Mark-and-Sweep Garbage Collector in C

A simple implementation of a mark-and-sweep garbage collector using C and pointers.

This project demonstrates the fundamental concepts of memory management, heap allocation, and object reachability. Ideal for anyone learning low-level programming, interpreters, or building a small virtual machine.

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🔹 Features

• Heap management: Allocate objects dynamically using malloc.
• Stack-based VM simulation: Track variables currently in scope.
• Mark phase: Recursively marks all reachable objects from the stack.
• Sweep phase: Frees unmarked objects and reclaims memory.
• Pairs & integers: Supports tagged union objects with integers or linked pairs.
• Dynamic GC triggering: Garbage collection runs when object count exceeds a threshold.

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🔹 Why This Project Matters

Understanding manual memory management and garbage collection algorithms is crucial for:

• Programming language interpreters
• Virtual machines
• Systems programming
• Optimizing low-level code for performance

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🔹 Project Structure

gc-c/
├── gc.c            # Core implementation
├── test.sh         # Run the program
└── README.md       # Project documentation

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🔹 How to run the program

$ ./tesh.sh

Enter the name of the C file: gc.c
🛠️ Compiling 'gc.c'...

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🔹 How It Works

1. Stack Simulation: Objects are pushed onto the VM stack as variables come into scope.

2. Mark Phase:

   • Walk the stack.
   • Recursively mark all reachable objects (avoid cycles).

3. Sweep Phase:

   • Traverse the heap list.
   • Free objects not marked in the mark phase.
   • Reset marked flags for the next GC cycle.

4. Dynamic Threshold:

   • GC is triggered when numObjects >= maxObjects.
   • maxObjects doubles after each collection to balance performance.

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🔹 Example Usage

int main() {
    VM *vm = newVM();

    pushInt(vm, 1);
    pushInt(vm, 2);
    pushPair(vm); // creates pair (1,2)

    gc(vm); // runs garbage collection

    return 0;
}

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🔹 Future Improvements

• Track the number of objects created over time.
• Implement generational GC (separating young & old objects).
• Add logging and statistics for GC runs.
• Support more complex object types and references.

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🔹 Learning Goals

This project is meant as a learning exercise:

• Understand memory management at a low level.
• Learn how garbage collectors work under the hood.
• Gain confidence with pointers, structs, and recursion in C.

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🔹 License

MIT