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SPVM-0.990158
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/ SPVM::Builder::Ninja

Name

SPVM::Builder::Ninja - Incremental Build Management using Ninja Log Format

Description

SPVM::Builder::Ninja manages incremental builds for the SPVM build system. It uses a build log format compatible with the Ninja build tool (.ninja_log) to determine if a target file needs to be regenerated.

Unlike traditional make, which relies solely on file modification times (mtime), this class provides a more robust re-generation logic by considering command-line arguments and the content hashes of dependent files.

Overview of the Build System

This class implements a high-performance and reliable build system based on the following four pillars:

1. Content-Based Re-generation (Command Hash)

To ensure build correctness, this system generates a SHA-1 hash (Command Hash) by combining various factors:

  • The command-line string itself.

  • The version of the compiler or tool used.

  • The paths and content hashes of all dependent files (e.g., header files).

This allows the system to accurately detect when a rebuild is necessary, such as when a source file is modified, an include file is changed, or a compiler flag is updated (e.g., from -O2 to -O3).

2. Ninja-Compatible Log Management

Each successful build entry is recorded in .ninja_log, including the output file name, command hash, start/end times, and mtime. This format is compatible with Ninja v5. The class also includes a "Recompact" feature that cleans up old entries and rewrites the log to prevent it from growing indefinitely.

3. Concurrency Safety via File Locking

SPVM supports parallel builds to leverage multi-core processors. To prevent data corruption when multiple processes write to the same log file, this class implements strict advisory locking (LOCK_SH / LOCK_EX) using a .ninja_lock file. This ensures that concurrent build processes can operate safely and efficiently.

4. Dependency Scanning

The system recursively scans specified directories to collect dependencies such as C/C++ header files. Since the state of these files is reflected in the command hash, any change to a deep-level header file will correctly trigger a re-compilation of the dependent source files.