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## Summary Implements the `--cpu-prof` CLI flag for Bun to profile CPU usage and save results in Chrome CPU Profiler JSON format, compatible with Chrome DevTools and VSCode. ## Implementation Details - Uses JSC's `SamplingProfiler` to collect CPU samples during execution - Converts samples to Chrome CPU Profiler JSON format on exit - Supports `--cpu-prof-name` to customize output filename - Supports `--cpu-prof-dir` to specify output directory - Default filename: `CPU.YYYYMMDD.HHMMSS.PID.0.001.cpuprofile` ## Key Features ✅ **Chrome DevTools Compatible** - 100% compatible with Node.js CPU profile format ✅ **Absolute Timestamps** - Uses wall clock time (microseconds since epoch) ✅ **1ms Sampling** - Matches Node.js sampling frequency for comparable granularity ✅ **Thread-Safe** - Properly shuts down background sampling thread before processing ✅ **Memory-Safe** - Uses HeapIterationScope and DeferGC for safe heap access ✅ **Cross-Platform** - Compiles on Windows, macOS, and Linux with proper path handling ## Technical Challenges Solved 1. **Heap Corruption** - Fixed by calling `profiler->shutdown()` before processing traces 2. **Memory Safety** - Added `HeapIterationScope` and `DeferGC` when accessing JSCells 3. **Timestamp Accuracy** - Explicitly start stopwatch and convert to absolute wall clock time 4. **Path Handling** - Used `bun.path.joinAbsStringBufZ` with proper cwd resolution 5. **Windows Support** - UTF-16 path conversion for Windows compatibility 6. **Atomic Writes** - Used `bun.sys.File.writeFile` with ENOENT retry ## Testing All tests pass (4/4): - ✅ Generates profile with default name - ✅ `--cpu-prof-name` sets custom filename - ✅ `--cpu-prof-dir` sets custom directory - ✅ Profile captures function names Verified format compatibility: - JSON structure matches Node.js exactly - All samples reference valid nodes - Timestamps use absolute microseconds since epoch - Cross-platform compilation verified with `bun run zig:check-all` ## Example Usage ```bash # Basic usage bun --cpu-prof script.js # Custom filename bun --cpu-prof --cpu-prof-name my-profile.cpuprofile script.js # Custom directory bun --cpu-prof --cpu-prof-dir ./profiles script.js ``` Output can be opened in Chrome DevTools (Performance → Load Profile) or VSCode's CPU profiling viewer. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Bot <claude-bot@bun.sh> Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com>