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.
That means that the values specified in the profile have highest
priority and the values specified directly via "configure" have
lowest priority, and can only be used to specify defaults.
If the profile specifies a node ID, then this will become the
node ID of this process. If not, then the profile name will be
used as node ID, with a unique randoms tring ("/%u") appended.
The node ID can contain some "%" sequences that are expanded: %n
is expanded to the local nodename, %u is replaced by a random
strign to make the node unique. For example, the aemp
commandline utility uses "aemp/%n/%u" as nodename, which might
expand to "aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE".
step 2, bind listener sockets
The next step is to look up the binds in the profile, followed
by binding aemp protocol listeners on all binds specified (it is
possible and valid to have no binds, meaning that the node
cannot be contacted from the outside. This means the node cannot
talk to other nodes that also have no binds, but it can still
talk to all "normal" nodes).
If the profile does not specify a binds list, then a default of
"*" is used, meaning the node will bind on a
dynamically-assigned port on every local IP address it finds.
step 3, connect to seed nodes
As the last step, the seed ID list from the profile is passed to
the AnyEvent::MP::Global module, which will then use it to keep
connectivity with at least one node at any point in time.
Example: become a distributed node using the local node name as
profile. This should be the most common form of invocation for
"daemon"-type nodes.
configure
Example: become a semi-anonymous node. This form is often used for
commandline clients.
configure nodeid => "myscript/%n/%u";
Example: configure a node using a profile called seed, which is
suitable for a seed node as it binds on all local addresses on a
fixed port (4040, customary for aemp).
# use the aemp commandline utility
# aemp profile seed binds '*:4040'
# then use it
configure profile => "seed";
# or simply use aemp from the shell again:
# aemp run profile seed
# or provide a nicer-to-remember nodeid
# aemp run profile seed nodeid "$(hostname)"
$SELF
Contains the current port id while executing "rcv" callbacks or
"psub" blocks.
*SELF, SELF, %SELF, @SELF...
Due to some quirks in how perl exports variables, it is impossible
to just export $SELF, all the symbols named "SELF" are exported by
this module, but only $SELF is currently used.
snd $port, type => @data
snd $port, @msg
Send the given message to the given port, which can identify either
a local or a remote port, and must be a port ID.
While the message can be almost anything, it is highly recommended
to use a string as first element (a port ID, or some word that
indicates a request type etc.) and to consist if only simple perl
values (scalars, arrays, hashes) - if you think you need to pass an
object, think again.
The message data logically becomes read-only after a call to this
function: modifying any argument (or values referenced by them) is
forbidden, as there can be considerable time between the call to
"snd" and the time the message is actually being serialised - in
fact, it might never be copied as within the same process it is
simply handed to the receiving port.
The type of data you can transfer depends on the transport protocol:
when JSON is used, then only strings, numbers and arrays and hashes
consisting of those are allowed (no objects). When Storable is used,
then anything that Storable can serialise and deserialise is
allowed, and for the local node, anything can be passed. Best rely
only on the common denominator of these.
$local_port = port
Create a new local port object and returns its port ID. Initially it
has no callbacks set and will throw an error when it receives
messages.
$local_port = port { my @msg = @_ }
Creates a new local port, and returns its ID. Semantically the same
as creating a port and calling "rcv $port, $callback" on it.
The block will be called for every message received on the port,
with the global variable $SELF set to the port ID. Runtime errors
will cause the port to be "kil"ed. The message will be passed as-is,
no extra argument (i.e. no port ID) will be passed to the callback.
If you want to stop/destroy the port, simply "kil" it:
my $port = port {
my @msg = @_;
...
kil $SELF;
};
rcv $local_port, $callback->(@msg)
Replaces the default callback on the specified port. There is no way
to remove the default callback: use "sub { }" to disable it, or
better "kil" the port when it is no longer needed.
The global $SELF (exported by this module) contains $port while
executing the callback. Runtime errors during callback execution
will result in the port being "kil"ed.
The default callback receives all messages not matched by a more
specific "tag" match.
rcv $local_port, tag => $callback->(@msg_without_tag), ...
Register (or replace) callbacks to be called on messages starting
with the given tag on the given port (and return the port), or
unregister it (when $callback is $undef or missing). There can only
be one callback registered for each tag.
The original message will be passed to the callback, after the first
element (the tag) has been removed. The callback will use the same
environment as the default callback (see above).
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.
"spawn" guarantees that the $initfunc has no visible effects on the
caller before "spawn" returns (by delaying invocation when spawn is
called for the local node).
Example: spawn a chat server port on $othernode.
# 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 {
...
};
}
after $timeout, @msg
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.
cal $port, @msg, $callback[, $timeout]
A simple form of RPC - sends a message to the given $port with the
given contents (@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 "kil"ed when no longer needed.
A reply message sent to the port is passed to the $callback as-is.
If an optional time-out (in seconds) is given and it is not "undef",
then the callback will be called without any arguments after the
time-out elapsed and the port is "kil"ed.
If no time-out is given (or it is "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.
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
( run in 1.455 second using v1.01-cache-2.11-cpan-39bf76dae61 )