AnyEvent-MP
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=head1 NAME
AnyEvent::MP - erlang-style multi-processing/message-passing framework
=head1 SYNOPSIS
use AnyEvent::MP;
$NODE # contains this node's node ID
NODE # returns this node's node ID
$SELF # receiving/own port id in rcv callbacks
# initialise the node so it can send/receive messages
configure;
# ports are message destinations
# sending messages
snd $port, type => data...;
snd $port, @msg;
snd @msg_with_first_element_being_a_port;
# creating/using ports, the simple way
my $simple_port = port { my @msg = @_ };
# creating/using ports, tagged message matching
my $port = port;
rcv $port, ping => sub { snd $_[0], "pong" };
rcv $port, pong => sub { warn "pong received\n" };
# create a port on another node
my $port = spawn $node, $initfunc, @initdata;
# destroy a port again
kil $port; # "normal" kill
kil $port, my_error => "everything is broken"; # error kill
# monitoring
mon $port, $cb->(@msg) # callback is invoked on death
mon $port, $localport # kill localport on abnormal death
mon $port, $localport, @msg # send message on death
# temporarily execute code in port context
peval $port, sub { die "kill the port!" };
# execute callbacks in $SELF port context
my $timer = AE::timer 1, 0, psub {
die "kill the port, delayed";
};
# distributed database - modification
db_set $family => $subkey [=> $value] # add a subkey
db_del $family => $subkey... # delete one or more subkeys
db_reg $family => $port [=> $value] # register a port
# distributed database - queries
db_family $family => $cb->(\%familyhash)
db_keys $family => $cb->(\@keys)
db_values $family => $cb->(\@values)
# distributed database - monitoring a family
db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
=head1 DESCRIPTION
This module (-family) implements a simple message passing framework.
Despite its simplicity, you can securely message other processes running
on the same or other hosts, and you can supervise entities remotely.
For an introduction to this module family, see the L<AnyEvent::MP::Intro>
manual page and the examples under F<eg/>.
=head1 CONCEPTS
=over 4
=item port
Not to be confused with a TCP port, a "port" is something you can send
messages to (with the C<snd> function).
Ports allow you to register C<rcv> handlers that can match all or just
some messages. Messages send to ports will not be queued, regardless of
anything was listening for them or not.
Ports are represented by (printable) strings called "port IDs".
=item port ID - C<nodeid#portname>
A port ID is the concatenation of a node ID, a hash-mark (C<#>)
as separator, and a port name (a printable string of unspecified
format created by AnyEvent::MP).
=item node
A node is a single process containing at least one port - the node port,
which enables nodes to manage each other remotely, and to create new
ports.
Nodes are either public (have one or more listening ports) or private
(no listening ports). Private nodes cannot talk to other private nodes
currently, but all nodes can talk to public nodes.
Nodes is represented by (printable) strings called "node IDs".
=item node ID - C<[A-Za-z0-9_\-.:]*>
$self->[1]{$tag} = $cb;
} else {
delete $self->[1]{$tag};
}
}
}
$port
}
=item peval $port, $coderef[, @args]
Evaluates the given C<$codref> within the context of C<$port>, that is,
when the code throws an exception the C<$port> will be killed.
Any remaining args will be passed to the callback. Any return values will
be returned to the caller.
This is useful when you temporarily want to execute code in the context of
a port.
Example: create a port and run some initialisation code in it's context.
my $port = port { ... };
peval $port, sub {
init
or die "unable to init";
};
=cut
sub peval($$) {
local $SELF = shift;
my $cb = shift;
if (wantarray) {
my @res = eval { &$cb };
_self_die if $@;
@res
} else {
my $res = eval { &$cb };
_self_die if $@;
$res
}
}
=item $closure = psub { BLOCK }
Remembers C<$SELF> and creates a closure out of the BLOCK. When the
closure is executed, sets up the environment in the same way as in C<rcv>
callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
The effect is basically as if it returned C<< sub { peval $SELF, sub {
BLOCK }, @_ } >>.
