This section explains the structure of an HPX module.
The tool create_library_skeleton.py
can be used to generate a basic skeleton. To create a library skeleton, run the
tool in the
libs subdirectory with the module name as an argument:
This creates a skeleton with the necessary files for an HPX module. It will not create any actual source files. The structure of this skeleton is as follows:
README.rst should be always included which explains the basic purpose of
the library and a link to the generated documentation.
CMakeLists.txt is created in the root directory of the module. By
default it contains a call to
add_hpx_module which takes care of most of the
boilerplate required for a module. You only need to fill in the source and
header files in most cases.
add_hpx_module requires a module name. Optional flags are:
Optional single-value arguments are:
INSTALL_BINARIES: Install the resulting library.
Optional multi-value arguments-are:
SOURCES: List of source files.
HEADERS: List of header files.
COMPAT_HEADERS: List of compatibility header files.
DEPENDENCIES: Libraries that this module depends on, such as other modules.
CMAKE_SUBDIRS: List of subdirectories to add to the module.
include directory should contain only headers that other libraries need.
For each of those headers, an automatic header test to check for self
containment will be generated. Private headers should be placed under the
src directory. This allows for clear separation. The
may include additional CMake scripts needed to generate the respective build
Compatibility headers (forwarding headers for headers whose location is changed
when creating a module, if moving them from the main library) should be placed
include_compatibility directory. This directory is not created by
Documentation is placed in the
docs folder. A empty skeleton for the index
is created, which is picked up by the main build system and will be part of the
generated documentation. Each header inside the
include directory will
automatically be processed by Doxygen and included into the documentation. If a
header should be excluded from the API reference, a comment
sphinx:undocumented needs to be added.
Tests are placed in suitable subdirectories of
When in doubt, consult existing modules for examples on how to structure the module.
Finding circular dependencies¶
Our CI will perform a check to see if there are circular dependencies between
modules. In cases where it’s not clear what is causing the circular dependency,
running the cpp-dependencies tool manually can be helpful. It can give you
detailed information on exactly which files are causing the circular dependency.
If you do not have the
cpp-dependencies tool already installed, one way of
obtaining it is by using our docker image. This way you will have exactly the
same environment as on the CI. See Using docker for development for details on how to use
the docker image.
To produce the graph produced by CI run the following command (
assumed to hold the path to the HPX source directory):
cpp-dependencies --dir $HPX_SOURCE/libs --graph-cycles circular_dependencies.dot
This will produce a
dot file in the current directory. You can inspect this
manually with a text editor. You can also convert this to an image if you have
dot circular_dependencies.dot -Tsvg -o circular_dependencies.svg
This produces an
svg file in the current directory which shows the circular
dependencies. Note that if there are no cycles the image will be empty.
You can use
cpp-dependencies to print the include paths between two modules.
cpp-dependencies --dir $HPX_SOURCE/libs --shortest <from> <to>
prints all possible paths from the module
<from> to the module
example, as most modules depend on
config, the following should give you a
long list of paths from
cpp-dependencies --dir $HPX_SOURCE/libs --shortest algorithms config
The following should report that it can’t find a path between the two modules:
cpp-dependencies --dir $HPX_SOURCE/libs --shortest config algorithms