Creating HPX projects¶

Using HPX with pkg-config¶

How to build HPX applications with pkg-config¶

After you are done installing HPX, you should be able to build the following program. It prints Hello World! on the locality you run it on.

// Including 'hpx/hpx_main.hpp' instead of the usual 'hpx/hpx_init.hpp' enables
// to use the plain C-main below as the direct main HPX entry point.
#include <hpx/hpx_main.hpp>
#include <hpx/iostream.hpp>

int main()
{
    // Say hello to the world!
    hpx::cout << "Hello World!\n" << hpx::flush;
    return 0;
}

Copy the text of this program into a file called hello_world.cpp.

Now, in the directory where you put hello_world.cpp, issue the following commands (where $HPX_LOCATION is the build directory or CMAKE_INSTALL_PREFIX you used while building HPX):

export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:$HPX_LOCATION/lib/pkgconfig
c++ -o hello_world hello_world.cpp \
   `pkg-config --cflags --libs hpx_application`\
    -lhpx_iostreams -DHPX_APPLICATION_NAME=hello_world

Important

When using pkg-config with HPX, the pkg-config flags must go after the -o flag.

Note

HPX libraries have different names in debug and release mode. If you want to link against a debug HPX library, you need to use the _debug suffix for the pkg-config name. That means instead of hpx_application or hpx_component, you will have to use hpx_application_debug or hpx_component_debug Moreover, all referenced HPX components need to have an appended d suffix. For example, instead of -lhpx_iostreams you will need to specify -lhpx_iostreamsd.

Important

If the HPX libraries are in a path that is not found by the dynamic linker, you will need to add the path $HPX_LOCATION/lib to your linker search path (for example LD_LIBRARY_PATH on Linux).

To test the program, type:

./hello_world

which should print Hello World! and exit.

How to build HPX components with pkg-config¶

Let’s try a more complex example involving an HPX component. An HPX component is a class that exposes HPX actions. HPX components are compiled into dynamically loaded modules called component libraries. Here’s the source code:

hello_world_component.cpp

#include <hpx/config.hpp>
#if !defined(HPX_COMPUTE_DEVICE_CODE)
#include "hello_world_component.hpp"
#include <hpx/iostream.hpp>

#include <iostream>

namespace examples { namespace server
{
    void hello_world::invoke()
    {
        hpx::cout << "Hello HPX World!" << std::endl;
    }
}}

HPX_REGISTER_COMPONENT_MODULE();

typedef hpx::components::component<
    examples::server::hello_world
> hello_world_type;

HPX_REGISTER_COMPONENT(hello_world_type, hello_world);

HPX_REGISTER_ACTION(
    examples::server::hello_world::invoke_action, hello_world_invoke_action);
#endif

hello_world_component.hpp

#pragma once

#include <hpx/config.hpp>
#if !defined(HPX_COMPUTE_DEVICE_CODE)
#include <hpx/hpx.hpp>
#include <hpx/include/actions.hpp>
#include <hpx/include/lcos.hpp>
#include <hpx/include/components.hpp>
#include <hpx/serialization.hpp>

#include <utility>

namespace examples { namespace server
{
    struct HPX_COMPONENT_EXPORT hello_world
        : hpx::components::component_base<hello_world>
    {
        void invoke();
        HPX_DEFINE_COMPONENT_ACTION(hello_world, invoke);
    };
}}

HPX_REGISTER_ACTION_DECLARATION(
    examples::server::hello_world::invoke_action, hello_world_invoke_action);

namespace examples
{
    struct hello_world
      : hpx::components::client_base<hello_world, server::hello_world>
    {
        typedef hpx::components::client_base<hello_world, server::hello_world>
            base_type;

        hello_world(hpx::future<hpx::naming::id_type> && f)
          : base_type(std::move(f))
        {}

        hello_world(hpx::naming::id_type && f)
          : base_type(std::move(f))
        {}

        void invoke()
        {
            hpx::async<server::hello_world::invoke_action>(this->get_id()).get();
        }
    };
}

