Explain concurrency and distributed fundamentals
Company: Roku
Role: Backend Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Onsite
A backend fundamentals round covered the following topics:
1. **Multithreading in Java**: Suppose multiple threads update a shared counter and a shared map without synchronization. What bugs can happen, when do they appear, and how would you fix the code?
2. **Java hashing**: Explain how hashing works in Java collections, including the `equals` and `hashCode` contract and what happens when collisions occur.
3. **Garbage collection**: Explain Java garbage collection at a high level and what application behavior increases GC pressure or pause time.
4. **Distributed systems basics**: Compare SQL and NoSQL systems, summarize the MapReduce programming model, and explain how consistent hashing is used in distributed systems.
Quick Answer: This question evaluates understanding of concurrency and synchronization in multithreaded Java, Java hashing and equals/hashCode semantics, garbage collection behavior, and foundational distributed-systems concepts such as SQL vs NoSQL trade-offs, the MapReduce model, and consistent hashing.