For C++ projects, the build system must handle complex dependencies, ensure fast build times, and support cross-platform development. Bazel, an open-source build and test tool from Google, has emerged as a strong contender in this space.
We want to explore the benefits of using Bazel for your C++ projects. Let’s start with what Google’s build tool is.
Bazel is an advanced build system that originated from Google’s internal build tool, Blaze. It was designed to optimize the efficiency of software development, supporting multiple languages and platforms, and making it suitable for large-scale, polyglot projects. Bazel focuses on essential features for modern software development:
- High performance
- Reproducibility
- Scalability
- Dependency management
- Extensibility
There are numerous build systems, particularly within the realm of the C++ language. Why, then, opt for Bazel? The answer is simple and straightforward – it facilitates cost reduction while concurrently enhancing reliability and consistency. And it does that well.
Previously, we compared Bazel and CMake and showed their differences. Clearly, Google’s build tool has shown promise over CMake, especially for large-scale projects. Now, let's narrow the focus and explore why Bazel is a great choice.
1. Performance
Bazel's focus on speed and efficiency is particularly beneficial for C++ projects, which often involve lengthy compile times with other tools. The incremental build feature ensures that developers spend less time waiting for builds to complete, thereby increasing productivity. In other words, using Bazel results in reduced costs for building and testing.
2. Consistency and Reliability
The hermetic and deterministic nature of Bazel builds ensures that your C++ projects are built in a consistent and reliable manner. This is crucial for debugging and maintaining a stable development environment.
3. Handling Complexity
C++ projects can quickly become complex with numerous dependencies and platform-specific code. Bazel’s precise dependency management (like `bzlmod`) and scalability make it well-suited to handle such complexities.
4. Cross-Platform Support
Bazel's ability to support multiple platforms out of the box is a significant advantage for C++ projects that need to be built and tested across different operating systems and architectures.
Why does Bazel appeal as a build system for C++ projects? It stems from several key features like enhanced performance, reproducibility, scalability, and extensibility. Below, we dig deeper into these features to understand how they contribute to making Bazel an excellent choice for C++ development.
1. Speed and Efficiency
Bazel supports speed and efficiency with its features incremental builds and remote build execution.
Let’s have a look at them individually.
Incremental Builds
Incremental builds are one of Bazel's most significant advantages. When you make changes to your code, Bazel only rebuilds the affected parts of the project rather than recompiling everything. This is achieved through a comprehensive dependency analysis and tracking mechanism. By avoiding unnecessary work, Bazel significantly reduces build times and improves developer productivity.
- Dependency Graph: Bazel maintains a detailed dependency graph that tracks the relationships between different parts of the codebase. When a change is made, Bazel uses this graph to determine the minimal set of files that need to be rebuilt.
- Artifact Caching: Bazel caches build artifacts locally and remotely. If a particular artifact has already been built and cached, Bazel will reuse it instead of rebuilding it from scratch, further speeding up the build process.
Remote Build Execution
Remote build execution distributes build tasks across a cluster of remote servers, enabling parallel execution and faster completion times. This feature is particularly beneficial for large projects with lengthy compile times.
- Parallel Execution: By offloading tasks to multiple remote machines, Bazel can execute many tasks simultaneously, reducing the overall build time.
Resource Utilization: Remote execution allows developers to leverage powerful server hardware and optimize resource utilization, freeing up local machine resources for other tasks.
2. Reproducibility
If it comes down to reproducibility, Bazel offers sandboxed builds and deterministic outputs.
Hermetic Builds
Hermetic builds ensure that the build process is isolated from the environment in which it is run. This isolation means that builds are not affected by changes in the environment, such as different library versions or system configurations.
- Sandboxing: Bazel uses sandboxing to isolate build actions, ensuring that they do not depend on the state of the local machine. This guarantees that builds are repeatable and consistent across different environments.
- Dependency Lockdown: By specifying exact versions of dependencies, Bazel ensures that the same versions are used every time, eliminating discrepancies caused by dependency updates or differences.
Deterministic Outputs
Deterministic outputs mean that given the same input, Bazel will always produce the same output. This determinism is crucial for debugging and ensuring build reliability.
- Consistent Hashing: Bazel uses consistent hashing algorithms to generate unique identifiers for build actions and outputs, ensuring that identical inputs always yield identical outputs.
- Reproducible Environments: By managing dependencies and build actions precisely, Bazel ensures that the build environment is consistent and reproducible.
3. Scalability
We already talked about Bazel as a great solution when handling large-scale projects. Let’s dive into it more.
Handling Large Codebases
Bazel is designed to efficiently handle large codebases, making it suitable for complex projects with extensive source files and dependencies.
