Deferred Deletion in Rust: Implementing a Delayed Cleanup Mechanism

Many applications require resources to be cleaned up only after a certain period or after all operations involving them have concluded. This is often referred to as "deferred deletion." In Rust, a language that emphasizes memory safety and explicit resource management, implementing such a mechanism efficiently and safely requires careful consideration of ownership, lifetimes, and concurrency.

Problem Description

Your task is to design and implement a mechanism in Rust that allows for the deferred deletion of resources. This mechanism should:

Schedule Deletion: Allow a resource to be marked for deletion, but the actual deallocation should only happen after a specified delay or after a certain number of "acknowledgements" have been received.
Handle Concurrent Access: The mechanism must be thread-safe, as multiple threads might be accessing and potentially scheduling the deletion of the same resource.
Prevent Premature Deletion: Ensure that a resource is not deleted if it's still actively being used or if its scheduled deletion has been cancelled.
Resource Representation: For this challenge, a resource can be represented by a simple integer u32. The "deletion" will involve printing a message indicating the resource has been cleaned up.

Key Requirements:

A central manager (e.g., a struct) that orchestrates the deferred deletion.
A way to register resources with the manager.
A way to schedule a resource for deletion after a specified delay (in milliseconds).
A way to "cancel" a scheduled deletion before it occurs.
A mechanism to ensure the manager itself lives long enough to perform its cleanup tasks.

Expected Behavior:

When a resource is scheduled for deletion with a delay:

If no cancellation occurs within the delay, a "Resource [ID] cleaned up" message should be printed.
If the deletion is cancelled before the delay expires, no cleanup message should be printed for that specific deletion event.

Edge Cases:

Scheduling deletion for a resource that has already been deleted.
Cancelling a deletion that has already occurred or was never scheduled.
Multiple scheduled deletions for the same resource.

Examples

Example 1:

// In a main thread or a separate manager thread

// Schedule resource 1 for deletion after 100ms
// Schedule resource 2 for deletion after 200ms

// After 150ms, cancel deletion for resource 1

// After 300ms, observe the output

Output:

Resource 2 cleaned up

Explanation: Resource 1's deletion was scheduled but then cancelled before the 100ms delay. Resource 2's deletion was scheduled for 200ms and occurred as planned.

Example 2:

// In a main thread or a separate manager thread

// Schedule resource 3 for deletion after 50ms
// Schedule resource 3 for deletion again after 150ms (effectively replacing the first schedule)

// After 100ms, cancel deletion for resource 3

// After 200ms, observe the output

Output:

(No output related to resource 3)

Explanation: The second scheduling of resource 3 overwrites the first. The cancellation then removes the pending deletion for resource 3 before the 150ms delay expires.

Example 3:

// In a main thread or a separate manager thread

// Schedule resource 4 for deletion after 50ms
// After 60ms, attempt to cancel deletion for resource 4

Output:

Resource 4 cleaned up

Explanation: The deletion for resource 4 occurred before the cancellation request could be processed effectively by the manager.

Constraints

The maximum number of unique resources to manage at any given time is 1000.
The maximum delay for deletion is 5000 milliseconds (5 seconds).
The manager should be able to handle up to 100 concurrent requests to schedule or cancel deletions.
The cleanup operations themselves are considered instantaneous for the purpose of this challenge.

Notes

Consider using std::sync::{Mutex, Arc} for thread-safe sharing of the manager's state.
The std::thread::sleep function can be useful for simulating delays, but for a more robust solution in a real-world scenario, you might consider asynchronous runtimes like tokio or async-std and their scheduling capabilities.
You'll need a way to keep track of scheduled deletions, perhaps using a HashMap where the key is the resource ID and the value is some identifier for the pending task that can be cancelled.
Think about how to manage the lifetime of the threads or background tasks responsible for performing the actual cleanup. A common pattern is to have a "shutdown" signal.

Deferred Deletion in Rust: Implementing a Delayed Cleanup Mechanism

Problem Description

Your task is to design and implement a mechanism in Rust that allows for the deferred deletion of resources. This mechanism should:

Schedule Deletion: Allow a resource to be marked for deletion, but the actual deallocation should only happen after a specified delay or after a certain number of "acknowledgements" have been received.
Handle Concurrent Access: The mechanism must be thread-safe, as multiple threads might be accessing and potentially scheduling the deletion of the same resource.
Prevent Premature Deletion: Ensure that a resource is not deleted if it's still actively being used or if its scheduled deletion has been cancelled.
Resource Representation: For this challenge, a resource can be represented by a simple integer u32. The "deletion" will involve printing a message indicating the resource has been cleaned up.

Key Requirements:

A central manager (e.g., a struct) that orchestrates the deferred deletion.
A way to register resources with the manager.
A way to schedule a resource for deletion after a specified delay (in milliseconds).
A way to "cancel" a scheduled deletion before it occurs.
A mechanism to ensure the manager itself lives long enough to perform its cleanup tasks.

Expected Behavior:

When a resource is scheduled for deletion with a delay:

If no cancellation occurs within the delay, a "Resource [ID] cleaned up" message should be printed.
If the deletion is cancelled before the delay expires, no cleanup message should be printed for that specific deletion event.

Edge Cases:

Scheduling deletion for a resource that has already been deleted.
Cancelling a deletion that has already occurred or was never scheduled.
Multiple scheduled deletions for the same resource.

Examples

Example 1:

// In a main thread or a separate manager thread

// Schedule resource 1 for deletion after 100ms
// Schedule resource 2 for deletion after 200ms

// After 150ms, cancel deletion for resource 1

// After 300ms, observe the output

Output:

Resource 2 cleaned up

Explanation: Resource 1's deletion was scheduled but then cancelled before the 100ms delay. Resource 2's deletion was scheduled for 200ms and occurred as planned.

Example 2:

// In a main thread or a separate manager thread

// Schedule resource 3 for deletion after 50ms
// Schedule resource 3 for deletion again after 150ms (effectively replacing the first schedule)

// After 100ms, cancel deletion for resource 3

// After 200ms, observe the output

Output:

(No output related to resource 3)

Explanation: The second scheduling of resource 3 overwrites the first. The cancellation then removes the pending deletion for resource 3 before the 150ms delay expires.

Example 3:

// In a main thread or a separate manager thread

// Schedule resource 4 for deletion after 50ms
// After 60ms, attempt to cancel deletion for resource 4

Output:

Resource 4 cleaned up

Explanation: The deletion for resource 4 occurred before the cancellation request could be processed effectively by the manager.

Constraints

The maximum number of unique resources to manage at any given time is 1000.
The maximum delay for deletion is 5000 milliseconds (5 seconds).
The manager should be able to handle up to 100 concurrent requests to schedule or cancel deletions.
The cleanup operations themselves are considered instantaneous for the purpose of this challenge.

Notes

Consider using std::sync::{Mutex, Arc} for thread-safe sharing of the manager's state.
The std::thread::sleep function can be useful for simulating delays, but for a more robust solution in a real-world scenario, you might consider asynchronous runtimes like tokio or async-std and their scheduling capabilities.
You'll need a way to keep track of scheduled deletions, perhaps using a HashMap where the key is the resource ID and the value is some identifier for the pending task that can be cancelled.
Think about how to manage the lifetime of the threads or background tasks responsible for performing the actual cleanup. A common pattern is to have a "shutdown" signal.