LCM is a set of libraries and tools for message passing and data marshalling, targeted at real-time systems where high-bandwidth and low latency are critical. It provides a publish/subscribe message passing model and automatic marshalling/unmarshalling code generation with bindings for applications in a variety of programming languages. It was originally designed and used by the MIT DARPA Urban Challenge Team as its message passing system.

LCM is designed for tightly-coupled systems connected via a dedicated local-area network. It is not intended for message passing over the Internet. LCM has been developed for soft real-time systems: its default messaging model permits dropping messages in order to minimize the latency of new messages.

Features

• Low-latency inter-process communication
• Efficient broadcast mechanism using UDP Multicast
• Provides type-safe message marshaling that automatically detects most types of errors (such as version mismatches between different modules)
• User-friendly logging and playback
• Essentially unlimited packet size
• No centralized "database" or "hub" -- peers communicate directly
• No daemons
• Supports C, C++, Java, Python, MATLAB, and C#

Requirements

• POSIX.1-2001 system (GNU/Linux, OS X, Cygwin, Solaris, etc.) or Windows XP/Vista/7
• GLib >= 2.0

Java >= 1.5 is strongly recommended, as several important utilities distributed with LCM are written in Java.

Documentation

• LCM design overview (PDF) -- Describes the design principles of LCM, the best place to start for a quick understanding.
• More Documentation -- Tutorials, API Reference, Troubleshooting, etc.

News

Jan 20, 2012

Release 0.8.0

This release changes the C++ API, adds some features to lcm-logplayer-gui, and fixes a few bugs.

• lcm-c:
• add new macros LCM_MAJOR_VERSION, LCM_MINOR_VERSION, LCM_MICRO_VERSION to check LCM version from C/C++.
• lcm-c++:
• rename LCM::fileno() to LCM::getFileno(). fileno is implemented as a macro on some platforms, and is thus effectively a reserved keyword.
• lcm-gen:
• C++:
• don't try to dynamically resize fixed-size arrays (re  issue #42 )
• Python:
• bugfix in decoding multivariable arrays
• lcm-logplayer-gui:
• add command line parameters to:
• start logplayer with the log paused
• filter out specific channels from being played back by default.

Oct 15, 2011

Release 0.7.1

This is a bugfix and maintenance release.

• lcm-gen:
• C++:
• fix decoding of zero-length primitive arrays (re  issue #38 )
• computeHash() omit parameter name if unused
• don't #include a type's own header file for recursive types
• fix memory leak in LCM::publish() (re  issue #35 )
• inline methods for generated code
• use static local variable for getHash() to reduce liblcm dependency of generated C++ code
• #include <string> if a type has a string field
• C:
• don't #include a type's own header file for recursive types
• Java:
• add --with-jardir=DIR option to configure script to allow configuring lcm.jar destination directory.
• General:
• update lcm-gen manpage to document --c-no-pubsub
• lcm-java:
• ClassDiscoverer doesn't try to traverse unreadable files/directories

Aug 22, 2011

Release 0.7.0

This release introduces support for native C++ bindings, and includes a number of bugfixes and documentation updates.

• lcm-gen:
• Added the -x / --cpp option, which generates native C++ language bindings. See examples/cpp for examples, and the documentation for a tutorial and API reference.
• lcm-c:
• fix a minor memory leak in lcm_tcpq.c (closes  issue #33 )
• General:
• Switched documentation from GTK-Doc to Doxygen. To build most documentation, run doxygen from the docs/ directory. Java, C#, and Python API reference docs are still built separately.

June 10, 2011

Release 0.6.0

This release includes a number of bugfixes and performance enhancements

• lcm-c:
• Change internal buffering from a fixed size ringbuffer to per-subscription FIFO queues. Subscriptions start with a default maximum queue length of 30 messages, which can be adjusted using the new function

<message_type>_subscription_set_queue_capacity()

For example, to set the queue size to 5 for a message type example_t:

       example_t_subscription_t* subs =
           example_t_subscribe(lcm, "EXAMPLE", message_handler);
       example_t_subscription_set_queue_capacity(subs, 5);

• Explicitly disallow recursive calls to lcm_handle.
• fix synchronization issues when allocating receive resources and conducting multicast self-test. see  issue #30 
• lcm-logplayer-gui:
• expose remote log player play and pause commands
• lcm-logger:
• bugfix when creating subdirectories for output files
• lcm-spy:
• bugfix when LCM URLs contain equal signs
• searches directories on classpath for lcmtype .class files, in addition to .jar files.
• lcm-gen:
• Python
• bugfix. remove extraneous typename
• Constructor initializes valid fixed-size arrays
• initialize float, double to 0.0 instead of 0
• Java
• now appends 'f' for const float
• General:
• flush stdout before failing on parse / semantic error
• General:
• add example for using LCM with GLib event loop
• add example program for using LCM with select()
• minor updates to API documentation

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