State Snapshot Instrumenter

Overview

This skill instruments programs to capture snapshots of key program states at runtime. Snapshots include variable values, memory state, call stacks, and execution context, saved in structured JSON format for analysis, debugging, reproduction, and verification.

Quick Start

Basic Workflow

1. Add snapshot markers to your code (manual mode) or use automatic instrumentation
2. Run the instrumenter to generate instrumented code
3. Execute the instrumented program to capture snapshots
4. Analyze snapshots to understand program behavior

Example: Python

# 1. Add markers to your code
# def my_function(x):
#     __SNAPSHOT__("my_function:start")
#     result = x * 2
#     __SNAPSHOT__("my_function:end")
#     return result

# 2. Instrument the code
python scripts/instrument_python.py my_program.py --mode manual

# 3. Run instrumented program
python my_program_instrumented.py
# Snapshots saved to snapshots.json

# 4. Analyze snapshots
python scripts/analyze_snapshots.py snapshots.json --list

Example: C/C++

# 1. Add markers to your code
# int main() {
#     __SNAPSHOT__("main:start");
#     int x = 10;
#     __SNAPSHOT__("main:end");
#     return 0;
# }

# 2. Instrument the code
python scripts/instrument_c.py program.c --mode manual

# 3. Compile with runtime
gcc program_instrumented.c scripts/snapshot_runtime.c -o program -rdynamic

# 4. Run and analyze
./program
python scripts/analyze_snapshots.py snapshots.json --list

Example: Java

# 1. Add markers to your code
# public static void main(String[] args) {
#     __SNAPSHOT__("main:start");
#     int x = 10;
#     __SNAPSHOT__("main:end");
# }

# 2. Instrument the code
python scripts/instrument_java.py Program.java --mode manual

# 3. Compile and run
cp scripts/SnapshotRuntime.java snapshot/
javac snapshot/SnapshotRuntime.java
javac Program_instrumented.java
java Program_instrumented

# 4. Analyze
python scripts/analyze_snapshots.py snapshots.json --list

Instrumentation Modes

Manual Mode (Recommended for Targeted Debugging)

Add explicit __SNAPSHOT__("location") markers at specific points in your code.

Python:

def process_data(items):
    __SNAPSHOT__("process_data:entry")

    result = []
    for item in items:
        __SNAPSHOT__("loop_iteration")
        result.append(item * 2)

    __SNAPSHOT__("process_data:exit")
    return result

C/C++:

int calculate(int x, int y) {
    __SNAPSHOT__("calculate:entry");

    int result = x + y;

    __SNAPSHOT__("calculate:exit");
    return result;
}

Java:

public int calculate(int x, int y) {
    __SNAPSHOT__("calculate:entry");

    int result = x + y;

    __SNAPSHOT__("calculate:exit");
    return result;
}

Instrument:

python scripts/instrument_python.py file.py --mode manual
python scripts/instrument_c.py file.c --mode manual
python scripts/instrument_java.py file.java --mode manual

Automatic Mode (Comprehensive Coverage)

Automatically instrument all function/method entry and exit points.

python scripts/instrument_python.py file.py --mode auto
python scripts/instrument_c.py file.c --mode auto
python scripts/instrument_java.py file.java --mode auto

This captures state at every function boundary without manual markers.

Core Operations

1. Instrumentation

Python:

# Manual mode
python scripts/instrument_python.py input.py --mode manual -o output.py

# Automatic mode
python scripts/instrument_python.py input.py --mode auto -o output.py

# In-place modification
python scripts/instrument_python.py input.py --mode manual --inplace

C/C++:

# Instrument
python scripts/instrument_c.py input.c --mode manual -o output.c

# Compile with runtime
gcc output.c scripts/snapshot_runtime.c -o program -rdynamic

# Run with custom output file
SNAPSHOT_OUTPUT=my_snapshots.json ./program

Java:

