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Dylan Cali

NAME

ZMQ::FFI - version agnostic Perl bindings for zeromq using ffi

VERSION

version 1.06

SYNOPSIS

    #### send/recv ####

    use v5.10;
    use ZMQ::FFI;
    use ZMQ::FFI::Constants qw(ZMQ_REQ ZMQ_REP);

    my $endpoint = "ipc://zmq-ffi-$$";
    my $ctx      = ZMQ::FFI->new();

    my $s1 = $ctx->socket(ZMQ_REQ);
    $s1->connect($endpoint);

    my $s2 = $ctx->socket(ZMQ_REP);
    $s2->bind($endpoint);

    $s1->send('ohhai');

    say $s2->recv();
    # ohhai


    #### pub/sub ####

    use v5.10;
    use ZMQ::FFI;
    use ZMQ::FFI::Constants qw(ZMQ_PUB ZMQ_SUB);
    use Time::HiRes q(usleep);

    my $endpoint = "ipc://zmq-ffi-$$";
    my $ctx      = ZMQ::FFI->new();

    my $s = $ctx->socket(ZMQ_SUB);
    my $p = $ctx->socket(ZMQ_PUB);

    $s->connect($endpoint);
    $p->bind($endpoint);

    # all topics
    {
        $s->subscribe('');

        until ($s->has_pollin) {
            # compensate for slow subscriber
            usleep 100_000;
            $p->send('ohhai');
        }

        say $s->recv();
        # ohhai

        $s->unsubscribe('');
    }

    # specific topics
    {
        $s->subscribe('topic1');
        $s->subscribe('topic2');

        until ($s->has_pollin) {
            usleep 100_000;
            $p->send('topic1 ohhai');
            $p->send('topic2 ohhai');
        }

        while ($s->has_pollin) {
            say join ' ', $s->recv();
            # topic1 ohhai
            # topic2 ohhai
        }
    }


    #### multipart ####

    use v5.10;
    use ZMQ::FFI;
    use ZMQ::FFI::Constants qw(ZMQ_DEALER ZMQ_ROUTER);

    my $endpoint = "ipc://zmq-ffi-$$";
    my $ctx      = ZMQ::FFI->new();

    my $d = $ctx->socket(ZMQ_DEALER);
    $d->set_identity('dealer');

    my $r = $ctx->socket(ZMQ_ROUTER);

    $d->connect($endpoint);
    $r->bind($endpoint);

    $d->send_multipart([qw(ABC DEF GHI)]);

    say join ' ', $r->recv_multipart;
    # dealer ABC DEF GHI


    #### nonblocking ####

    use v5.10;
    use ZMQ::FFI;
    use ZMQ::FFI::Constants qw(ZMQ_PUSH ZMQ_PULL);
    use AnyEvent;
    use EV;

    my $endpoint = "ipc://zmq-ffi-$$";
    my $ctx      = ZMQ::FFI->new();
    my @messages = qw(foo bar baz);


    my $pull = $ctx->socket(ZMQ_PULL);
    $pull->bind($endpoint);

    my $fd = $pull->get_fd();

    my $recv = 0;
    my $w = AE::io $fd, 0, sub {
        while ( $pull->has_pollin ) {
            say $pull->recv();
            # foo, bar, baz

            $recv++;
            if ($recv == 3) {
                EV::break();
            }
        }
    };


    my $push = $ctx->socket(ZMQ_PUSH);
    $push->connect($endpoint);

    my $sent = 0;
    my $t;
    $t = AE::timer 0, .1, sub {
        $push->send($messages[$sent]);

        $sent++;
        if ($sent == 3) {
            undef $t;
        }
    };

    EV::run();


    #### specifying versions ####

    use ZMQ::FFI;

    # 2.x context
    my $ctx = ZMQ::FFI->new( soname => 'libzmq.so.1' );
    my ($major, $minor, $patch) = $ctx->version;

    # 3.x context
    my $ctx = ZMQ::FFI->new( soname => 'libzmq.so.3' );
    my ($major, $minor, $patch) = $ctx->version;

DESCRIPTION

ZMQ::FFI exposes a high level, transparent, OO interface to zeromq independent of the underlying libzmq version. Where semantics differ, it will dispatch to the appropriate backend for you. As it uses ffi, there is no dependency on XS or compilation.

As of 1.00 ZMQ::FFI is implemented using FFI::Platypus. This version has substantial performance improvements and you are encouraged to use 1.00 or newer.

