Initial Python tracer based on runtime_tracing #33
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tzanko-matev
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Sep 2, 2025
tzanko-matev
commented
- We hook to the PY_START, PY_RETURN and LINE events and can record a simple trace.
- We can run the module as on a script like so:
Summary of changes
- Implemented a Rust-backed tracer using runtime_tracing.
- Added a concrete implementation of the codetracer-python-recorder/src/tracer.rs trait.
- Wired the runtime tracer into the public Python API (start/stop/flush).
Key details
- New tracer implementation: src/runtime_tracer.rs
- Struct RuntimeTracer backed by runtime_tracing::NonStreamingTraceWriter.
- Maps selected sys.monitoring events (CALL, LINE, PY_RETURN) to runtime_tracing:
- CALL: registers function and call (without capturing full arg lists yet).
- LINE: registers a Step.
- PY_RETURN: registers return value (optionally captured as ValueRecord).
-
Minimal value encoder for None, bool, int, str; falls back to Raw string for others.
-
Begins writing metadata, paths, and events on start and flushes them on finish.
-
Exposes helper derive_sidecar_paths(events_path) -> (metadata.json, paths.json).
-
Extended Tracer trait: src/tracer.rs
- Now Tracer: Send + Any (to safely store in static Mutex).
- Added downcasting support: fn as_any(&mut self) for optional future use.
- Added default lifecycle hooks:
- fn flush(&mut self, _py) -> PyResult<()> { Ok(()) }
- fn finish(&mut self, _py) -> PyResult<()> { Ok(()) }
-
Added flush_installed_tracer(py) to flush current tracer without uninstalling.
-
uninstall_tracer(py) now calls tracer.finish(py) before unhooking callbacks.
-
Python API integration: src/lib.rs
- start_tracing(path, format, capture_values, source_roots)
- Prevents double-start via ACTIVE flag.
- Creates RuntimeTracer, derives output file names:
- events: path (user-provided)
- metadata: path with extension metadata.json
- paths: path with extension paths.json
- For simplicity and to remain object-safe in this environment, “binary” maps to the non-streaming BinaryV0 writer. JSON is supported as json.
- Installs tracer via sys.monitoring and flips ACTIVE to true.
- stop_tracing()
- Uninstalls the tracer (which calls finish on the tracer) and sets ACTIVE false.
- flush_tracing()
- Calls flush_installed_tracer(py). For non-streaming formats this writes events to the file; for streaming formats (not used here) this would be a no-op by design.
- is_tracing(): returns ACTIVE.
Behavioral notes
- Formats:
- json: uses JSON non-streaming writer.
- binary: mapped to BinaryV0 non-streaming writer in this implementation to avoid relying on the private streaming writer module and to keep the tracer object Send-safe.
- Sidecar files:
- metadata: .metadata.json
- paths: .paths.json
- events:
- Values capturing:
- Optional via capture_values flag. Basic types (None, bool, int, str) are handled; all others fall back to Raw.
What I didn’t change
- Existing tests and their tracer implementations (PrintTracer, CountingTracer) remain compatible because all new Tracer methods are default no-ops.
Next steps (optional)
- Expand event interest set (e.g., exceptions, C_RETURN/C_RAISE) to record richer traces.
- Enhance value capture and variable bindings for arguments and locals (requires more Python-level context).
- Consider supporting streaming binary output once a public API for the streaming writer is exposed (or if constraints allow depending on runtime_tracing crate updates).
Commands to run
- Build and tests rely on your environment’s Python/PyO3 toolchain. The repo’s recommended way:
- just venv 3.13 dev
- just test
This implementation hooks into sys.monitoring, records with runtime_tracing, and exposes start/stop/flush in the Python module, keeping the code defensive, testable, and focused on the requested trait
implementation.
Signed-off-by: Tzanko Matev <[email protected]>
Activate tracing on script entry
codetracer-python-recorder/codetracer_python_recorder/__main__.py:
codetracer-python-recorder/codetracer_python_recorder/api.py:
codetracer-python-recorder/src/lib.rs:
codetracer-python-recorder/src/runtime_tracer.rs:
trace.json:
trace.paths.json:
Signed-off-by: Tzanko Matev <[email protected]>
Only trace files in a whitelist (experiment)
codetracer-python-recorder/codetracer_python_recorder/__main__.py:
codetracer-python-recorder/src/lib.rs:
codetracer-python-recorder/src/runtime_tracer.rs:
Signed-off-by: Tzanko Matev <[email protected]>
Ro6afF
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Sep 4, 2025
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Ro6afF
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…rgs] script.py [script args]` codetracer-python-recorder/codetracer_python_recorder/__init__.py: codetracer-python-recorder/codetracer_python_recorder/__main__.py: hello.py: trace.json: trace.metadata.json: trace.paths.json: Signed-off-by: Tzanko Matev <[email protected]>
Signed-off-by: Tzanko Matev <[email protected]>
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Fixed the issues. Will merge |
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