cl-czmq - A re-binding of the C binding for the zmq transport layer (czmq)

Overview

cl-czmq is a lisp binding for the CZMQ C binding for the ZMQ transport layer.

ZMQ is an extremely useful socket and messaging layer which makes network programming not just possible, but fun. Read the Guide!

Why CZMQ and not ZMQ?

• Target multiple zmq versions through CZMQ.
• CZMQ is cleaner to implement. There's no need to build an arbitrary additional API on top of it - unlike zmq. This means a straight port is actually usable.
• A straight port makes it easier to translate between C and lisp for e.g. guide examples and documentation.
• CZMQ contains cool constructs such as zbeacon, zloop, zmsg, etc.
• CZMQ is in C not C++ :-)

Installation

Build zmq and czmq in your platform specific way.

We suggest using quicklisp. Install that, and then grab the cl-czmq source (via tarball or git) and put it in ~/quicklisp/local-projects/. Symlinks work okay too.

Compatibility

Tested:

• zmq 3.2.3
• czmq 1.4.1
• sbcl 1.1.7+ on Linux and Mac OSX 10.8.2
• Franz Allegro Common Lisp 8.1
  • zclock_time doesn't work due to :long-long usage. This may be 32 bit only. There's a replacement native implementation of zclock-sleep.
  • Polls don't work correctly due to the threading architecture of Franz ACL. For example, czmq's zclock_sleep always returns immediately
  • zmq_poll (and hence zpollset_poll returns immediately with ZMQ_POLLERR if you set a time greater than 0.
  • recvs and polls - even in the foreground thread - are interrupted often.

Documentation and Examples

See the czmq(7) manpage. Also see czmq.zeromq.com.

A work-in-process port of the examples in the ZMQ guide is at https://github.com/lhope/zguide/tree/master/examples/cl-czmq . Currently all examples through Chapter 3 are done. The Pirate examples of Chapter 4 are all done, too.

## Scope and Goals ##

The scope of cl-czmq is to provide CZMQ's functionality to Lisp. CZMQ provides easy functions to send and receive memory blocks, strings, message frames, and multi-part messages. It simplifies greatly the ZMQ socket options.

Some functionality of CZMQ is not ported. Fore example, Zero copy methods are pointless, since we have to copy data into C anyway.

Most cl-czmq functions are thin wrappers around CZMQ. zloop, zhash, zlist and zthread are, however, lisp re-implementations.

A minimum of extra functionality is introduced. See Using cl-czmq below.

The goal is to track a well-used API which provides solid interoperability with primitive Lisp types. Experience shows that a "Lispy" CLOS system can be beautiful to some and a hindrance to others. Others are free to layer their own API if they like.

## Using cl-czmq ##

cl-czmq is more or less a straight port of czmq. This means the CZMQ documentation straightforwardly applies. We have, however, made some changes to facilitate lisp programming style.

• Code is available in the package named :cl-czmq (nicknamed :czmq).

• Names are dashed instead of underscored. e.g. zsocket-create instead of zsocket_create.

• Constants are in lisp idiomatic style. e.g. +czmq-version-major+ instead of CZMQ_VERSION_MAJOR.

• Where a CZMQ function would return a failure signal, cl-czmq returns nil instead. e.g. NULL for a pointer or rc = -1 becomes nil.

• Where a destructor would take a reference and set the destroyed variable to NULL, we instead return the value, which would be nil if the destruction was successful.

• We have introduced a set of zpollset functions. These manipulate zmg_pollitem_t arrays for polling and zloop.

• We have included helper functions and macros to create callback functions for zloop. See zloop and polling below.

• We have included the common with- idiom for some of the classes. e.g. with-zctx, with-zsocket, etc... these take care of binding, creating and releasing the underlying blocks of memory.

polling and zloop

The one place CZMQ is lacking is that it does not provide a polling class of its own. It uses ZMQ's zmq_pollitem_t. To make up for this, we have implemented a zpollset class using the same style as CZMQ. See src/zpollset.lisp for documentation. We also provide zpollset-poll which is a direct api into zmq_poll.

zloop is a an event reactor which uses handler functions to deal with events.

Unlike the rest of cl-czmq, zloop has been ported to CL. This is so it can support full lisp closures and lisp objects. Handler functions take the zloop and triggering pollitem (or nil for timers) as the first two values, with the rest of the arguments as passed through zloop-poller and/or zloop-timer.

Dependencies

cl-czmq requires libzmq, libczmq, cffi and bordeaux-threads.

• ZMQ dependencies are available through zeromq.org.

• Lisp dependencies are available through quicklisp.

Ownership and License

cl-czmq's contributors are listed in the AUTHORS file. The authors of cl-czmq grant you use of this software under the terms of the Lisp Lesser General Public License (LLGPL). For details see the files COPYING, COPYING.LESSER and COPYING.LISP in this directory.

Contributing

If you find problems with this library please take the time to report the issue. This helps you by increasing the chance the issue will be fixed. It helps motivate me by letting me know the library is being used. It helps everyone when the fixed issue creates a stronger codebase.

To report an issue, use the cl-czmq issue tracker at github.com.

For issue fixes and improvements, we prefer github pull requests.