Designing a Concurrent Garbage Collector Simulation

Welcome back! In our previous lessons, we explored how to manage multiple operations simultaneously using advanced concurrency techniques. Building on this foundational knowledge, today’s lesson focuses on Designing a Concurrent Garbage Collector Simulation. We’ll simulate a garbage collector in a concurrent environment, linking our previous exploration of concurrency with practical memory management applications, which are crucial for optimizing large systems.

This lesson will help you deepen your understanding of:

• Thread coordination and synchronization within concurrent systems.
• Leveraging concurrency utilities to simulate complex systems.
• Creating robust applications by mimicking real-world memory management tasks.

We’ll build a simulation that reflects how garbage collectors work in modern programming environments, focusing on efficiency and system stability.

In this lesson, we’ll create a simulation of a garbage collector, where application threads allocate objects and a garbage collector thread removes unused ones. This approach mirrors how memory management happens in real-world systems with multiple processes running simultaneously.

Let’s briefly recap some key concepts we’ll be using: Thread coordination is essential when multiple threads share resources, and concurrency utilities like ConcurrentHashMap ensure safe access to shared data structures. We’ll use these tools to efficiently simulate both the allocation of objects by application threads and the cleaning of memory by the garbage collector.

The application threads simulate processes that allocate and occasionally remove references to objects. Let’s start by setting up the application thread logic.

import java.util.Map;
import java.util.Random;
import java.util.Set;

public class ApplicationThread implements Runnable {
    private final int threadId;
    private final Random random = new Random();
    private final Map<Integer, Object> heap;
    private final Set<Integer> roots;

    public ApplicationThread(int threadId, Map<Integer, Object> heap, Set<Integer> roots) {
        this.threadId = threadId;
        this.heap = heap;
        this.roots = roots;
    }
}

Here, the ApplicationThread class is initialized with a thread ID, a shared heap (a map representing memory), and a set of roots that reference active objects. Each thread will perform operations on the heap independently. The Map<Integer, Object> represents the heap, which stores objects in memory, and the Set<Integer> represents the root set, which keeps track of objects still in use by the application.