Thread-Safe LRU Cache

Design and implement a thread-safe Least Recently Used (LRU) cache. The cache must support at least the following operations:

1. get(key): Return the value associated with the key if it exists in the cache; otherwise, return an indication that the key is not found.
2. put(key, value): Insert or update the value associated with the key. If the cache reaches its capacity, it should automatically evict the least recently used item before inserting the new item.

Requirements:

• Both operations, get and put, should preferably run in O(1) time complexity.
• The cache should be thread-safe. Multiple threads should be able to access and modify the cache concurrently without causing data inconsistencies.
• Only use standard libraries available in your programming language of choice.
• Provide tests or demonstrative examples that show the thread safety and correctness of your cache under concurrent use.

Write clean, well-documented code along with any necessary explanations on how thread safety is achieved.