Implementing a Basic Mark and Sweep Garbage Collector in Rust

This challenge asks you to implement a simplified version of the mark and sweep garbage collection algorithm in Rust. Garbage collection is a crucial technique for automatic memory management, preventing memory leaks and simplifying development by relieving programmers from manual memory allocation and deallocation. This exercise will help you understand the core principles of garbage collection and how it works.

Problem Description

You are tasked with creating a rudimentary mark and sweep garbage collector. The collector will manage a set of objects, tracking their reachability from a set of root objects. The algorithm should consist of two phases: marking and sweeping.

What needs to be achieved:

1. Object Representation: Define a simple Object struct that can hold data and a reference to its parent (for demonstration purposes, the parent isn't strictly necessary for the core algorithm, but it allows for creating object graphs).
2. Root Set: Maintain a set of "root" objects. These are objects that are considered always reachable and are the starting point for the marking phase.
3. Marking Phase: Starting from the root objects, recursively traverse the object graph, marking each reachable object. A simple boolean flag marked within the Object struct will indicate whether an object has been marked.
4. Sweeping Phase: Iterate through all objects. Any object that has not been marked during the marking phase is considered unreachable and should be "collected" (in this simplified version, collection means resetting the marked flag and potentially freeing the memory – for this challenge, we'll just reset the marked flag).
5. Collection Cycle: Implement a function collect that performs both the marking and sweeping phases.

Key Requirements:

• The collector should correctly identify and "collect" unreachable objects.
• Reachable objects (including roots) should retain their marked status after collection.
• The code should be well-structured and readable.
• The Object struct should be generic to allow for different data types.

Expected Behavior:

The collect function should take a vector of root objects as input. It should then traverse the object graph, marking reachable objects and sweeping (resetting marked flag) unreachable objects. After the collect function is called, any object not reachable from the roots should have its marked flag set to false.

Edge Cases to Consider:

• Circular References: The object graph may contain circular references (e.g., object A points to object B, and object B points to object A). The marking phase must handle these correctly to avoid infinite loops.
• Empty Root Set: If the root set is empty, all objects should be considered unreachable and swept.
• No Reachable Objects: If all objects are unreachable from the roots, all objects should be swept.

Examples

Example 1:

Input:
Roots: [Object { data: 10, marked: false, parent: None }, Object { data: 20, marked: false, parent: None }]
Objects: [Object { data: 10, marked: false, parent: None }, Object { data: 20, marked: false, parent: None }, Object { data: 30, marked: false, parent: None }]
(Object 10 points to Object 30, Object 20 points to Object 30)

Output:
Objects: [Object { data: 10, marked: true, parent: None }, Object { data: 20, marked: true, parent: None }, Object { data: 30, marked: true, parent: None }]
Explanation: Objects 10 and 20 are roots, so they are marked. Object 30 is reachable from both 10 and 20, so it is also marked.

Example 2:

Input:
Roots: [Object { data: 10, marked: false, parent: None }]
Objects: [Object { data: 10, marked: false, parent: None }, Object { data: 20, marked: false, parent: None }, Object { data: 30, marked: false, parent: None }]
(Object 10 points to Object 20, Object 20 points to Object 30)

Output:
Objects: [Object { data: 10, marked: true, parent: None }, Object { data: 20, marked: true, parent: None }, Object { data: 30, marked: true, parent: None }]
Explanation: Object 10 is a root, so it is marked. Object 20 is reachable from 10, and Object 30 is reachable from 20, so they are also marked.

Example 3: (Edge Case - Circular Reference)

Input:
Roots: [Object { data: 10, marked: false, parent: None }]
Objects: [Object { data: 10, marked: false, parent: None }, Object { data: 20, marked: false, parent: None }]
(Object 10 points to Object 20, Object 20 points to Object 10)

Output:
Objects: [Object { data: 10, marked: true, parent: None }, Object { data: 20, marked: true, parent: None }]
Explanation: The marking phase correctly handles the circular reference between 10 and 20, marking both as reachable.

Constraints

• The number of objects managed by the collector will be less than or equal to 1000.
• The data stored within each Object can be any type T.
• The marking and sweeping phases should complete within a reasonable time (e.g., less than 1 second) for the given constraints.
• The code must be valid Rust code and compile without warnings.

Notes

• This is a simplified implementation. A real-world garbage collector would be significantly more complex, handling memory allocation, compaction, and other optimizations.
• Consider using a HashSet to store the root objects for efficient lookup.
• The marking phase can be implemented using a recursive depth-first search (DFS) algorithm. Be careful to avoid stack overflows with very deep object graphs. An iterative approach using a stack might be more robust.
• The sweeping phase can be implemented by iterating through all objects and checking their marked flag.
• Focus on correctness and clarity over performance in this exercise. The goal is to understand the fundamental concepts of mark and sweep.