Crossroads I/O core library
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Crossroads I/O ("libxs") is a library for building scalable and high performance distributed applications. It fits between classic BSD sockets, JMS/AMQP-style message queues, and enterprise message-oriented middleware.

Crossroads I/O extends the standard socket interfaces with features traditionally provided by specialised messaging middleware products, providing an abstraction of asynchronous message queues, multiple messaging patterns, message filtering (subscriptions), seamless access to multiple transport protocols, and more.

Crossroads I/O provides a native C API for applications. Support for many more languages is provided by the community through language bindings which can be found at the Crossroads website.

Building and Installation

The following instructions apply to building libxs from an official release downloaded from the Crossroads I/O website. For building directly from Git, refer to the INSTALL file included with the libxs distribution.

On POSIX platforms, libxs uses the standard autotools build system. To build and install the library, ensure your system has a C++ compiler installed, and proceed with the following steps:

  1. Run ./configure, then make to build the library.

  2. Optionally, run make check to run the built in test suite.

  3. Run make install as root.

  4. On Linux or other platforms which use for dynamic linking, run ldconfig or equivalent as root to update your system’s shared library cache.

On Windows, solution files for Visual C++ 2010 are provided in the builds/msvc/ subdirectory of the distribution.

Refer to the INSTALL file included with the libxs distribution for more detailed installation instructions.

ZeroMQ Compatibility

Crossroads I/O provides a drop-in libzmq compatibility library for ZeroMQ language bindings and applications. To enable libzmq compatibility, you must build your copy of libxs with the --enable-libzmq option to configure, or on Windows by building the appropriate solution file.

For further details refer to the doc/xs_zmq.html or the xs_zmq(7) manual page included with this distribution.

Enabling this option will overwrite any existing installation of libzmq on your system.

Reporting Bugs

To report a bug, send an email describing your problem to the Crossroads mailing list. To make sure your bug report won’t be missed, you can file a report in the bug tracker[1].

To help Crossroads developers to fix the bug, please try to provide a minimal test program, ideally written in C, that reproduces the problem you are reporting.

The bug tracker exists primarily to track bugs and pertinent data (test cases, crash logs, etc.). You should not use it for discussion. In the bug tracker your audience will be very limited. Mailing list serves the purpose of discussing bugs much better.

Contributing to the Project

Before contributing to the project make sure you understand the legal implications of doing so. These are outlined on the Crossroads I/O website[2].

To submit your contribution, send it as a patch (using git format-patch, diff, or similar) to the mailing list. Make sure to use your real name, and prefix the subject of your post with [PATCH].

All contributions will be reviewed and, if they pass review, accepted. For more details refer to the website[3].


The libxs development Git tree can be found on Github[4].

Development is coordinated on the mailing list[5]. Visit the archives[6] to join or view archives of previous discussion.

Extensive documentation is provided with the distribution. Refer to doc/xs.html, or the xs(7) manual page after you have installed libxs on your system.

Further resources, language bindings, tutorials, and more can be found on the Crossroads website[7].


Free use of this software is granted under the terms of the GNU Lesser General Public License (LGPL). For details see the files COPYING and COPYING.LESSER included with the libxs distribution.

As a special exception, the copyright holders of libxs grant you the right to link the library statically with your software. Refer to the end of the COPYING.LESSER file included with the libxs distribution for details.