Simulating Garbage Collection in Rust with Reference Counting

Implementing a full-fledged garbage collector in Rust is a complex undertaking best left to the compiler. However, understanding the principles behind garbage collection and how Rust's ownership system achieves similar goals is valuable. This challenge asks you to simulate a simplified garbage collection mechanism using reference counting to manage memory for a custom data type. This exercise will help you grasp the core concepts of memory management and how Rust's ownership model avoids many of the pitfalls of traditional garbage collection.

Problem Description

You are tasked with creating a simple garbage collection system for a custom data type called Resource. Resource represents a unit of work that consumes memory. The system should track the number of references to each Resource instance. When the reference count drops to zero, the Resource should be deallocated (in this simulation, we'll simply print a message indicating deallocation).

What needs to be achieved:

1. Create a Resource struct that holds some data (a simple String in this case).
2. Implement a ResourcePool struct that manages the allocation and deallocation of Resource instances.
3. The ResourcePool should use reference counting (Rc from the standard library) to track the number of references to each Resource.
4. When a Resource is dropped (its reference count reaches zero), the ResourcePool should print a message indicating that the resource has been deallocated.

Key Requirements:

• The ResourcePool should provide a method to create new Resource instances.
• The ResourcePool should manage the lifecycle of Resource instances, ensuring they are deallocated when no longer needed.
• The deallocation should be triggered automatically when the last reference to a Resource is dropped.

Expected Behavior:

When a new Resource is created, its reference count should be 1. When a new reference is created to the same Resource, the reference count should increment. When a reference is dropped, the reference count should decrement. When the reference count reaches 0, the Resource should be deallocated, and a message should be printed to the console.

Edge Cases to Consider:

• Multiple references to the same Resource.
• Dropping references in different orders.
• Resource creation and deallocation within loops or functions.

Examples

Example 1:

Input:
let pool = ResourcePool::new();
let resource1 = pool.create_resource("Data 1".to_string());
let resource2 = pool.create_resource("Data 2".to_string());
drop(resource1);
drop(resource2);
Output:
"Resource 'Data 1' deallocated"
"Resource 'Data 2' deallocated"
Explanation: Two resources are created.  Then, both resources are explicitly dropped, causing their reference counts to reach zero and triggering deallocation.

Example 2:

Input:
let pool = ResourcePool::new();
let resource1 = pool.create_resource("Data 1".to_string());
let resource2 = Rc::clone(&resource1); // Create a second reference
drop(resource1);
drop(resource2);
Output:
"Resource 'Data 1' deallocated"
Explanation: A resource is created. A second reference is created using `Rc::clone`. The original reference is dropped, but the reference count is still 1 due to the clone.  Finally, the clone is dropped, causing the reference count to reach zero and triggering deallocation.

Example 3: (Complex Scenario)

Input:
let pool = ResourcePool::new();
let resource1 = pool.create_resource("Data 1".to_string());
let resource2 = Rc::clone(&resource1);
{
    let resource3 = Rc::clone(&resource1);
    drop(resource3);
}
drop(resource2);
drop(resource1);
Output:
"Resource 'Data 1' deallocated"
Explanation: Demonstrates nested scopes and dropping references within them. The resource is created, then cloned multiple times.  References are dropped within a scope, and finally, the original and remaining clones are dropped, triggering deallocation.

Constraints

• The solution must be written in Rust.
• The Resource struct must contain a String field.
• The ResourcePool must use Rc for reference counting.
• The deallocation message must be printed to standard output.
• The solution should handle multiple references to the same Resource correctly.
• The solution should not use any external crates beyond the standard library.
• The code should be reasonably efficient (avoid unnecessary cloning or allocations).

Notes

• This is a simplified simulation of garbage collection. Real-world garbage collectors are significantly more complex and involve techniques like generational collection and compaction.
• Focus on understanding how reference counting works and how it can be used to manage memory.
• The drop function is crucial for triggering deallocation when a reference is no longer needed.
• Consider using a debug print statement to observe the reference count as references are created and dropped. This can be very helpful for understanding the behavior of the system.
• Think about how you would extend this system to handle more complex data types and scenarios.