AnyEvent-MP
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NAME
AnyEvent::MP - erlang-style multi-processing/message-passing framework
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)
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 AnyEvent::MP::Intro
manual page and the examples under eg/.
CONCEPTS
port
Not to be confused with a TCP port, a "port" is something you can
send messages to (with the "snd" function).
Ports allow you to register "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".
port ID - "nodeid#portname"
A port ID is the concatenation of a node ID, a hash-mark ("#") as
separator, and a port name (a printable string of unspecified format
created by AnyEvent::MP).
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".
node ID - "[A-Za-z0-9_\-.:]*"
A node ID is a string that uniquely identifies the node within a
network. Depending on the configuration used, node IDs can look like
a hostname, a hostname and a port, or a random string. AnyEvent::MP
itself doesn't interpret node IDs in any way except to uniquely
identify a node.
binds - "ip:port"
Example: create a port and bind receivers on it in one go.
my $port = rcv port,
msg1 => sub { ... },
msg2 => sub { ... },
;
Example: create a port, bind receivers and send it in a message
elsewhere in one go:
snd $otherport, reply =>
rcv port,
msg1 => sub { ... },
...
;
Example: temporarily register a rcv callback for a tag matching some
port (e.g. for an rpc reply) and unregister it after a message was
received.
rcv $port, $otherport => sub {
my @reply = @_;
rcv $SELF, $otherport;
};
peval $port, $coderef[, @args]
Evaluates the given $codref within the context of $port, that is,
when the code throws an exception the $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";
};
$closure = psub { BLOCK }
Remembers $SELF and creates a closure out of the BLOCK. When the
closure is executed, sets up the environment in the same way as in
"rcv" callbacks, i.e. runtime errors will cause the port to get
"kil"ed.
The effect is basically as if it returned "sub { peval $SELF, sub {
BLOCK }, @_ }".
This is useful when you register callbacks from "rcv" callbacks:
rcv delayed_reply => sub {
my ($delay, @reply) = @_;
my $timer = AE::timer $delay, 0, psub {
snd @reply, $SELF;
};
};
$guard = mon $port, $rcvport # kill $rcvport when $port dies
$guard = mon $port # kill $SELF when $port dies
$guard = mon $port, $cb->(@reason) # call $cb when $port dies
$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 $port is "kil"'ed
with a non-empty reason, the other port ($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 $rvport defaults to $SELF.
The remaining forms don't distinguish between "normal" and
"abnormal" kil's - it's up to the callback or receiver to check
whether the @reason is empty and act accordingly.
In the third form (callback), the callback is simply called with any
number of @reason elements (empty @reason means that the port was
deleted "normally"). Note also that *the callback must never die*,
so use "eval" if unsure.
In the last form (message), a message of the form "$rcvport, @msg,
@reason" will be "snd".
Monitoring-actions are one-shot: once messages are lost (and a
monitoring alert was raised), they are removed and will not trigger
again, even if it turns out that the port is still alive.
As a rule of thumb, monitoring requests should always monitor a
remote port locally (using a local $rcvport or a callback). The
reason is that kill messages might get lost, just like any other
message. Another less obvious reason is that even monitoring
requests can get lost (for example, when the connection to the other
node goes down permanently). When monitoring a port locally these
problems do not exist.
"mon" effectively guarantees that, in the absence of hardware
failures, after starting the monitor, either all messages sent to
the port will arrive, or the monitoring action will be invoked after
possible message 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 $port is killed.
mon $port, sub { warn "port died because of <@_>\n" };
Example: kill ourselves when $port is killed abnormally.
mon $port;
Example: send us a restart message when another $port is killed.
mon $port, $self => "restart";
$guard = mon_guard $port, $ref, $ref...
Monitors the given $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 "psub"):
$port->rcv (start => sub {
my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
undef $timer if 0.9 < rand;
});
});
kil $port[, @reason]
Kill the specified port with the given @reason.
If no @reason is specified, then the port is killed "normally" -
monitor callback will be invoked, but the kil will not cause linked
ports ("mon $mport, $lport" form) to get killed.
If a @reason is specified, then linked ports ("mon $mport, $lport"
form) get killed with the same reason.
Runtime errors while evaluating "rcv" callbacks or inside "psub"
blocks will be reported as reason "die => $@".
Transport/communication errors are reported as "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: $!";
$port = spawn $node, $initfunc[, @initdata]
Creates a port on the node $node (which can also be a port ID, in
which case it's the node where that port resides).
The port ID of the newly created port is returned immediately, and
it is possible to immediately start sending messages or to monitor
the port.
After the port has been created, the init function is called on the
remote node, in the same context as a "rcv" callback. This function
must be a fully-qualified function name (e.g.
"MyApp::Chat::Server::init"). To specify a function in the main
program, use "::name".
If the function doesn't exist, then the node tries to "require" the
package, then the package above the package and so on (e.g.
"MyApp::Chat::Server", "MyApp::Chat", "MyApp") until the function
exists or it runs out of package names.
The init function is then called with the newly-created port as
context object ($SELF) and the @initdata values as arguments. It
*must* call one of the "rcv" functions to set callbacks on $SELF,
otherwise the port might not get created.
A common idiom is to pass a local port, immediately monitor the
spawned port, and in the remote init function, immediately monitor
the passed local port. This two-way monitoring ensures that both
ports get cleaned up when there is a problem.
( run in 1.604 second using v1.01-cache-2.11-cpan-7fcb06a456a )