Simulated Heap

A project that simulates manual memory management, similar to how low-level languages like C handle heap memory.
Instead of letting the JVM handle allocation and garbage collection automatically, this project demonstrates how a heap could be built and managed by hand.

---

Features

• Custom Heap Simulation: Backed by a simple byte[] array
• Memory Blocks: Tracks allocated and free chunks of memory (MemoryBlock class)
• Manual Allocation (malloc): First-fit, Best-fit, Worst-fit, or Next-fit allocation strategies can be used to allocate memory blocks.
• Manual Deallocation (free): Supports freeing blocks and coalescing adjacent free blocks to reduce fragmentation.
• Simulated Pointers: Each MemoryBlock can reference other blocks.
• Root Set Management: RootSet tracks reachable memory blocks to prevent collection.
• Garbage Collection: Implements a mark-and-sweep GC that frees unreachable memory while preserving reachable blocks.
• Heap Visualization: printHeap() shows the current state of the heap for debugging.
• Garbage Collection Visualization: GCVisualizer provides a graphical view of heap changes during GC cycles.
• Memory Alignment: All allocations are aligned to 8-byte boundaries (configurable via ALIGNMENT_SIZE), ensuring proper memory layout.
• Unit Tests: Automated tests verify allocation, freeing, reading/writing, and memory alignment.
• Demo Program: Main.java runs a sequence of allocations/frees to show heap changes in action.

---

Installation

1. Clone the repository:

   git clone 
   cd simulated-heap

2. Build the project using Maven:

   mvn clean compile

3. Run the demo program:

    mvn exec:java -Dexec.mainClass="brendanddev.Main"

---

Project Structure

simulated-heap/
│
├─ src/main/java/brendanddev/
│   ├─ heap/                 # Core memory management
│   │   ├─ SimulatedHeap.java
│   │   ├─ MemoryBlock.java
│   │   └─ AllocationStrategy.java
│   │
│   ├─ gc/                   # Garbage collection components
│   │   ├─ GarbageCollector.java
│   │   └─ RootSet.java
│   │
│   ├─ visualization/        # Visualization tools
│   │   ├─ HeapVisualizer.java
│   │   └─ GCVisualizer.java
│   │
│   └─ Main.java             # Demo entry point
│
├─ src/test/java/brendanddev/
│   ├─ SimulatedHeapTest.java  # Unit tests for SimulatedHeap
│   └─ GarbageCollectorTest.java # Unit tests for GarbageCollector
│
├─ pom.xml
└─ README.md

---

Example Usage

SimulatedHeap heap = new SimulatedHeap(32);

int a = heap.malloc(8);   // allocate 8 bytes
int b = heap.malloc(8);   // allocate another 8 bytes
heap.printHeap();         // shows two allocated blocks + one free block

heap.free(a);             // free the first 8-byte block
heap.printHeap();

int c = heap.malloc(4);   // allocate 4 bytes inside the first free region
heap.printHeap();

heap.free(b);             // free the second block
heap.free(c);             // free the 4-byte block
heap.printHeap();         // entire heap is free again

// Demonstrate Garbage Collection
RootSet rootSet = heap.getRootSet();
rootSet.add(b);            // mark block 'b' as reachable
GarbageCollector gc = new GarbageCollector(heap, rootSet);
gc.collect();
heap.printHeap();          // only reachable blocks remain allocated

---

Testing

Use Maven to run all tests:

mvn test