#endif

hello_world_client.cpp

#include <hpx/config.hpp>
#if defined(HPX_COMPUTE_HOST_CODE)
#include <hpx/wrap_main.hpp>

#include "hello_world_component.hpp"

int main()
{
    {
        // Create a single instance of the component on this locality.
        examples::hello_world client =
            hpx::new_<examples::hello_world>(hpx::find_here());

        // Invoke the component's action, which will print "Hello World!".
        client.invoke();
    }

    return 0;
}
#endif

Copy the three source files above into three files (called hello_world_component.cpp, hello_world_component.hpp and hello_world_client.cpp, respectively).

Now, in the directory where you put the files, run the following command to build the component library. (where $HPX_LOCATION is the build directory or CMAKE_INSTALL_PREFIX you used while building HPX):

export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:$HPX_LOCATION/lib/pkgconfig
c++ -o libhpx_hello_world.so hello_world_component.cpp \
   `pkg-config --cflags --libs hpx_component` \
    -lhpx_iostreams -DHPX_COMPONENT_NAME=hpx_hello_world

Now pick a directory in which to install your HPX component libraries. For this example, we’ll choose a directory named my_hpx_libs:

mkdir ~/my_hpx_libs
mv libhpx_hello_world.so ~/my_hpx_libs

Note

HPX libraries have different names in debug and release mode. If you want to link against a debug HPX library, you need to use the _debug suffix for the pkg-config name. That means instead of hpx_application or hpx_component you will have to use hpx_application_debug or hpx_component_debug. Moreover, all referenced HPX components need to have a appended d suffix, e.g. instead of -lhpx_iostreams you will need to specify -lhpx_iostreamsd.

Important

If the HPX libraries are in a path that is not found by the dynamic linker. You need to add the path $HPX_LOCATION/lib to your linker search path (for example LD_LIBRARY_PATH on Linux).

Now, to build the application that uses this component (hello_world_client.cpp), we do:

export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:$HPX_LOCATION/lib/pkgconfig
c++ -o hello_world_client hello_world_client.cpp \
   ``pkg-config --cflags --libs hpx_application``\
    -L${HOME}/my_hpx_libs -lhpx_hello_world -lhpx_iostreams

Important

When using pkg-config with HPX, the pkg-config flags must go after the -o flag.

Finally, you’ll need to set your LD_LIBRARY_PATH before you can run the program. To run the program, type:

export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$HOME/my_hpx_libs"
./hello_world_client

which should print Hello HPX World! and exit.

Using HPX with CMake-based projects¶

In addition to the pkg-config support discussed on the previous pages, HPX comes with full CMake support. In order to integrate HPX into existing or new CMakeLists.txt, you can leverage the find_package command integrated into CMake. Following, is a Hello World component example using CMake.

Let’s revisit what we have. We have three files that compose our example application:

hello_world_component.hpp
hello_world_component.cpp
hello_world_client.hpp

The basic structure to include HPX into your CMakeLists.txt is shown here:

# Require a recent version of cmake
cmake_minimum_required(VERSION 3.17 FATAL_ERROR)

# This project is C++ based.
project(your_app CXX)

# Instruct cmake to find the HPX settings
find_package(HPX)

In order to have CMake find HPX, it needs to be told where to look for the HPXConfig.cmake file that is generated when HPX is built or installed. It is used by find_package(HPX) to set up all the necessary macros needed to use HPX in your project. The ways to achieve this are:

