Workspace Mechanics

This chapter defines the organization, composition, and use of Catkin workspaces. Catkin workspaces enable rapid simultaneous building and executing of numerous interdependent projects. These projects do not need to share the same build tool, but they do need to be able to either build or install to a FHS tree.

Unlike integrated development environments (IDEs) which normally only manage single projects, the purpose of Catkin is to enable the simultaneous compilation of numerous independently-authored projects.

Workspace Configuration

Most catkin commands which modify a workspace’s configuration will display the standard configuration summary, as shown below:

$ cd /tmp/path/to/my_catkin_ws
$ catkin config
--------------------------------------------------------------
Profile:                     default
Extending:                   None
Workspace:                   /tmp/path/to/my_catkin_ws
--------------------------------------------------------------
Source Space:       [exists] /tmp/path/to/my_catkin_ws/src
Log Space:         [missing] /tmp/path/to/my_catkin_ws/logs
Build Space:       [missing] /tmp/path/to/my_catkin_ws/build
Devel Space:       [missing] /tmp/path/to/my_catkin_ws/devel
Install Space:      [unused] /tmp/path/to/my_catkin_ws/install
DESTDIR:            [unused] None
--------------------------------------------------------------
Devel Space Layout:          linked
Install Space Layout:        merged
--------------------------------------------------------------
Additional CMake Args:       None
Additional Make Args:        None
Additional catkin Make Args: None
Internal Make Job Server:    True
Cache Job Environments:      False
--------------------------------------------------------------
Whitelisted Packages:        None
Blacklisted Packages:        None
--------------------------------------------------------------
Workspace configuration appears valid.
--------------------------------------------------------------

This summary describes the layout of the workspace as well as other important settings which influence build and execution behavior. Each of these options can be modified either with the config verb’s options described in the full command-line usage or by changing environment variables. The summary is composed of the following sections:

Overview Section

  • Profile – The name of this configuration.
  • Extending – Describes if your current configuration will extend another Catkin workspace, and through which mechanism it determined the location of the extended workspace:
    • No Chaining
    • Implicit Chaining – Derived from the CMAKE_PREFIX_PATH environment variable.
    • Cached Implicit Chaining – Derived from the CMAKE_PREFIX_PATH CMake cache variable.
    • Explicit Chaining – Specified by catkin config --extend
  • Workspace – The path to the workspace.
  • Source Space – The subdirectory containing the source packages.
  • Build Space – The subdirectory containing the intermediate build products for each package.
  • Devel Space – The subdirectory containing the final build products which can be used to run code, but relies on the presence of the source space.
  • Install Space – The subdirectory containing the final build products which can be used to run code, but is entirely self-contained.
  • DESTDIR – An optional prefix to the install space as defined by GNU Standards

Build Product Layout Section

  • Devel Space Layout – The organization of the devel space.
    • Linked – Write products from each package into independent isolated FHS trees, and symbolically link them into a merged FHS tree. For more details, see Linked Devel Space.
    • Merged – Write products from all packages to a single FHS tree. This is most similar to the behavior of catkin_make.
    • Isolated – Write products from each package into independent isolated FHS trees. this is most similar to the behavior of catkin_make_isolated.
  • Install Packages – Enable creating and installation into the install space.
  • Isolate Installs – Installs products into individual FHS subdirectories in the install space.

Build Tool Arguments Section

  • Additional CMake Args – Arguments to be passed to CMake during the configuration step for all packages to be built.
  • Additional Make Args – Arguments to be passed to Make during the build step for all packages to be built.
  • Additional catkin Make Args – Similar to Additional Make Args but only applies to Catkin packages.
  • Internal Make Job Server – Whether or not the internal job server should be used to coordinate parallel build jobs.
  • Cache Job Environments – Whether or not environment variables should be cached between build jobs.

Package Filter Section

  • Package Whitelist – Packages that will be built with a bare call to catkin build.
  • Package Blacklist – Packages that will not be built unless explicitly named.

Notes Section

The summary will sometimes contain notes about the workspace or the action that you’re performing, or simply tell you that the workspace configuration appears valid.

Warnings Section

If something is wrong with your configuration such as a missing source space, an additional section will appear at the bottom of the summary with details on what is wrong and how you can fix it.

