| 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 $portid |
| 129 |
|
| 130 |
Extracts and returns the noderef from a portid or a noderef. |
| 131 |
|
| 132 |
=item $cv = resolve_node $noderef |
| 133 |
|
| 134 |
Takes an unresolved node reference that may contain hostnames and |
| 135 |
abbreviated IDs, resolves all of them and returns a resolved node |
| 136 |
reference. |
| 137 |
|
| 138 |
In addition to C<address:port> pairs allowed in resolved noderefs, the |
| 139 |
following forms are supported: |
| 140 |
|
| 141 |
=over 4 |
| 142 |
|
| 143 |
=item the empty string |
| 144 |
|
| 145 |
An empty-string component gets resolved as if the default port (4040) was |
| 146 |
specified. |
| 147 |
|
| 148 |
=item naked port numbers (e.g. C<1234>) |
| 149 |
|
| 150 |
These are resolved by prepending the local nodename and a colon, to be |
| 151 |
further resolved. |
| 152 |
|
| 153 |
=item hostnames (e.g. C<localhost:1234>, C<localhost>) |
| 154 |
|
| 155 |
These are resolved by using AnyEvent::DNS to resolve them, optionally |
| 156 |
looking up SRV records for the C<aemp=4040> port, if no port was |
| 157 |
specified. |
| 158 |
|
| 159 |
=back |
| 160 |
|
| 161 |
=item $SELF |
| 162 |
|
| 163 |
Contains the current port id while executing C<rcv> callbacks or C<psub> |
| 164 |
blocks. |
| 165 |
|
| 166 |
=item SELF, %SELF, @SELF... |
| 167 |
|
| 168 |
Due to some quirks in how perl exports variables, it is impossible to |
| 169 |
just export C<$SELF>, all the symbols called C<SELF> are exported by this |
| 170 |
module, but only C<$SELF> is currently used. |
| 171 |
|
| 172 |
=item snd $portid, type => @data |
| 173 |
|
| 174 |
=item snd $portid, @msg |
| 175 |
|
| 176 |
Send the given message to the given port ID, which can identify either |
| 177 |
a local or a remote port, and can be either a string or soemthignt hat |
| 178 |
stringifies a sa port ID (such as a port object :). |
| 179 |
|
| 180 |
While the message can be about anything, it is highly recommended to use a |
| 181 |
string as first element (a portid, or some word that indicates a request |
| 182 |
type etc.). |
| 183 |
|
| 184 |
The message data effectively becomes read-only after a call to this |
| 185 |
function: modifying any argument is not allowed and can cause many |
| 186 |
problems. |
| 187 |
|
| 188 |
The type of data you can transfer depends on the transport protocol: when |
| 189 |
JSON is used, then only strings, numbers and arrays and hashes consisting |
| 190 |
of those are allowed (no objects). When Storable is used, then anything |
| 191 |
that Storable can serialise and deserialise is allowed, and for the local |
| 192 |
node, anything can be passed. |
| 193 |
|
| 194 |
=item kil $portid[, @reason] |
| 195 |
|
| 196 |
Kill the specified port with the given C<@reason>. |
| 197 |
|
| 198 |
If no C<@reason> is specified, then the port is killed "normally" (linked |
| 199 |
ports will not be kileld, or even notified). |
| 200 |
|
| 201 |
Otherwise, linked ports get killed with the same reason (second form of |
| 202 |
C<mon>, see below). |
| 203 |
|
| 204 |
Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks |
| 205 |
will be reported as reason C<< die => $@ >>. |
| 206 |
|
| 207 |
Transport/communication errors are reported as C<< transport_error => |
| 208 |
$message >>. |
| 209 |
|
| 210 |
=item $guard = mon $portid, $cb->(@reason) |
| 211 |
|
| 212 |
=item $guard = mon $portid, $otherport |
| 213 |
|
| 214 |
=item $guard = mon $portid, $otherport, @msg |
| 215 |
|
| 216 |
Monitor the given port and do something when the port is killed. |
| 217 |
|
| 218 |
In the first form, the callback is simply called with any number |
| 219 |
of C<@reason> elements (no @reason means that the port was deleted |
| 220 |
"normally"). Note also that I<< the callback B<must> never die >>, so use |
| 221 |
C<eval> if unsure. |
| 222 |
|
| 223 |