Set the HPX_DIR CMake variable to point to the directory containing the HPXConfig.cmake script on the command line when you invoke CMake:
```
cmake -DHPX_DIR=$HPX_LOCATION/lib/cmake/HPX ...
```
where $HPX_LOCATION is the build directory or CMAKE_INSTALL_PREFIX you used when building/configuring HPX.
Set the CMAKE_PREFIX_PATH variable to the root directory of your HPX build or install location on the command line when you invoke CMake:
```
cmake -DCMAKE_PREFIX_PATH=$HPX_LOCATION ...
```
The difference between CMAKE_PREFIX_PATH and HPX_DIR is that CMake will add common postfixes, such as lib/cmake/<project, to the CMAKE_PREFIX_PATH and search in these locations too. Note that if your project uses HPX as well as other CMake-managed projects, the paths to the locations of these multiple projects may be concatenated in the CMAKE_PREFIX_PATH.
The variables above may be set in the CMake GUI or curses ccmake interface instead of the command line.

Additionally, if you wish to require HPX for your project, replace the find_package(HPX) line with find_package(HPX REQUIRED).

You can check if HPX was successfully found with the HPX_FOUND CMake variable.

Using CMake targets¶

The recommended way of setting up your targets to use HPX is to link to the HPX::hpx CMake target:

target_link_libraries(hello_world_component PUBLIC HPX::hpx)

This requires that you have already created the target like this:

add_library(hello_world_component SHARED hello_world_component.cpp)
target_include_directories(hello_world_component PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

When you link your library to the HPX::hpx CMake target, you will be able use HPX functionality in your library. To use main() as the implicit entry point in your application you must additionally link your application to the CMake target HPX::wrap_main. This target is automatically linked to executables if you are using the macros described below (Using macros to create new targets). See Re-use the main() function as the main HPX entry point for more information on implicitly using main() as the entry point.

Creating a component requires setting two additional compile definitions:

target_compile_options(hello_world_component
  HPX_COMPONENT_NAME=hello_world
  HPX_COMPONENT_EXPORTS)

Instead of setting these definitions manually you may link to the HPX::component target, which sets HPX_COMPONENT_NAME to hpx_<target_name>, where <target_name> is the target name of your library. Note that these definitions should be PRIVATE to make sure these definitions are not propagated transitively to dependent targets.

In addition to making your library a component you can make it a plugin. To do so link to the HPX::plugin target. Similarly to HPX::component this will set HPX_PLUGIN_NAME to hpx_<target_name>. This definition should also be PRIVATE. Unlike regular shared libraries, plugins are loaded at runtime from certain directories and will not be found without additional configuration. Plugins should be installed into a directory containing only plugins. For example, the plugins created by HPX itself are installed into the hpx subdirectory in the library install directory (typically lib or lib64). When using the HPX::plugin target you need to install your plugins into an appropriate directory. You may also want to set the location of your plugin in the build directory with the *_OUTPUT_DIRECTORY* CMake target properties to be able to load the plugins in the build directory. Once you’ve set the install or output directory of your plugin you need to tell your executable where to find it at runtime. You can do this either by setting the environment variable HPX_COMPONENT_PATHS or the ini setting hpx.component_paths (see --hpx:ini) to the directory containing your plugin.

Using macros to create new targets¶

In addition to the targets described above, HPX provides convenience macros to hide optional boilerplate code that may be useful for your project. The link to the targets described above. We recommend that you use the targets directly whenever possible as they tend to compose better with other targets.

The macro for adding an HPX component is add_hpx_component. It can be used in your CMakeLists.txt file like this:

# build your application using HPX
add_hpx_component(hello_world
    SOURCES hello_world_component.cpp
    HEADERS hello_world_component.hpp
    COMPONENT_DEPENDENCIES iostreams)

Note

add_hpx_component adds a _component suffix to the target name. In the example above, a hello_world_component target will be created.