Workspace Anatomy

A standard catkin workspace, as defined by REP-0128, is a directory with a prescribed set of “spaces”, each of which is contained within a directory under the workspace root. The spaces that comprise the workspace are described in the following sections. In addition to the directories specified by REP-0128, catkin_tools also adds a visible logs directory and a hidden .catkin_tools directory. The .catkin_tools directory stores persistent build configuration and profiles.

Space Default Path Contents
Source Space ./src Source code for all the packages.
Log Space ./logs Logs from building and cleaning packages.
Build Space ./build Intermediate build products for each package.
Devel Space ./devel FHS tree or trees containing all final build products.
Install Space ./install FHS tree or trees containing products of install targets.

source space

The source space contains the source code for all of the packages to be built in the workspace, as such, it is the only directory required to build a workspace. The source space is also the only directory in the catkin workspace which is not modified by any catkin command verb. No build products are written to the source space, they are all built “out-of-source” in the build space, described in the next section. You can consider the source space to be read-only.

log space

The catkin command generates a log space, called logs by default, which contains build logs for each package. Logs for each package are written in subdirectories with the same name as the package.

The latest log for each verb and stage in a given package’s log directory is also written with the format:

{VERB}.{STAGE}.log

Each previous logfile has the following format, where {INDEX} begins at 000 and increases with each execution of that verb and stage:

{VERB}.{STAGE}.{INDEX}.log

build space

Intermediate build products are written in the build space. The build space contains an isolated build directory for each package, as well as the log files which capture the output from each build stage. It is from these directories where commands like cmake and make are run.

devel space

Build products like executables, libraries, pkg-config files, and CMake config files, are generated in the devel space. The devel space is organized as an FHS tree.

Some build tools simply treat the devel space as an install prefix, but other buildtools like catkin, itself, can build targets directly into the devel space in order to skip the additional install step. For such packages, executing programs from the devel space sometimes requires that the source space is still available.

At the root of the devel space is a set of environment setup files which can be “sourced” in order to properly execute the space’s products.

install space

Finally, if the workspace is configured to install packages, the each will be installed into the install space. The install space has an FHS layout like the devel space, except it is entirely self-contained.

Additional Files Generated by catkin_tools

Configuration Directory

In addition to the standard workspace structure, catkin_tools also adds a marker directory called .catkin_tools at the root of the workspace. This directory both acts as a marker for the root of the workspace and contains persistent configuration information.

This directory contains subdirectories representing different configuration profiles, and inside of each profile directory are YAML files which contain verb-specific metadata. It additionally contains a file which lists the name of the active configuration profile if it is different from default.

Environment Setup Files

The FHS trees of the devel space and install space also contain several environment “setup” scripts. These setup scripts are intended to make it easier to use the resulting FHS tree for building other source code or for running programs built by the packages in the workspace.

The setup script can be used like this in bash:

$ source /path/to/workspace/devel/setup.bash

Or like this in zsh:

% source /path/to/workspace/devel/setup.zsh

Sourcing these setup scripts adds this workspace and any “underlaid” workspaces to your environment, prefixing several environment variables with the appropriate local workspace folders.

Environment Variable
Description
CMAKE_PREFIX_PATH
Used by CMake to find development packages,
and used by Catkin for workspace chaining.
CPATH [4]
Used by GCC to search for development headers.
LD_LIBRARY_PATH [1]
Search path for dynamically loadable libraries.
DYLD_LIBRARY_PATH [2]
Search path for dynamically loadable libraries.
PATH
Search path for executables.
PKG_CONFIG_PATH
Search path for pkg-config files.
PYTHONPATH
Search path for Python modules.
[1]GNU/Linux Only
[2]Mac OS X Only
[3]Windows Only
[4]Only in versions of catkin <= 0.7.0 (ROS Kinetic), see the changelog

The setup scripts will also execute any Catkin “env-hooks” exported by packages in the workspace. For example, this is how roslib sets the ROS_PACKAGE_PATH environment variable.

Note

Like the devel space, the install space includes setup.* and related files at the top of the file hierarchy. This is not suitable for some packaging systems, so this can be disabled by passing the -DCATKIN_BUILD_BINARY_PACKAGE="1" option to cmake using the --cmake-args option for this verb. Though this will suppress the installation of the setup files, you will loose the functionality provided by them, namely extending the environment and executing environment hooks.

Source Packages and Dependencies

A package is any folder which contains a package.xml as defined by the ROS community in ROS Enhancement Proposals REP-0127 and REP-0140.

