Make a Racy BankAccount Deposit Thread-Safe Without Editing the Class, in Python and Go

Make a Racy BankAccount Deposit Thread-Safe Without Editing the Class, in Python and Go

Company: xAI

Role: Software Engineer

Category: Software Engineering Fundamentals

Difficulty: medium

Interview Round: Onsite

Overview: A concurrency question built around a BankAccount class whose deposit method reads the balance, sleeps, then writes it back. Candidates find every race, make deposits thread-safe through a subclass or wrapper without editing or copying the class, and carry the fix over to Go, which has no inheritance.