This is useful when you register callbacks from C<rcv> callbacks:
rcv delayed_reply => sub {
my ($delay, @reply) = @_;
my $timer = AE::timer $delay, 0, psub {
snd @reply, $SELF;
};
};
=cut
sub psub(&) {
my $cb = shift;
my $port = $SELF
or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
sub {
local $SELF = $port;
if (wantarray) {
my @res = eval { &$cb };
_self_die if $@;
@res
} else {
my $res = eval { &$cb };
_self_die if $@;
$res
}
}
}
=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
=item $guard = mon $port # kill $SELF when $port dies
=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
Monitor the given port and do something when the port is killed or
messages to it were lost, and optionally return a guard that can be used
to stop monitoring again.
The first two forms distinguish between "normal" and "abnormal" kil's:
In the first form (another port given), if the C<$port> is C<kil>'ed with
a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
same reason. That is, on "normal" kil's nothing happens, while under all
other conditions, the other port is killed with the same reason.
The second form (kill self) is the same as the first form, except that
C<$rvport> defaults to C<$SELF>.
The remaining forms don't distinguish between "normal" and "abnormal" kil's
- it's up to the callback or receiver to check whether the C<@reason> is
empty and act accordingly.
In the third form (callback), the callback is simply called with any
number of C<@reason> elements (empty @reason means that the port was deleted
"normally"). Note also that I<< the callback B<must> never die >>, so use
C<eval> if unsure.
In the last form (message), a message of the form C<$rcvport, @msg,
@reason> will be C<snd>.
loss has been detected. No messages will be lost "in between" (after
the first lost message no further messages will be received by the
port). After the monitoring action was invoked, further messages might get
delivered again.
Inter-host-connection timeouts and monitoring depend on the transport
used. The only transport currently implemented is TCP, and AnyEvent::MP
relies on TCP to detect node-downs (this can take 10-15 minutes on a
non-idle connection, and usually around two hours for idle connections).
This means that monitoring is good for program errors and cleaning up
stuff eventually, but they are no replacement for a timeout when you need
to ensure some maximum latency.
Example: call a given callback when C<$port> is killed.
mon $port, sub { warn "port died because of <@_>\n" };
Example: kill ourselves when C<$port> is killed abnormally.
mon $port;
Example: send us a restart message when another C<$port> is killed.
mon $port, $self => "restart";
=cut
sub mon {
my ($nodeid, $port) = split /#/, shift, 2;
my $node = $NODE{$nodeid} || add_node $nodeid;
my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
unless (ref $cb) {
if (@_) {
# send a kill info message
my (@msg) = ($cb, @_);
$cb = sub { snd @msg, @_ };
} else {
# simply kill other port
my $port = $cb;
$cb = sub { kil $port, @_ if @_ };
}
}
$node->monitor ($port, $cb);
defined wantarray
and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
}
=item $guard = mon_guard $port, $ref, $ref...
Monitors the given C<$port> and keeps the passed references. When the port
is killed, the references will be freed.
Optionally returns a guard that will stop the monitoring.
This function is useful when you create e.g. timers or other watchers and
want to free them when the port gets killed (note the use of C<psub>):
$port->rcv (start => sub {
my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
undef $timer if 0.9 < rand;
});
});
=cut
sub mon_guard {
my ($port, @refs) = @_;
#TODO: mon-less form?
mon $port, sub { 0 && @refs }
}
=item kil $port[, @reason]
Kill the specified port with the given C<@reason>.
If no C<@reason> is specified, then the port is killed "normally" -
monitor callback will be invoked, but the kil will not cause linked ports
(C<mon $mport, $lport> form) to get killed.
If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
form) get killed with the same reason.
Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
will be reported as reason C<< die => $@ >>.
Transport/communication errors are reported as C<< transport_error =>
$message >>.
Common idioms:
# silently remove yourself, do not kill linked ports
kil $SELF;
# report a failure in some detail
kil $SELF, failure_mode_1 => "it failed with too high temperature";
# do not waste much time with killing, just die when something goes wrong
open my $fh, "<file"
or die "file: $!";
=item $port = spawn $node, $initfunc[, @initdata]
Creates a port on the node C<$node> (which can also be a port ID, in which
case it's the node where that port resides).
