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