Discuss mutexes, memory alignment, polymorphism, idempotency

In this interview round, you are asked several conceptual software-engineering questions. Answer all parts clearly and concisely, using examples.

1. Basic mutex programming

You have a multithreaded application where multiple threads increment a shared counter and occasionally read/write fields of a shared object.

1. What is a mutex and why is it needed in this scenario?
2. Describe how you would use a mutex to protect the shared counter from data races.
3. What kinds of bugs can occur if you update shared data from multiple threads without proper synchronization?
4. Briefly compare a mutex to other primitives such as a read–write lock or a semaphore.

2. Memory efficiency and alignment

1. What is memory alignment ?
2. How can the layout/order of fields inside a struct/class affect memory efficiency because of alignment and padding?
3. Give a small example (e.g., a struct with several fields) and explain how reordering its fields could reduce memory usage.
4. Why might poor memory layout hurt performance (e.g., cache behavior)?

3. Polymorphism

1. What is polymorphism in object-oriented programming?
2. Explain the difference between compile-time (static) polymorphism and run-time (dynamic) polymorphism, with examples.
3. Give a concrete example with a base class and two derived classes where polymorphism makes the code more extensible or cleaner.

4. Idempotent operations

1. What does it mean for an operation to be idempotent ?
2. Give at least two examples of idempotent operations in software systems (for example, in APIs, databases, or distributed systems).
3. Why is idempotency important in the context of retries, failures, or distributed systems?