In the second form, the other port will be C<kil>'ed with C<@reason>, iff |
| 224 |
a @reason was specified, i.e. on "normal" kils nothing happens, while |
| 225 |
under all other conditions, the other port is killed with the same reason. |
| 226 |
|
| 227 |
In the last form, a message of the form C<@msg, @reason> will be C<snd>. |
| 228 |
|
| 229 |
Example: call a given callback when C<$port> is killed. |
| 230 |
|
| 231 |
mon $port, sub { warn "port died because of <@_>\n" }; |
| 232 |
|
| 233 |
Example: kill ourselves when C<$port> is killed abnormally. |
| 234 |
|
| 235 |
mon $port, $self; |
| 236 |
|
| 237 |
Example: send us a restart message another C<$port> is killed. |
| 238 |
|
| 239 |
mon $port, $self => "restart"; |
| 240 |
|
| 241 |
=cut |
| 242 |
|
| 243 |
sub mon { |
| 244 |
my ($noderef, $port) = split /#/, shift, 2; |
| 245 |
|
| 246 |
my $node = $NODE{$noderef} || add_node $noderef; |
| 247 |
|
| 248 |
my $cb = shift; |
| 249 |
|
| 250 |
unless (ref $cb) { |
| 251 |
if (@_) { |
| 252 |
# send a kill info message |
| 253 |
my (@msg) = ($cb, @_); |
| 254 |
$cb = sub { snd @msg, @_ }; |
| 255 |
} else { |
| 256 |
# simply kill other port |
| 257 |
my $port = $cb; |
| 258 |
$cb = sub { kil $port, @_ if @_ }; |
| 259 |
} |
| 260 |
} |
| 261 |
|
| 262 |
$node->monitor ($port, $cb); |
| 263 |
|
| 264 |
defined wantarray |
| 265 |
and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) } |
| 266 |
} |
| 267 |
|
| 268 |
=item $guard = mon_guard $port, $ref, $ref... |
| 269 |
|
| 270 |
Monitors the given C<$port> and keeps the passed references. When the port |
| 271 |
is killed, the references will be freed. |
| 272 |
|
| 273 |
Optionally returns a guard that will stop the monitoring. |
| 274 |
|
| 275 |
This function is useful when you create e.g. timers or other watchers and |
| 276 |
want to free them when the port gets killed: |
| 277 |
|
| 278 |
$port->rcv (start => sub { |
| 279 |
my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { |
| 280 |
undef $timer if 0.9 < rand; |
| 281 |
}); |
| 282 |
}); |
| 283 |
|
| 284 |
=cut |
| 285 |
|
| 286 |
sub mon_guard { |
| 287 |
my ($port, @refs) = @_; |
| 288 |
|
| 289 |
mon $port, sub { 0 && @refs } |
| 290 |
} |
| 291 |
|
| 292 |
=item lnk $port1, $port2 |
| 293 |
|
| 294 |
Link two ports. This is simply a shorthand for: |
| 295 |
|
| 296 |
mon $port1, $port2; |
| 297 |
mon $port2, $port1; |
| 298 |
|
| 299 |
It means that if either one is killed abnormally, the other one gets |
| 300 |
killed as well. |
| 301 |
|
| 302 |
=item $local_port = port |
| 303 |
|
| 304 |
Create a new local port object that can be used either as a pattern |
| 305 |
matching port ("full port") or a single-callback port ("miniport"), |
| 306 |
depending on how C<rcv> callbacks are bound to the object. |
| 307 |
|
| 308 |
=item $portid = port { my @msg = @_; $finished } |
| 309 |
|
| 310 |
Creates a "mini port", that is, a very lightweight port without any |
| 311 |
pattern matching behind it, and returns its ID. |
| 312 |
|
| 313 |
The block will be called for every message received on the port. When the |
| 314 |
callback returns a true value its job is considered "done" and the port |
| 315 |
will be destroyed. Otherwise it will stay alive. |
| 316 |
|
| 317 |
The message will be passed as-is, no extra argument (i.e. no port id) will |
| 318 |
be passed to the callback. |
| 319 |
|
| 320 |
If you need the local port id in the callback, this works nicely: |
| 321 |
|
| 322 |
my $port; $port = port { |
| 323 |
snd $otherport, reply => $port; |
| 324 |
}; |
| 325 |
|
| 326 |
=cut |
| 327 |
|
| 328 |
sub port(;&) { |
| 329 |
my $id = "$UNIQ." . $ID++; |
| 330 |
my $port = "$NODE#$id"; |
| 331 |
|
| 332 |
if (@_) { |
| 333 |
my $cb = shift; |
| 334 |
$PORT{$id} = sub { |
| 335 |
local $SELF = $port; |
| 336 |
eval { |
| 337 |
&$cb |
| 338 |
and kil $id; |
| 339 |
}; |
| 340 |
_self_die if $@; |
| 341 |
}; |
