Concurrent Queue Implementation in Rust

This challenge asks you to implement a thread-safe queue data structure in Rust. Concurrent queues are essential for building concurrent applications where multiple threads need to safely share and process data. Successfully completing this challenge demonstrates your understanding of Rust's concurrency primitives and memory safety guarantees.

Problem Description

You are tasked with creating a ConcurrentQueue struct in Rust that provides thread-safe enqueue and dequeue operations. The queue should be able to handle multiple producers (threads adding elements) and multiple consumers (threads removing elements) concurrently without data races or other concurrency issues.

What needs to be achieved:

• Implement a ConcurrentQueue struct with enqueue and dequeue methods.
• Ensure that enqueue and dequeue are thread-safe, meaning they can be called concurrently from multiple threads without causing data corruption or unexpected behavior.
• The queue should block when empty during dequeue and when full (if a maximum size is implemented) during enqueue.

Key Requirements:

• Thread Safety: The queue must be safe for concurrent access from multiple threads. Use appropriate synchronization primitives (e.g., Mutex, Condvar) to protect shared data.
• Enqueue: The enqueue method should add an element to the rear of the queue.
• Dequeue: The dequeue method should remove and return an element from the front of the queue. It should return an Option<T>: Some(element) if an element was dequeued, and None if the queue was empty.
• Blocking Behavior: The dequeue method should block if the queue is empty until an element becomes available. The enqueue method should block if a maximum queue size is specified and the queue is full until space becomes available.
• Generic Type: The queue should be generic, allowing it to store elements of any type T.

Expected Behavior:

• Multiple threads can enqueue elements concurrently.
• Multiple threads can dequeue elements concurrently.
• Enqueue and dequeue operations should be atomic and consistent.
• The queue should maintain FIFO (First-In, First-Out) order.
• Dequeue should not return an element until it's actually available.
• Enqueue should not block indefinitely if the queue is full (if a maximum size is implemented).

Edge Cases to Consider:

• Empty queue: dequeue should return None and potentially block.
• Full queue (if maximum size is implemented): enqueue should block until space is available.
• Multiple threads attempting to dequeue from an empty queue simultaneously.
• Multiple threads attempting to enqueue to a full queue simultaneously.
• Panics during enqueue/dequeue should be handled gracefully (e.g., by returning an error).

Examples

Example 1:

Input:
Thread 1: enqueue(1)
Thread 2: enqueue(2)
Thread 1: dequeue()
Thread 2: dequeue()
Output:
Thread 1: Some(1)
Thread 2: Some(2)
Explanation: Elements are enqueued and dequeued in FIFO order.

Example 2:

Input:
Thread 1: enqueue(1)
Thread 2: dequeue()  (queue is empty, thread blocks)
Thread 3: enqueue(2)
Thread 2: dequeue()
Output:
Thread 2: Some(1)
Thread 3: (no output immediately, enqueue doesn't block)
Thread 1: (no output)
Explanation: Thread 2 blocks until an element is enqueued.

Example 3: (with a maximum queue size of 2)

Input:
Thread 1: enqueue(1)
Thread 2: enqueue(2)
Thread 3: enqueue(3) (queue is full, thread blocks)
Thread 1: dequeue()
Thread 3: enqueue(4) (Thread 3 can now enqueue)
Thread 2: dequeue()
Output:
Thread 1: Some(1)
Thread 2: Some(2)
Thread 3: Some(4)
Explanation: Thread 3 blocks until an element is dequeued.

Constraints

• Maximum Queue Size (Optional): You can optionally implement a maximum queue size. If implemented, the maximum size should be configurable during queue creation.
• Performance: While correctness is paramount, strive for reasonable performance. Avoid unnecessary locking or copying.
• Error Handling: Consider how to handle potential errors (e.g., panics during enqueue/dequeue). Returning Result types is a good approach.
• Memory Safety: The code must be memory-safe and free from data races. Rust's ownership and borrowing system should be leveraged to ensure this.

Notes

• Rust's Mutex and Condvar are your primary tools for implementing thread safety.
• Consider using channels for communication between threads if a bounded queue is implemented.
• Think carefully about the order of acquiring and releasing locks to avoid deadlocks.
• Test your implementation thoroughly with multiple threads and various scenarios to ensure correctness and performance.
• The optional maximum queue size adds complexity but is a common requirement in real-world concurrent queues. If you choose to implement it, ensure that enqueue blocks when the queue is full and dequeue unblocks when space becomes available.