The port ID of the newly created port is returned immediately, and it is
possible to immediately start sending messages or to monitor the port.
After the port has been created, the init function is called on the remote
node, in the same context as a C<rcv> callback. This function must be a
fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
specify a function in the main program, use C<::name>.
If the function doesn't exist, then the node tries to C<require>
the package, then the package above the package and so on (e.g.
C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
exists or it runs out of package names.
# this node, executed from within a port context:
my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
mon $server;
# init function on C<$othernode>
sub connect {
my ($srcport) = @_;
mon $srcport;
rcv $SELF, sub {
...
};
}
=cut
sub _spawn {
my $port = shift;
my $init = shift;
# rcv will create the actual port
local $SELF = "$NODE#$port";
eval {
&{ load_func $init }
};
_self_die if $@;
}
sub spawn(@) {
my ($nodeid, undef) = split /#/, shift, 2;
my $id = $RUNIQ . ++$ID;
$_[0] =~ /::/
or Carp::croak "spawn init function must be a fully-qualified name, caught";
snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
"$nodeid#$id"
}
=item after $timeout, @msg
=item after $timeout, $callback
Either sends the given message, or call the given callback, after the
specified number of seconds.
This is simply a utility function that comes in handy at times - the
AnyEvent::MP author is not convinced of the wisdom of having it, though,
so it may go away in the future.
=cut
sub after($@) {
my ($timeout, @action) = @_;
my $t; $t = AE::timer $timeout, 0, sub {
undef $t;
ref $action[0]
? $action[0]()
: snd @action;
};
}
#=item $cb2 = timeout $seconds, $cb[, @args]
=item cal $port, @msg, $callback[, $timeout]
A simple form of RPC - sends a message to the given C<$port> with the
given contents (C<@msg>), but adds a reply port to the message.
The reply port is created temporarily just for the purpose of receiving
the reply, and will be C<kil>ed when no longer needed.
A reply message sent to the port is passed to the C<$callback> as-is.
If an optional time-out (in seconds) is given and it is not C<undef>,
then the callback will be called without any arguments after the time-out
elapsed and the port is C<kil>ed.
If no time-out is given (or it is C<undef>), then the local port will
monitor the remote port instead, so it eventually gets cleaned-up.
Currently this function returns the temporary port, but this "feature"
might go in future versions unless you can make a convincing case that
this is indeed useful for something.
=cut
sub cal(@) {
my $timeout = ref $_[-1] ? undef : pop;
my $cb = pop;
my $port = port {
undef $timeout;
kil $SELF;
&$cb;
};
if (defined $timeout) {
$timeout = AE::timer $timeout, 0, sub {
undef $timeout;
kil $port;
$cb->();
};
} else {
mon $_[0], sub {
kil $port;
$cb->();
};
}
push @_, $port;
&snd;
$port
}
=back
=head1 DISTRIBUTED DATABASE
AnyEvent::MP comes with a simple distributed database. The database will
be mirrored asynchronously on all global nodes. Other nodes bind to one
of the global nodes for their needs. Every node has a "local database"
which contains all the values that are set locally. All local databases
are merged together to form the global database, which can be queried.
The database structure is that of a two-level hash - the database hash
contains hashes which contain values, similarly to a perl hash of hashes,
i.e.:
$DATABASE{$family}{$subkey} = $value
The top level hash key is called "family", and the second-level hash key
is called "subkey" or simply "key".
The family must be alphanumeric, i.e. start with a letter and consist
of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
pretty much like Perl module names.
As the family namespace is global, it is recommended to prefix family names
with the name of the application or module using it.
The subkeys must be non-empty strings, with no further restrictions.
The values should preferably be strings, but other perl scalars should
work as well (such as C<undef>, arrays and hashes).
Every database entry is owned by one node - adding the same family/subkey
combination on multiple nodes will not cause discomfort for AnyEvent::MP,
but the result might be nondeterministic, i.e. the key might have
different values on different nodes.
Different subkeys in the same family can be owned by different nodes
without problems, and in fact, this is the common method to create worker
pools. For example, a worker port for image scaling might do this:
db_set my_image_scalers => $port;
And clients looking for an image scaler will want to get the
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