The catkin build command builds packages in the topological order determined by the dependencies listed in the package’s package.xml file. For more information on which dependencies contribute to the build order, see the build verb documentation.

Additionally, the build_type tag is used to determine which build stages to use on the package. Supported build types are listed in Build Types. Packages without a build_type tag are assumed to be catkin packages.

For example, plain CMake packages can be built by adding a package.xml file to the root of their source tree with the build_type flag set to cmake and appropriate build_depend and run_depend tags set, as described in REP-0136. This can been done to build packages like opencv, pcl, and flann.

Workspace Chaining / Extending

An important property listed in the configuration configuration which deserves attention is the summary value of the Extending property. This affects which other collections of libraries and packages which will be visible to your workspace. This is process called “workspace chaining.”

Above, it’s mentioned that the Catkin setup files export numerous environment variables, including CMAKE_PREFIX_PATH. Since CMake 2.6.0, the CMAKE_PREFIX_PATH is used when searching for include files, binaries, or libraries using the FIND_PACKAGE(), FIND_PATH(), FIND_PROGRAM(), or FIND_LIBRARY() CMake commands.

As such, this is also the primary way that Catkin “chains” workspaces together. When you build a Catkin workspace for the first time, it will automatically use CMAKE_PREFIX_PATH to find dependencies. After that compilation, the value will be cached internally by each project as well as the Catkin setup files and they will ignore any changes to your CMAKE_PREFIX_PATH environment variable until they are cleaned.

Note

Workspace chaining is the act of putting the products of one workspace A in the search scope of another workspace B. When describing the relationship between two such chained workspaces, A and B, it is said that workspace B extends workspace A and workspace A is extended by workspace B. This concept is also sometimes referred to as “overlaying” or “inheriting” a workspace.

Similarly, when you source a Catkin workspace’s setup file from a workspace’s devel space or install space, it prepends the path containing that setup file to the CMAKE_PREFIX_PATH environment variable. The next time you initialize a workspace, it will extend the workspace that you previously sourced.

This makes it easy and automatic to chain workspaces. Previous tools like catkin_make and catkin_make_isolated had no easy mechanism for either making it obvious which workspace was being extended, nor did they provide features to explicitly extend a given workspace. This means that for users were unaware of Catkin’s use of CMAKE_PREFIX_PATH.

Since it’s not expected that 100% of users will read this section of the documentation, the catkin program adds both configuration consistency checking for the value of CMAKE_PREFIX_PATH and makes it obvious on each invocation which workspace is being extended. Furthermore, the catkin command adds an explicit extension interface to override the value of $CMAKE_PREFIX_PATH with the catkin config --extend command.

Note

While workspaces can be chained together to add search paths, invoking a build in one workspace will not cause products in any other workspace to be built.

The information about which workspace to extend can come from a few different sources, and can be classified in one of three ways:

No Chaining

This is what is shown in the above example configuration and it implies that there are no other Catkin workspaces which this workspace extends. The user has neither explicitly specified a workspace to extend, and the CMAKE_PREFIX_PATH environment variable is empty:

Extending:                   None

Implicit Chaining via CMAKE_PREFIX_PATH Environment or Cache Variable

In this case, the catkin command is implicitly assuming that you want to build this workspace against resources which have been built into the directories listed in your CMAKE_PREFIX_PATH environment variable. As such, you can control this value simply by changing this environment variable.

For example, ROS users who load their system’s installed ROS environment by calling something similar to source /opt/ros/indigo/setup.bash will normally see an Extending value such as:

Extending:             [env] /opt/ros/indigo

If you don’t want to extend the given workspace, unsetting the CMAKE_PREFIX_PATH environment variable will change it back to none. Once you have built your workspace once, this CMAKE_PREFIX_PATH will be cached by the underlying CMake buildsystem. As such, the Extending status will subsequently describe this as the “cached” extension path:

Extending:          [cached] /opt/ros/indigo

Once the extension mode is cached like this, you must use catkin clean to before changing it to something else.

Explicit Chaining via catkin config --extend

This behaves like the above implicit chaining except it means that this workspace is explicitly extending another workspace and the workspaces which the other workspace extends, recursively. This can be set with the catkin config --extend command. It will override the value of CMAKE_PREFIX_PATH and persist between builds.

Extending:        [explicit] /tmp/path/to/other_ws