The available options to add_hpx_component are:

SOURCES: The source files for that component
HEADERS: The header files for that component
DEPENDENCIES: Other libraries or targets this component depends on
COMPONENT_DEPENDENCIES: The components this component depends on
PLUGIN: Treats this component as a plugin-able library
COMPILE_FLAGS: Additional compiler flags
LINK_FLAGS: Additional linker flags
FOLDER: Adds the headers and source files to this Source Group folder

EXCLUDE_FROM_ALL: Do not build this component as part of the all target

After adding the component, the way you add the executable is as follows:

# build your application using HPX
add_hpx_executable(hello_world
    SOURCES hello_world_client.cpp
    COMPONENT_DEPENDENCIES hello_world)

Note

add_hpx_executable automatically adds a _component suffix to dependencies specified in COMPONENT_DEPENDENCIES, meaning you can directly use the name given when adding a component using add_hpx_component.

When you configure your application, all you need to do is set the HPX_DIR variable to point to the installation of HPX.

Note

All library targets built with HPX are exported and readily available to be used as arguments to target_link_libraries in your targets. The HPX include directories are available with the HPX_INCLUDE_DIRS CMake variable.

Using the HPX compiler wrapper `hpxcxx`¶

The hpxcxx compiler wrapper helps to compile a HPX component, application, or object file, based on the arguments passed to it.

hpxcxx [--exe=<APPLICATION_NAME> | --comp=<COMPONENT_NAME> | -c] FLAGS FILES

The hpxcxx command requires that either an application or a component is built or -c flag is specified. If the build is against a debug build, the -g is to be specified while building.

Optional `FLAGS`¶

-l <LIBRARY> | -l<LIBRARY>: Links <LIBRARY> to the build
-g: Specifies that the application or component build is against a debug build
-rd: Sets release-with-debug-info option
-mr: Sets minsize-release option

All other flags (like -o OUTPUT_FILE) are directly passed to the underlying C++ compiler.

Using macros to set up existing targets to use HPX¶

In addition to the add_hpx_component and add_hpx_executable, you can use the hpx_setup_target macro to have an already existing target to be used with the HPX libraries:

hpx_setup_target(target)

Optional parameters are:

EXPORT: Adds it to the CMake export list HPXTargets
INSTALL: Generates an install rule for the target
PLUGIN: Treats this component as a plugin-able library
TYPE: The type can be: EXECUTABLE, LIBRARY or COMPONENT
DEPENDENCIES: Other libraries or targets this component depends on
COMPONENT_DEPENDENCIES: The components this component depends on
COMPILE_FLAGS: Additional compiler flags
LINK_FLAGS: Additional linker flags

If you do not use CMake, you can still build against HPX, but you should refer to the section on How to build HPX components with pkg-config.

Note

Since HPX relies on dynamic libraries, the dynamic linker needs to know where to look for them. If HPX isn’t installed into a path that is configured as a linker search path, external projects need to either set RPATH or adapt LD_LIBRARY_PATH to point to where the HPX libraries reside. In order to set RPATHs, you can include HPX_SetFullRPATH in your project after all libraries you want to link against have been added. Please also consult the CMake documentation here.

Using HPX with Makefile¶

A basic project building with HPX is through creating makefiles. The process of creating one can get complex depending upon the use of cmake parameter HPX_WITH_HPX_MAIN (which defaults to ON).

How to build HPX applications with makefile¶

If HPX is installed correctly, you should be able to build and run a simple Hello World program. It prints Hello World! on the locality you run it on.

// Including 'hpx/hpx_main.hpp' instead of the usual 'hpx/hpx_init.hpp' enables
// to use the plain C-main below as the direct main HPX entry point.
#include <hpx/hpx_main.hpp>
#include <hpx/iostream.hpp>

int main()
{
    // Say hello to the world!
    hpx::cout << "Hello World!\n" << hpx::flush;
    return 0;
}

Copy the content of this program into a file called hello_world.cpp.

Now, in the directory where you put hello_world.cpp, create a Makefile. Add the following code:

CXX=(CXX)  # Add your favourite compiler here or let makefile choose default.