CONTEXT API

new

    my $ctx = ZMQ::FFI->new(%options);

returns a new context object, appropriate for the version of libzmq found on your system. It accepts the following optional attributes:

options

threads

zeromq thread pool size. Default: 1

max_sockets

requires zmq >= 3.x

max number of sockets allowed for context. Default: 1024

soname
    ZMQ::FFI->new( soname => '/path/to/libzmq.so' );
    ZMQ::FFI->new( soname => 'libzmq.so.3' );

specify the libzmq library name to load. By default ZMQ::FFI will first try the generic soname for the system, then the soname for each version of zeromq (e.g. libzmq.so.3). soname can also be the path to a particular libzmq so file

It is technically possible to have multiple contexts of different versions in the same process, though the utility of doing such a thing is dubious

version

    my ($major, $minor, $patch) = $ctx->version();

return the libzmq version as the list ($major, $minor, $patch)

get

requires zmq >= 3.x

    my $threads = $ctx->get(ZMQ_IO_THREADS)

get a context option value

set

requires zmq >= 3.x

    $ctx->set(ZMQ_MAX_SOCKETS, 42)

set a context option value

socket

    my $socket = $ctx->socket(ZMQ_REQ)

returns a socket of the specified type. See "SOCKET API" below

proxy

    $ctx->proxy($frontend, $backend);

    $ctx->proxy($frontend, $backend, $capture);

sets up and runs a zmq_proxy. For zmq 2.x this will use a ZMQ_STREAMER device to simulate the proxy. The optional $capture is only supported for zmq >= 3.x however

device

zmq 2.x only

    $ctx->device($type, $frontend, $backend);

sets up and runs a zmq_device with specified frontend and backend sockets

destroy

destroy the underlying zmq context. In general you shouldn't have to call this directly as it is called automatically for you when the object gets reaped

See "CLEANUP" below

SOCKET API

The following API is available on socket objects created by $ctx->socket.

For core attributes and functions, common across all versions of zeromq, convenience methods are provided. Otherwise, generic get/set methods are provided that will work independent of version.

As attributes are constantly being added/removed from zeromq, it is unlikely the 'static' accessors will grow much beyond the current set.

version

    my ($major, $minor, $patch) = $socket->version();

same as Context version above

connect

    $socket->connect($endpoint);

does socket connect on the specified endpoint

disconnect

requires zmq >= 3.x

    $socket->disconnect($endpoint);

does socket disconnect on the specified endpoint

bind

    $socket->bind($endpoint);

does socket bind on the specified endpoint

unbind

requires zmq >= 3.x

    $socket->unbind($endpoint);

does socket unbind on the specified endpoint

get_linger, set_linger

    my $linger = $socket->get_linger();

    $socket->set_linger($millis);

get or set the socket linger period. Default: 0 (no linger)

See "CLEANUP" below

get_identity, set_identity

    my $ident = $socket->get_identity();

    $socket->set_identity($ident);

get or set the socket identity for request/reply patterns

get_fd

    my $fd = $socket->get_fd();

get the file descriptor associated with the socket

get

    my $linger = $socket->get(ZMQ_LINGER, 'int');

return the value for the specified socket option. $option_type is the type associated with the option value in the zeromq API (zmq_getsockopt man page)

set

    $socket->set(ZMQ_IDENTITY, 'binary', 'foo');

set the socket option to the specified value. $option_type is the type associated with the option value in the zeromq API (zmq_setsockopt man page)

subscribe

    $socket->subscribe($topic);

add $topic to the subscription list

unsubscribe

    $socket->unsubscribe($topic);

remove $topic from the subscription list

send

    $socket->send($msg);

    $socket->send($msg, $flags);

sends a message using the optional flags

send_multipart

    $socket->send($parts_aref);

    $socket->send($parts_aref, $flags);

given an array ref of message parts, sends the multipart message using the optional flags. ZMQ_SNDMORE semantics are handled for you

recv

    my $msg = $socket->recv();

    my $msg = $socket->recv($flags);

receives a message using the optional flags

recv_multipart

    my @parts = $socket->recv_multipart();

    my @parts = $socket->recv_multipart($flags);

receives a multipart message, returning an array of parts. ZMQ_RCVMORE semantics are handled for you

has_pollin, has_pollout

    while ( $socket->has_pollin ) { ... }

checks ZMQ_EVENTS for ZMQ_POLLIN and ZMQ_POLLOUT respectively, and returns true/false depending on the state

close

close the underlying zmq socket. In general you shouldn't have to call this directly as it is called automatically for you when the object gets reaped

