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Lesson 1: BLT and CMake

In this lesson, you will learn how to use BLT and CMake to configure a software project to build. RAJA and Umpire use BLT and CMake as their build systems, and so does this tutorial.

CMake is a common tool for building C++ projects and is used throughout the world. It uses information in CMakeLists.txt files located in a software project to generate configuration files to build a code project on a particular system. Then, a utility like make can be used to compile the code.

BLT provides a foundation of CMake macros and other tools that simplify the process of Building, Linking, and Testing high performance computing (HPC) applications. In particular, BLT establishes best practices for using CMake.

The goal with this lesson is not to give you a full CMake/BLT tutorial. We want to give you enough information to help get you started configuring and building the code in this tutorial.

Our top-level CMakeLists.txt file describes this project, sets some options, and then calls add_subdirectory, telling CMake to look in sub-directories for more CMakeLists.txt files.

In this lesson directory, we have a CMakeLists.txt file that describes our application. We use the blt_add_executable macro to do this.

The macro takes two (or more) arguments, and the two most important are NAME where you provide the name of the executable to be generated, and SOURCES where you list all the source code files to compile to generate the executable:

blt_add_executable(
    NAME 01_blt_cmake
    SOURCES 01_blt_cmake.cpp)

For more information on BLT, please refer to the BLT User Guide and Tutorial.

Building the Lessons

We have already run CMake for you in the container used for this tutorial to generate the make-based build system. So you are ready to compile and run the first lesson.

First, open the VSCode terminal (Shift + ^ + `), and then move to the build directory:

$ cd build

Compiling your project in a different directory than the source code is a best practice when using CMake. Once you are in the build directory, you can use the make command to compile the executable:

$ make 01_blt_cmake

You will see some output as the code is compiled. You can then run the executable:

$ ./bin/01_blt_cmake
Hello, world!

In the next lesson, we will show you how to add RAJA and Umpire as dependencies to an application.