MiniGC

A minimal mark-and-sweep garbage collector implementation in C.

Overview

MiniGC is an educational implementation of a simple garbage collector that uses the mark-and-sweep algorithm. It demonstrates fundamental GC concepts including object allocation, reachability analysis, and automatic memory reclamation.

Features

• Mark-and-Sweep Algorithm: Implements the classic two-phase garbage collection
• Stack-based VM: Uses a virtual machine with a stack to manage object references
• Two Object Types: Supports integers and pairs (cons cells)
• Cycle Detection: Handles circular references without infinite loops
• Dynamic Threshold: Automatically adjusts GC trigger threshold based on live objects

How It Works

1. Mark Phase: Traverses all reachable objects from the stack and marks them as alive
2. Sweep Phase: Reclaims memory from unmarked (dead) objects and resets marks for the next cycle
3. Automatic Triggering: GC runs when the number of objects reaches a threshold

Building and Running

gcc main.c -o minigc
./minigc

Tests

The program includes four test cases:

• Test 1: Objects on stack are preserved
• Test 2: Dead objects are collected
• Test 3: Nested objects are reached
• Test 4: Circular references are handled correctly

Implementation Details

• Initial threshold: 8 objects
• Stack capacity: 256 objects
• Threshold adjustment: Doubles after each GC cycle (or resets to 8 if no objects remain)

Educational Purpose

This project is designed for learning purposes to understand:

• How garbage collectors work
• Memory management in programming languages
• The mark-and-sweep algorithm
• Handling object graphs and cycles