Implementing a Concurrent HashMap (Dashmap) in Rust

Dashmap is a concurrent hash map implementation in Rust that allows for safe and efficient concurrent access from multiple threads. This challenge asks you to implement a simplified version of Dashmap, focusing on the core functionality of insertion, deletion, and iteration while ensuring thread safety. Building this will deepen your understanding of Rust's concurrency primitives and data structures.

Problem Description

You are tasked with implementing a Dashmap struct in Rust that provides a thread-safe hash map-like interface. The Dashmap should allow multiple threads to concurrently insert, delete, and iterate over key-value pairs. The core functionality to implement includes:

• Insertion: A method to insert a new key-value pair into the map. If the key already exists, the old value should be replaced with the new one.
• Deletion: A method to remove a key-value pair from the map based on the key.
• Iteration: A method that returns an iterator allowing safe concurrent access to the key-value pairs. The iterator should not allow modification of the map during iteration.
• Thread Safety: All operations must be thread-safe, meaning they should not lead to data races or other concurrency issues when accessed from multiple threads.

The Dashmap should internally use a Mutex to protect the underlying data structure (a HashMap from the standard library). The iterator should use a RwLock to allow concurrent reads while preventing writes during iteration.

Examples

Example 1:

Input:
Thread 1: insert("a", 1)
Thread 2: insert("b", 2)
Thread 1: get("a")
Thread 2: get("b")
Output:
Thread 1: Some(1)
Thread 2: Some(2)
Explanation: Two threads concurrently insert key-value pairs.  Both threads can then retrieve their respective values.

Example 2:

Input:
Thread 1: insert("a", 1)
Thread 2: delete("a")
Thread 1: get("a")
Output:
Thread 1: None
Explanation: One thread inserts a key-value pair, while another thread deletes it. The first thread's subsequent get should return None.

Example 3: (Iteration)

Input:
Thread 1: insert("a", 1)
Thread 1: insert("b", 2)
Thread 2: iterate()
Output:
Thread 2: [("a", 1), ("b", 2)] (order may vary)
Explanation:  Two threads insert key-value pairs. The second thread iterates over the map and retrieves all key-value pairs. The order of iteration is not guaranteed.

Constraints

• The underlying data structure for storing key-value pairs should be std::collections::HashMap.
• The Mutex should protect the HashMap.
• The RwLock should protect the iterator.
• The Dashmap should handle potential key collisions gracefully.
• The iterator should not allow modification of the map during iteration. Attempts to insert or delete during iteration should be ignored or result in a clear error (your choice, but document it).
• The get method should return an Option<&V> to indicate whether the key exists.
• The iterate method should return an iterator that yields (&K, &V) tuples.
• The code should be well-documented and follow Rust's coding conventions.

Notes

• Consider using Arc to share the Dashmap between threads.
• Pay close attention to the locking strategy to avoid deadlocks. Ensure that the Mutex and RwLock are acquired and released correctly.
• The iterator should provide a snapshot of the map at the time iteration begins. Changes made to the map after iteration starts should not affect the iterator's behavior.
• Error handling is not required for this challenge, but consider how you might handle errors in a production environment.
• Focus on correctness and thread safety over extreme performance optimization. Reasonable performance is expected.
• The order of elements returned by the iterator is not guaranteed.
• You are not required to implement all methods of a standard HashMap. Focus on the core functionality described above.