CXXFLAGS=-O3 -std=c++17

BOOST_ROOT=/path/to/boost
HWLOC_ROOT=/path/to/hwloc
TCMALLOC_ROOT=/path/to/tcmalloc
HPX_ROOT=/path/to/hpx

INCLUDE_DIRECTIVES=$(HPX_ROOT)/include $(BOOST_ROOT)/include $(HWLOC_ROOT)/include

LIBRARY_DIRECTIVES=-L$(HPX_ROOT)/lib $(HPX_ROOT)/lib/libhpx_init.a $(HPX_ROOT)/lib/libhpx.so $(BOOST_ROOT)/lib/libboost_atomic-mt.so $(BOOST_ROOT)/lib/libboost_filesystem-mt.so $(BOOST_ROOT)/lib/libboost_program_options-mt.so $(BOOST_ROOT)/lib/libboost_regex-mt.so $(BOOST_ROOT)/lib/libboost_system-mt.so -lpthread $(TCMALLOC_ROOT)/libtcmalloc_minimal.so $(HWLOC_ROOT)/libhwloc.so -ldl -lrt

LINK_FLAGS=$(HPX_ROOT)/lib/libhpx_wrap.a -Wl,-wrap=main  # should be left empty for HPX_WITH_HPX_MAIN=OFF

hello_world: hello_world.o
   $(CXX) $(CXXFLAGS) -o hello_world hello_world.o $(LIBRARY_DIRECTIVES) $(LINK_FLAGS)

hello_world.o:
   $(CXX) $(CXXFLAGS) -c -o hello_world.o hello_world.cpp $(INCLUDE_DIRECTIVES)

Important

LINK_FLAGS should be left empty if HPX_WITH_HPX_MAIN is set to OFF. Boost in the above example is build with --layout=tagged. Actual Boost flags may vary on your build of Boost.

To build the program, type:

make

A successful build should result in hello_world binary. To test, type:

./hello_world

How to build HPX components with makefile¶

Let’s try a more complex example involving an HPX component. An HPX component is a class that exposes HPX actions. HPX components are compiled into dynamically-loaded modules called component libraries. Here’s the source code:

hello_world_component.cpp

#include <hpx/config.hpp>
#if !defined(HPX_COMPUTE_DEVICE_CODE)
#include "hello_world_component.hpp"
#include <hpx/iostream.hpp>

#include <iostream>

namespace examples { namespace server
{
    void hello_world::invoke()
    {
        hpx::cout << "Hello HPX World!" << std::endl;
    }
}}

HPX_REGISTER_COMPONENT_MODULE();

typedef hpx::components::component<
    examples::server::hello_world
> hello_world_type;

HPX_REGISTER_COMPONENT(hello_world_type, hello_world);

HPX_REGISTER_ACTION(
    examples::server::hello_world::invoke_action, hello_world_invoke_action);
#endif

hello_world_component.hpp

#pragma once

#include <hpx/config.hpp>
#if !defined(HPX_COMPUTE_DEVICE_CODE)
#include <hpx/hpx.hpp>
#include <hpx/include/actions.hpp>
#include <hpx/include/lcos.hpp>
#include <hpx/include/components.hpp>
#include <hpx/serialization.hpp>

#include <utility>

namespace examples { namespace server
{
    struct HPX_COMPONENT_EXPORT hello_world
        : hpx::components::component_base<hello_world>
    {
        void invoke();
        HPX_DEFINE_COMPONENT_ACTION(hello_world, invoke);
    };
}}

HPX_REGISTER_ACTION_DECLARATION(
    examples::server::hello_world::invoke_action, hello_world_invoke_action);

namespace examples
{
    struct hello_world
      : hpx::components::client_base<hello_world, server::hello_world>
    {
        typedef hpx::components::client_base<hello_world, server::hello_world>
            base_type;

        hello_world(hpx::future<hpx::naming::id_type> && f)
          : base_type(std::move(f))
        {}

        hello_world(hpx::naming::id_type && f)
          : base_type(std::move(f))
        {}

        void invoke()
        {
            hpx::async<server::hello_world::invoke_action>(this->get_id()).get();
        }
    };
}

