlang, as one can choose between automatic kill, exit message or callback |
720 |
on a per-process basis. |
721 |
|
722 |
=item * Erlang has different semantics for monitoring and linking, AEMP has the same. |
723 |
|
724 |
Monitoring in Erlang is not an indicator of process death/crashes, |
725 |
as linking is (except linking is unreliable in Erlang). In AEMP, the |
726 |
semantics of monitoring and linking are identical, linking is simply |
727 |
two-way monitoring with automatic kill. |
728 |
|
729 |
=back |
730 |
|
731 |
=head1 SEE ALSO |
732 |
|
733 |
L<AnyEvent>. |
734 |
|
735 |
=head1 AUTHOR |
736 |
|
737 |
Marc Lehmann <schmorp@schmorp.de> |
738 |
http://home.schmorp.de/ |
739 |
|
740 |
=cut |
741 |
|
742 |
1 |
743 |
|