- Efficient Dependency Management: Bazel’s fine-grained dependency management ensures that even in large projects, only the necessary parts are rebuilt, optimizing build times.
- Modular Architecture: Bazel’s build architecture allows for modularization, enabling teams to work on different parts of the codebase independently without causing conflicts or inefficiencies.
Polyglot Support
Bazel supports multiple programming languages, making it ideal for projects that involve more than just C++.
- Unified Build System: With Bazel, you can use a single build system for all parts of your project, whether it involves C++, Java, Python, or other languages. This unification simplifies the build process and reduces the learning curve for developers.
Cross-Language Dependencies: Bazel can manage dependencies across different languages, ensuring that the build process is seamless and integrated.
4. Dependency Management
Dependency management in Bazel ensures all components necessary for building and testing software are correctly identified, organized, and utilized.
Precise Dependency Specifications
Bazel requires developers to explicitly specify dependencies, reducing the likelihood of hidden or implicit dependencies that can cause build failures or unexpected behavior.
- BUILD Files: Dependencies are defined in BUILD files, which are easy to read and maintain. This explicit declaration makes it clear what each part of the code depends on, improving transparency and maintainability.
- Fine-Grained Control: By specifying dependencies at a granular level, Bazel ensures that only the necessary parts of the codebase are included in the build process, optimizing performance and reducing potential conflicts.
External Dependencies
Bazel can manage external dependencies through its new `bzlmod` feature, ensuring that third-party libraries are correctly integrated and versioned.
bzlmod is Bazel's new module system designed to enhance the way external dependencies are managed. It offers a more modern, flexible, and powerful approach compared to the traditional WORKSPACE mechanism.
Key features of bzlmod:
- Centralized Dependency Management - bzlmod uses a `MODULE.bazel` file to manage dependencies, providing a clear and concise way to specify and control external libraries.
- Version Resolution - bzlmod supports sophisticated version resolution strategies, allowing you to specify version constraints and resolve conflicts automatically. This ensures that your project uses compatible versions of dependencies.
- Transitive Dependency Management - bzlmod handles transitive dependencies more effectively, ensuring that all indirect dependencies are correctly resolved and managed. This reduces the risk of dependency conflicts and simplifies dependency maintenance.
- Repository Rules - Similar to the `WORKSPACE` file, bzlmod allows you to define repository rules for fetching and managing external dependencies. However, it provides more flexibility and better integration with modern dependency management practices.
Public Registries – even though Bazel requires a `BUILD` file (a file with build recipe) for each third party library that’s engaged in the build process, developers don’t have to define them by themselves. There are public registries, such as Bazel Central Registry, that provide ready-made build recipes for the vast majority of externals.
5. Extensibility
An out-of-the-box build tool may fail to cover all the project's needs, especially in the context of bigger codebases. Let’s see ways how Bazel allows its users to customize the behavior of their build tool.
Custom Rules
Bazel allows developers to write custom build rules to extend its functionality. This flexibility ensures that Bazel can be tailored to the specific needs of any project.
- Skylark Language: Bazel’s extension language, Skylark (now known as Starlark), allows developers to create custom build rules and macros. This enables the automation of complex build processes and the integration of specialized tools.
- Rule Sharing: Custom rules can be shared across projects, promoting reuse and consistency within an organization.
Toolchains Definition
Bazel's extensibility includes the ability to add new toolchains, which define the set of tools and their configurations used for building and testing code. This allows developers to customize the build process for specific requirements.
- Define Toolchain Types and Configurations: Developers can define new toolchain types and configurations to specify the tools and their settings.
- Toolchain Implementation: By implementing the toolchain rules, developers can specify how the tools should be used for building code, enabling support for different compilers, linkers, and other build tools.
- Flexibility and Customization: Adding new toolchains ensures that Bazel can support a wide variety of build environments and requirements, enhancing its flexibility and usability.
Ecosystem Integration
Bazel integrates well with other tools and services, enhancing the overall development workflow.
- Continuous Integration: Bazel can be easily integrated into continuous integration (CI) systems, ensuring that builds and tests are run automatically with each code change.
Development Environments: Bazel supports various IDEs and text editors, providing a seamless development experience. Plugins and extensions are available for popular tools like Visual Studio Code, CLion, and others.
Choosing the right build system is a critical decision for the success of any software project. Nowadays, it’s important to improve the overall developer experience, and migration to Bazel is a big step forward. For C++ projects, Bazel offers a compelling mix of speed, reproducibility, scalability, and flexibility.
Its robust feature set and focus on efficiency make it an excellent choice for modern C++ development. By adopting Bazel, developers can ensure that their projects are built reliably, consistently, and quickly, allowing them to focus more on coding and less on managing builds.
