Make tree iterators safe under concurrency

You have a binary tree and an inorder iterator implementation that maintains internal traversal state (e.g., a stack). Consider a multi-threaded program where: 1. Multiple threads may create and use their own iterators over the **same tree** concurrently. 2. The tree may be either **read-only** during iteration, or it may be **mutated** concurrently (inserts/deletes/rotations). ### Question How would you design the iterator and surrounding system to be **thread-safe** under these scenarios? In your answer, cover: - What is safe when the tree is read-only? - What can go wrong when the tree is mutated concurrently? - At least two approaches to handle concurrent mutations (e.g., locking, snapshotting/versioning), including trade-offs.