| 342 |
} else { |
| 343 |
my $self = bless { |
| 344 |
id => "$NODE#$id", |
| 345 |
}, "AnyEvent::MP::Port"; |
| 346 |
|
| 347 |
$PORT_DATA{$id} = $self; |
| 348 |
$PORT{$id} = sub { |
| 349 |
local $SELF = $port; |
| 350 |
|
| 351 |
eval { |
| 352 |
for (@{ $self->{rc0}{$_[0]} }) { |
| 353 |
$_ && &{$_->[0]} |
| 354 |
&& undef $_; |
| 355 |
} |
| 356 |
|
| 357 |
for (@{ $self->{rcv}{$_[0]} }) { |
| 358 |
$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1] |
| 359 |
&& &{$_->[0]} |
| 360 |
&& undef $_; |
| 361 |
} |
| 362 |
|
| 363 |
for (@{ $self->{any} }) { |
| 364 |
$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1] |
| 365 |
&& &{$_->[0]} |
| 366 |
&& undef $_; |
| 367 |
} |
| 368 |
}; |
| 369 |
_self_die if $@; |
| 370 |
}; |
| 371 |
} |
| 372 |
|
| 373 |
$port |
| 374 |
} |
| 375 |
|
| 376 |
=item reg $portid, $name |
| 377 |
|
| 378 |
Registers the given port under the name C<$name>. If the name already |
| 379 |
exists it is replaced. |
| 380 |
|
| 381 |
A port can only be registered under one well known name. |
| 382 |
|
| 383 |
A port automatically becomes unregistered when it is killed. |
| 384 |
|
| 385 |
=cut |
| 386 |
|
| 387 |
sub reg(@) { |
| 388 |
my ($portid, $name) = @_; |
| 389 |
|
| 390 |
$REG{$name} = $portid; |
| 391 |
} |
| 392 |
|
| 393 |
=item rcv $portid, $callback->(@msg) |
| 394 |
|
| 395 |
Replaces the callback on the specified miniport (or newly created port |
| 396 |
object, see C<port>). Full ports are configured with the following calls: |
| 397 |
|
| 398 |
=item rcv $portid, tagstring => $callback->(@msg), ... |
| 399 |
|
| 400 |
=item rcv $portid, $smartmatch => $callback->(@msg), ... |
| 401 |
|
| 402 |
=item rcv $portid, [$smartmatch...] => $callback->(@msg), ... |
| 403 |
|
| 404 |
Register callbacks to be called on matching messages on the given port. |
| 405 |
|
| 406 |
The callback has to return a true value when its work is done, after |
| 407 |
which is will be removed, or a false value in which case it will stay |
| 408 |
registered. |
| 409 |
|
| 410 |
The global C<$SELF> (exported by this module) contains C<$portid> while |
| 411 |
executing the callback. |
| 412 |
|
| 413 |
Runtime errors wdurign callback execution will result in the port being |
| 414 |
C<kil>ed. |
| 415 |
|
| 416 |
If the match is an array reference, then it will be matched against the |
| 417 |
first elements of the message, otherwise only the first element is being |
| 418 |
matched. |
| 419 |
|
| 420 |
Any element in the match that is specified as C<_any_> (a function |
| 421 |
exported by this module) matches any single element of the message. |
| 422 |
|
| 423 |
While not required, it is highly recommended that the first matching |
| 424 |
element is a string identifying the message. The one-string-only match is |
| 425 |
also the most efficient match (by far). |
| 426 |
|
| 427 |
=cut |
| 428 |
|
| 429 |
sub rcv($@) { |
| 430 |
my $portid = shift; |
| 431 |
my ($noderef, $port) = split /#/, $port, 2; |
| 432 |
|
| 433 |
($NODE{$noderef} || add_node $noderef) == $NODE{""} |
| 434 |
or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught"; |
| 435 |
|
| 436 |
my $self = $PORT_DATA{$port} |
| 437 |
or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught"; |
| 438 |
|
| 439 |
"AnyEvent::MP::Port" eq ref $self |
| 440 |
or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught"; |
| 441 |
|
| 442 |
while (@_) { |
| 443 |
my ($match, $cb) = splice @_, 0, 2; |
| 444 |
|
| 445 |
if (!ref $match) { |
| 446 |
push @{ $self->{rc0}{$match} }, [$cb]; |
| 447 |
} elsif (("ARRAY" eq ref $match && !ref $match->[0])) { |
| 448 |
my ($type, @match) = @$match; |
| 449 |
@match |
| 450 |
? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match] |
| 451 |
: push @{ $self->{rc0}{$match->[0]} }, [$cb]; |
| 452 |
} else { |
| 453 |
push @{ $self->{any} }, [$cb, $match]; |
| 454 |
} |
| 455 |
} |
| 456 |
|