See "CLEANUP" below

die_on_error

    $socket->die_on_error(0);

    $socket->die_on_error(1);

controls whether error handling should be exceptional or not. This is set to true by default. See "ERROR HANDLING" below

has_error

returns true or false depending on whether the last socket operation had an error. This is really just an alias for last_errno

last_errno

returns the system errno set by the last socket operation, or 0 if there was no error

last_strerror

returns the human readable system error message associated with the socket last_errno

CLEANUP

With respect to cleanup ZMQ::FFI follows either the zeromq guide recommendations or the behavior of other zmq bindings. That is:

  • it uses 0 linger by default (this is the default used by czmq and jzmq)

  • during object destruction it will call close/destroy for you

  • it arranges the reference hierarchy such that sockets will be properly cleaned up before their associated contexts

  • it detects fork/thread situations and ensures sockets/contexts are only cleaned up in their originating process/thread

  • it guards against double closes/destroys

Given the above you're probably better off letting ZMQ::FFI handle cleanup for you. But if for some reason you want to do explicit cleanup yourself you can. All the below will accomplish the same thing:

    # implicit cleanup
    {
        my $context = ZMQ::FFI->new();
        my $socket  = $ctx->socket($type);
        ...
        # close/destroy called in destructors at end of scope
    }

    # explicit cleanup
    $socket->close();
    $context->destroy();

    # ditto
    undef $socket;
    undef $context;

Regarding linger, you can always set this to a value you prefer if you don't like the default. Once set the new value will be used when the socket is subsequently closed (either implicitly or explicitly):

    $socket->set_linger(-1); # infinite linger
                             # $context->destroy will block forever
                             # (or until all pending messages have been sent)

ERROR HANDLING

By default, ZMQ::FFI checks the return codes of underlying zmq functions for you, and in the case of an error it will die with the human readable system error message.

    $ctx->socket(-1);
    # dies with 'zmq_socket: Invalid argument'

Usually this is what you want, but not always. Some zmq operations can return errors that are not fatal and should be handled. For example using ZMQ_DONTWAIT with send/recv can return EAGAIN and simply means try again, not die.

For situations such as this you can turn off exceptional error handling by setting die_on_error to 0. It is then for you to check and manage any zmq errors by checking last_errno:

    use Errno qw(EAGAIN);

    my $ctx = ZMQ::FFI->new();
    my $s   = $ctx->socket(ZMQ_DEALER);
    $s->bind('tcp://*:7200');

    $s->die_on_error(0); # turn off exceptional error handling

    while (1) {
        my $msg = $s->recv(ZMQ_DONTWAIT);

        if ($s->last_errno == EAGAIN) {
            sleep 1;
        }
        elsif ($s->last_errno) {
            die $s->last_strerror;
        }
        else {
            warn "recvd: $msg";
            last;
        }
    }

    $s->die_on_error(1); # turn back on exceptional error handling

FFI VS XS PERFORMANCE

ZMQ::FFI uses FFI::Platypus on the backend. In addition to a friendly, usable interface, FFI::Platypus's killer feature is attach. attach makes it possible to bind ffi functions in memory as first class Perl xsubs. This results in dramatic performance gains and gives you the flexibility of ffi with performance approaching that of XS.

Testing indicates FFI::Platypus xsubs are around 30% slower than "real" XS xsubs. That may sound like a lot, but to put it in perspective that means, for zeromq, the XS bindings can send 10 million messages 1-2 seconds faster than the ffi ones.

If you really care about 1-2 seconds over 10 million messages you should be writing your solution in C anyways. An equivalent C implementation will be several hundred percent faster or more.

Keep in mind also that the small speed bump you get using XS can easily be wiped out by crappy and poorly optimized Perl code.

Now that Perl finally has a great ffi interface, it is hard to make the case to continue using XS. The slight speed bump just isn't worth giving up the convenience, flexibility, and portability of ffi.

You can find the detailed performance results that informed this section at: https://gist.github.com/calid/17df5bcfb81c83786d6f

BUGS

ZMQ::FFI is free as in beer in addition to being free as in speech. While I've done my best to ensure it's tasty, high quality beer, it probably isn't perfect. If you encounter problems, or otherwise see room for improvement, please open an issue (or even better a pull request!) on github

SEE ALSO

AUTHOR

Dylan Cali <calid1984@gmail.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by Dylan Cali.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.