man ZeroMQ::Socket (3): A 0MQ Socket object

SYNOPSIS

use ZeroMQ qw/:all/;

my $cxt = ZeroMQ::Context->new;
my $sock = ZeroMQ::Socket->new($cxt, ZMQ_REP);

DESCRIPTION

0MQ sockets present an abstraction of a asynchronous message queue, with the exact queueing semantics depending on the socket type in use.

Key differences to conventional sockets

Quoting the 0MQ manual:

Generally speaking, conventional sockets present a synchronous interface to either connection-oriented reliable byte streams ("SOCK_STREAM"), or connection-less unreliable datagrams ("SOCK_DGRAM"). In comparison, 0MQ sockets present an abstraction of an asynchronous message queue, with the exact queueing semantics depending on the socket type in use. Where conventional sockets transfer streams of bytes or discrete datagrams, 0MQ sockets transfer discrete messages.

0MQ sockets being asynchronous means that the timings of the physical connection setup and teardown, reconnect and effective delivery are transparent to the user and organized by 0MQ itself. Further, messages may be queued in the event that a peer is unavailable to receive them.

Conventional sockets allow only strict one-to-one (two peers), many-to-one (many clients, one server), or in some cases one-to-many (multicast) relationships. With the exception of "ZMQ_PAIR", 0MQ sockets may be connected to multiple endpoints using c<connect()>, while simultaneously accepting incoming connections from multiple endpoints bound to the socket using c<bind()>, thus allowing many-to-many relationships.

Socket types

For detailed explanations of the socket types, check the official 0MQ documentation. This is just a short list of types:

Request-reply pattern: The "ZMQ_REQ" type is for the client that sends, then receives. The "ZMQ_REP" type is for the server that receives a message, then answers.
Publish-subscribe pattern: The "ZMQ_PUB" type is for publishing messages to an arbitrary number of subscribers only. The "ZMQ_SUB" type is for subscribers that receive messages.
Pipeline pattern: The "ZMQ_UPSTREAM" socket type sends messages in a pipeline pattern. "ZMQ_DOWNSTREAM" receives them.
Exclusive pair pattern: The "ZMQ_PAIR" type allows bidirectional message passing between two participants.

METHODS

new

Creates a new "ZeroMQ::Socket".

First argument must be the ZeroMQ::Context in which the socket is to live. Second argument is the socket type.

The newly created socket is initially unbound, and not associated with any endpoints. In order to establish a message flow a socket must first be connected to at least one endpoint with the "connect" method or at least one endpoint must be created for accepting incoming connections with the "bind" method.

bind

The "bind($endpoint)" method function creates an endpoint for accepting connections and binds it to the socket.

Quoting the 0MQ manual: The endpoint argument is a string consisting of two parts as follows: "transport://address". The transport part specifies the underlying transport protocol to use. The meaning of the address part is specific to the underlying transport protocol selected.

The following transports are defined. Refer to the 0MQ manual for details.

inproc: Local in-process (inter-thread) communication transport.
ipc: Local inter-process communication transport.
tcp: Unicast transport using TCP.
pgm, epgm: Reliable multicast transport using PGM.

With the exception of "ZMQ_PAIR" sockets, a single socket may be connected to multiple endpoints using "connect($endpoint)", while simultaneously accepting incoming connections from multiple endpoints bound to the socket using "bind($endpoint")>. The exact semantics depend on the socket type.

connect

Connect to an existing endpoint. Takes an enpoint string as argument, see the documentation for "bind($endpoint)" above.

close

send

The "send($msg, $flags)" method queues the given message to be sent to the socket. The flags argument is a combination of the flags defined below.

send_as( $type, $message, $flags )

ZMQ_NOBLOCK: Specifies that the operation should be performed in non-blocking mode. If the message cannot be queued on the socket, the "send()" method fails with errno set to EAGAIN.
ZMQ_SNDMORE: Specifies that the message being sent is a multi-part message, and that further message parts are to follow. Refer to the 0MQ manual for details regarding multi-part messages.

recv

The "my $msg = $sock->recv($flags)" method receives a message from the socket and returns it as a new "ZeroMQ::Message" object. If there are no messages available on the specified socket the "recv()" method blocks until the request can be satisfied. The flags argument is a combination of the flags defined below.

recv_as( $type, $flags )

ZMQ_NOBLOCK: Specifies that the operation should be performed in non-blocking mode. If there are no messages available on the specified socket, the "$sock->recv(ZMQ_NOBLOCK)" method call returns "undef" and sets $ERRNO to "EAGAIN".

getsockopt

The "my $optval = $sock->getsockopt(ZMQ_SOME_OPTION)" method call retrieves the value for the given socket option.

The following options can be retrieved. For a full explanation of the options, please refer to the 0MQ manual.

ZMQ_RCVMORE: More message parts to follow
ZMQ_HWM: Retrieve high water mark
ZMQ_SWAP: Retrieve disk offload size
ZMQ_AFFINITY: Retrieve I/O thread affinity
ZMQ_IDENTITY: Retrieve socket identity
ZMQ_RATE: Retrieve multicast data rate
ZMQ_RECOVERY_IVL: Get multicast recovery interval
ZMQ_MCAST_LOOP: Control multicast loopback
ZMQ_SNDBUF: Retrieve kernel transmit buffer size
ZMQ_RCVBUF: Retrieve kernel receive buffer size

setsockopt

The "$sock->setsockopt(ZMQ_SOME_OPTION, $value)" method call sets the specified option to the given value.

The following socket options can be set. For details, please refer to the 0MQ manual:

ZMQ_HWM: Set high water mark
ZMQ_SWAP: Set disk offload size
ZMQ_AFFINITY: Set I/O thread affinity
ZMQ_IDENTITY: Set socket identity
ZMQ_SUBSCRIBE: Establish message filter
ZMQ_UNSUBSCRIBE: Remove message filter
ZMQ_RATE: Set multicast data rate
ZMQ_RECOVERY_IVL: Set multicast recovery interval
ZMQ_MCAST_LOOP: Control multicast loopback
ZMQ_SNDBUF: Set kernel transmit buffer size
ZMQ_RCVBUF: Set kernel receive buffer size

CAVEATS

"ZeroMQ::Socket" objects aren't thread safe due to the underlying library. Therefore, they are currently not cloned when a new Perl ithread is spawned. The variables in the new thread that contained the socket in the parent thread will be a scalar reference to "undef" in the new thread. This makes the Perl wrapper thread safe (i.e. no segmentation faults).

AUTHOR

Daisuke Maki <[email protected]>

Steffen Mueller, <[email protected]>

COPYRIGHT AND LICENSE

The ZeroMQ module is

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.0 or, at your option, any later version of Perl 5 you may have available.