| 457 |
$portid |
| 458 |
} |
| 459 |
|
| 460 |
=item $closure = psub { BLOCK } |
| 461 |
|
| 462 |
Remembers C<$SELF> and creates a closure out of the BLOCK. When the |
| 463 |
closure is executed, sets up the environment in the same way as in C<rcv> |
| 464 |
callbacks, i.e. runtime errors will cause the port to get C<kil>ed. |
| 465 |
|
| 466 |
This is useful when you register callbacks from C<rcv> callbacks: |
| 467 |
|
| 468 |
rcv delayed_reply => sub { |
| 469 |
my ($delay, @reply) = @_; |
| 470 |
my $timer = AE::timer $delay, 0, psub { |
| 471 |
snd @reply, $SELF; |
| 472 |
}; |
| 473 |
}; |
| 474 |
|
| 475 |
=cut |
| 476 |
|
| 477 |
sub psub(&) { |
| 478 |
my $cb = shift; |
| 479 |
|
| 480 |
my $port = $SELF |
| 481 |
or Carp::croak "psub can only be called from within rcv or psub callbacks, not"; |
| 482 |
|
| 483 |
sub { |
| 484 |
local $SELF = $port; |
| 485 |
|
| 486 |
if (wantarray) { |
| 487 |
my @res = eval { &$cb }; |
| 488 |
_self_die if $@; |
| 489 |
@res |
| 490 |
} else { |
| 491 |
my $res = eval { &$cb }; |
| 492 |
_self_die if $@; |
| 493 |
$res |
| 494 |
} |
| 495 |
} |
| 496 |
} |
| 497 |
|
| 498 |
=back |
| 499 |
|
| 500 |
=head1 FUNCTIONS FOR NODES |
| 501 |
|
| 502 |
=over 4 |
| 503 |
|
| 504 |
=item become_public $noderef |
| 505 |
|
| 506 |
Tells the node to become a public node, i.e. reachable from other nodes. |
| 507 |
|
| 508 |
The first argument is the (unresolved) node reference of the local node |
| 509 |
(if missing then the empty string is used). |
| 510 |
|
| 511 |
It is quite common to not specify anything, in which case the local node |
| 512 |
tries to listen on the default port, or to only specify a port number, in |
| 513 |
which case AnyEvent::MP tries to guess the local addresses. |
| 514 |
|
| 515 |
=cut |
| 516 |
|
| 517 |
=back |
| 518 |
|
| 519 |
=head1 NODE MESSAGES |
| 520 |
|
| 521 |
Nodes understand the following messages sent to them. Many of them take |
| 522 |
arguments called C<@reply>, which will simply be used to compose a reply |
| 523 |
message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and |
| 524 |
the remaining arguments are simply the message data. |
| 525 |
|
| 526 |
While other messages exist, they are not public and subject to change. |
| 527 |
|
| 528 |
=over 4 |
| 529 |
|
| 530 |
=cut |
| 531 |
|
| 532 |
=item lookup => $name, @reply |
| 533 |
|
| 534 |
Replies with the port ID of the specified well-known port, or C<undef>. |
| 535 |
|
| 536 |
=item devnull => ... |
| 537 |
|
| 538 |
Generic data sink/CPU heat conversion. |
| 539 |
|
| 540 |
=item relay => $port, @msg |
| 541 |
|
| 542 |
Simply forwards the message to the given port. |
| 543 |
|
| 544 |
=item eval => $string[ @reply] |
| 545 |
|
| 546 |
Evaluates the given string. If C<@reply> is given, then a message of the |
| 547 |
form C<@reply, $@, @evalres> is sent. |
| 548 |
|
| 549 |
Example: crash another node. |
| 550 |
|
| 551 |
snd $othernode, eval => "exit"; |
| 552 |
|
| 553 |
=item time => @reply |
| 554 |
|
| 555 |
Replies the the current node time to C<@reply>. |
| 556 |
|
| 557 |
Example: tell the current node to send the current time to C<$myport> in a |
| 558 |
C<timereply> message. |
| 559 |
|
| 560 |
snd $NODE, time => $myport, timereply => 1, 2; |
| 561 |
# => snd $myport, timereply => 1, 2, <time> |
| 562 |
|
| 563 |
=back |
| 564 |
|
| 565 |
=head1 AnyEvent::MP vs. Distributed Erlang |
| 566 |
|
| 567 |
AnyEvent::MP got lots of its ideas from distributed erlang (erlang node |
| 568 |
== aemp node, erlang process == aemp port), so many of the documents and |
| 569 |
programming techniques employed by erlang apply to AnyEvent::MP. Here is a |
| 570 |
sample: |
| 571 |
|
| 572 |
http://www.erlang.se/doc/programming_rules.shtml |
| 573 |
http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4 |
| 574 |
http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6 |
| 575 |