#endif

hello_world_client.cpp

#include <hpx/config.hpp>
#if defined(HPX_COMPUTE_HOST_CODE)
#include <hpx/wrap_main.hpp>

#include "hello_world_component.hpp"

int main()
{
    {
        // Create a single instance of the component on this locality.
        examples::hello_world client =
            hpx::new_<examples::hello_world>(hpx::find_here());

        // Invoke the component's action, which will print "Hello World!".
        client.invoke();
    }

    return 0;
}
#endif

Now, in the directory, create a Makefile. Add the following code:

CXX=(CXX)  # Add your favourite compiler here or let makefile choose default.

CXXFLAGS=-O3 -std=c++17

BOOST_ROOT=/path/to/boost
HWLOC_ROOT=/path/to/hwloc
TCMALLOC_ROOT=/path/to/tcmalloc
HPX_ROOT=/path/to/hpx

INCLUDE_DIRECTIVES=$(HPX_ROOT)/include $(BOOST_ROOT)/include $(HWLOC_ROOT)/include

LIBRARY_DIRECTIVES=-L$(HPX_ROOT)/lib $(HPX_ROOT)/lib/libhpx_init.a $(HPX_ROOT)/lib/libhpx.so $(BOOST_ROOT)/lib/libboost_atomic-mt.so $(BOOST_ROOT)/lib/libboost_filesystem-mt.so $(BOOST_ROOT)/lib/libboost_program_options-mt.so $(BOOST_ROOT)/lib/libboost_regex-mt.so $(BOOST_ROOT)/lib/libboost_system-mt.so -lpthread $(TCMALLOC_ROOT)/libtcmalloc_minimal.so $(HWLOC_ROOT)/libhwloc.so -ldl -lrt

LINK_FLAGS=$(HPX_ROOT)/lib/libhpx_wrap.a -Wl,-wrap=main  # should be left empty for HPX_WITH_HPX_MAIN=OFF

hello_world_client: libhpx_hello_world hello_world_client.o
  $(CXX) $(CXXFLAGS) -o hello_world_client $(LIBRARY_DIRECTIVES) libhpx_hello_world $(LINK_FLAGS)

hello_world_client.o: hello_world_client.cpp
  $(CXX) $(CXXFLAGS) -o hello_world_client.o hello_world_client.cpp $(INCLUDE_DIRECTIVES)

libhpx_hello_world: hello_world_component.o
  $(CXX) $(CXXFLAGS) -o libhpx_hello_world hello_world_component.o $(LIBRARY_DIRECTIVES)

hello_world_component.o: hello_world_component.cpp
  $(CXX) $(CXXFLAGS) -c -o hello_world_component.o hello_world_component.cpp $(INCLUDE_DIRECTIVES)

To build the program, type:

make

A successful build should result in hello_world binary. To test, type:

./hello_world

Note

Due to high variations in CMake flags and library dependencies, it is recommended to build HPX applications and components with pkg-config or CMakeLists.txt. Writing Makefile may result in broken builds if due care is not taken. pkg-config files and CMake systems are configured with CMake build of HPX. Hence, they are stable when used together and provide better support overall.

Creating HPX projects¶

Using HPX with pkg-config¶

How to build HPX applications with pkg-config¶

How to build HPX components with pkg-config¶

Using HPX with CMake-based projects¶

Using CMake targets¶

Using macros to create new targets¶

Using the HPX compiler wrapper hpxcxx¶

Optional FLAGS¶

Using macros to set up existing targets to use HPX¶

Using HPX with Makefile¶

How to build HPX applications with makefile¶

How to build HPX components with makefile¶

Using the HPX compiler wrapper `hpxcxx`¶

Optional `FLAGS`¶