Building large software projects can often be time-consuming, especially when dealing with complex dependencies and build configurations. One tool that can help optimize build times is CMake. In this blog post, we will explore some techniques and best practices to improve build times with CMake.
Table of Contents
Parallel Builds
By default, CMake builds projects sequentially, i.e., one target at a time. However, if your system has multiple cores or processors, you can significantly speed up the build process by enabling parallel builds. To enable parallel builds, add the --parallel <num_threads> option when invoking CMake. For example:
cmake --build . --parallel 4
This will build up to four targets simultaneously, assuming the system has enough resources. Adjust <num_threads> according to the number of cores available on your system.
Target-Level Parallelism
CMake allows specifying dependencies between targets using the add_dependencies function. However, by default, CMake builds targets in the order they appear in the configuration files, even if there are no actual dependencies between them. This can lead to unnecessary sequential build steps and increased build times.
To optimize build times, it is essential to organize targets and their dependencies efficiently. Use the add_dependencies function to specify the actual dependencies between targets, ensuring that unrelated targets can be built in parallel.
Modular Approach
Breaking down your project into smaller, modular components can also improve build times. By making each component independent and only compiling the necessary dependencies, you can minimize the build scope and reduce unnecessary recompilation.
Consider using CMake’s add_subdirectory function to include subprojects or external dependencies as separate modules. This modular approach enables parallel builds and allows better management of dependencies.
Caching
CMake provides a powerful caching mechanism that can significantly improve build times. The caching feature allows saving intermediate build results, such as compiled objects or generated files, and reusing them in subsequent builds. This can eliminate redundant work and speed up the build process.
To enable caching, use the cmake --build . --target <target> command with the --use-internal-cache option. This will reuse cached results if available, reducing the build time for subsequent builds.
Summary
Optimizing build times with CMake requires implementing appropriate strategies and best practices. Enabling parallel builds, utilizing target-level parallelism, adopting a modular approach, and leveraging caching are some of the effective techniques to improve build times in CMake projects.
By following these optimization techniques, you can significantly reduce the time required to build your projects and improve development productivity.
#tags: CMake, build optimization