# Instrument
python scripts/instrument_java.py Input.java --mode manual -o Output.java

# Setup runtime
cp scripts/SnapshotRuntime.java snapshot/
javac snapshot/SnapshotRuntime.java

# Compile and run
javac Output.java
SNAPSHOT_OUTPUT=my_snapshots.json java Output

2. Snapshot Analysis

List all snapshots:

python scripts/analyze_snapshots.py snapshots.json --list

Show detailed snapshot:

python scripts/analyze_snapshots.py snapshots.json --show 5

View execution timeline:

python scripts/analyze_snapshots.py snapshots.json --timeline

Track variable changes:

python scripts/analyze_snapshots.py snapshots.json --track-var "user_id"

Compare two snapshots:

python scripts/analyze_snapshots.py snapshots.json --compare 10 20

Filter snapshots:

# By location
python scripts/analyze_snapshots.py snapshots.json --filter-location "main"

# By type
python scripts/analyze_snapshots.py snapshots.json --filter-type "function_entry"

3. Runtime Control

Python:

import snapshot_runtime

# Disable snapshots temporarily
snapshot_runtime.disable()
# ... performance-critical code ...
snapshot_runtime.enable()

# Set custom output file
snapshot_runtime.set_output_file("custom.json")

# Manually save snapshots
snapshot_runtime.save_snapshots()

C/C++:

#include "snapshot_runtime.h"

snapshot_disable();
// ... performance-critical code ...
snapshot_enable();

snapshot_finalize();  // Manually save

Java:

import snapshot.SnapshotRuntime;

SnapshotRuntime.disable();
// ... performance-critical code ...
SnapshotRuntime.enable();

SnapshotRuntime.setOutputFile("custom.json");
SnapshotRuntime.saveSnapshots();

Use Cases

Bug Debugging

Capture comprehensive state to understand complex bugs:

1. Instrument with automatic mode for full coverage
2. Run to reproduce the bug
3. Analyze snapshots to identify failure point
4. Track variable changes to understand root cause

See references/use_cases.md for detailed debugging workflows.

Test Case Reproduction

Extract exact inputs and state to reproduce failures:

1. Instrument with manual snapshots at key points
2. Capture failing execution
3. Extract input dependencies from snapshots
4. Reconstruct minimal test case

See references/use_cases.md for reproduction workflows.

Formal Verification

Generate execution traces for verification tools:

1. Instrument function boundaries
2. Collect execution traces
3. Extract invariants and contracts
4. Feed to verification tools

See references/use_cases.md for verification workflows.

Reference Documentation

• `references/instrumentation_guide.md` - Comprehensive guide on instrumenting programs, including language-specific instructions, best practices, and troubleshooting
• `references/snapshot_format.md` - Complete specification of the JSON snapshot format, including language-specific variations and serialization rules
• `references/use_cases.md` - Detailed workflows for debugging, reproduction, verification, performance analysis, and concurrency debugging

Example Programs

Example instrumented programs are provided in assets/:

• example_python.py - Python example with manual snapshots
• example_c.c - C example with manual snapshots
• example_java.java - Java example with manual snapshots

Output Format

All snapshots are saved in unified JSON format:

{
  "format_version": "1.0",
  "language": "python",
  "total_snapshots": 5,
  "snapshots": [
    {
      "snapshot_id": 1,
      "timestamp": "2026-02-17T19:30:45",
      "location": "main:start",
      "type": "manual",
      "call_stack": [...],
      "local_variables": {...}
    }
  ]
}

See assets/snapshot_schema.json for the complete JSON schema.

Tips

• Use manual mode for targeted debugging to minimize overhead
• Use automatic mode for comprehensive execution understanding
• Disable snapshots in performance-critical sections
• Use descriptive location names (e.g., "function:entry", "after_operation")
• Set custom output files with SNAPSHOT_OUTPUT environment variable
• Analyze snapshots incrementally as you debug
• Compare snapshots to identify when state becomes incorrect
• Track key variables through execution to understand data flow