http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5 |
| 576 |
|
| 577 |
Despite the similarities, there are also some important differences: |
| 578 |
|
| 579 |
=over 4 |
| 580 |
|
| 581 |
=item * Node references contain the recipe on how to contact them. |
| 582 |
|
| 583 |
Erlang relies on special naming and DNS to work everywhere in the |
| 584 |
same way. AEMP relies on each node knowing it's own address(es), with |
| 585 |
convenience functionality. |
| 586 |
|
| 587 |
This means that AEMP requires a less tightly controlled environment at the |
| 588 |
cost of longer node references and a slightly higher management overhead. |
| 589 |
|
| 590 |
=item * Erlang uses processes and a mailbox, AEMP does not queue. |
| 591 |
|
| 592 |
Erlang uses processes that selctively receive messages, and therefore |
| 593 |
needs a queue. AEMP is event based, queuing messages would serve no useful |
| 594 |
purpose. |
| 595 |
|
| 596 |
(But see L<Coro::MP> for a more erlang-like process model on top of AEMP). |
| 597 |
|
| 598 |
=item * Erlang sends are synchronous, AEMP sends are asynchronous. |
| 599 |
|
| 600 |
Sending messages in erlang is synchronous and blocks the process. AEMP |
| 601 |
sends are immediate, connection establishment is handled in the |
| 602 |
background. |
| 603 |
|
| 604 |
=item * Erlang can silently lose messages, AEMP cannot. |
| 605 |
|
| 606 |
Erlang makes few guarantees on messages delivery - messages can get lost |
| 607 |
without any of the processes realising it (i.e. you send messages a, b, |
| 608 |
and c, and the other side only receives messages a and c). |
| 609 |
|
| 610 |
AEMP guarantees correct ordering, and the guarantee that there are no |
| 611 |
holes in the message sequence. |
| 612 |
|
| 613 |
=item * In erlang, processes can be declared dead and later be found to be |
| 614 |
alive. |
| 615 |
|
| 616 |
In erlang it can happen that a monitored process is declared dead and |
| 617 |
linked processes get killed, but later it turns out that the process is |
| 618 |
still alive - and can receive messages. |
| 619 |
|
| 620 |
In AEMP, when port monitoring detects a port as dead, then that port will |
| 621 |
eventually be killed - it cannot happen that a node detects a port as dead |
| 622 |
and then later sends messages to it, finding it is still alive. |
| 623 |
|
| 624 |
=item * Erlang can send messages to the wrong port, AEMP does not. |
| 625 |
|
| 626 |
In erlang it is quite possible that a node that restarts reuses a process |
| 627 |
ID known to other nodes for a completely different process, causing |
| 628 |
messages destined for that process to end up in an unrelated process. |
| 629 |
|
| 630 |
AEMP never reuses port IDs, so old messages or old port IDs floating |
| 631 |
around in the network will not be sent to an unrelated port. |
| 632 |
|
| 633 |
=item * Erlang uses unprotected connections, AEMP uses secure |
| 634 |
authentication and can use TLS. |
| 635 |
|
| 636 |
AEMP can use a proven protocol - SSL/TLS - to protect connections and |
| 637 |
securely authenticate nodes. |
| 638 |
|
| 639 |
=item * The AEMP protocol is optimised for both text-based and binary |
| 640 |
communications. |
| 641 |
|
| 642 |
The AEMP protocol, unlike the erlang protocol, supports both |
| 643 |
language-independent text-only protocols (good for debugging) and binary, |
| 644 |
language-specific serialisers (e.g. Storable). |
| 645 |
|
| 646 |
It has also been carefully designed to be implementable in other languages |
| 647 |
with a minimum of work while gracefully degrading fucntionality to make the |
| 648 |
protocol simple. |
| 649 |
|
| 650 |
=back |
| 651 |
|
| 652 |
=head1 SEE ALSO |
| 653 |
|
| 654 |
L<AnyEvent>. |
| 655 |
|
| 656 |
=head1 AUTHOR |
| 657 |
|
| 658 |
Marc Lehmann <schmorp@schmorp.de> |
| 659 |
http://home.schmorp.de/ |
| 660 |
|
| 661 |
=cut |
| 662 |
|
| 663 |
1 |
| 664 |
|
