Build a Custom CompletableFuture: Async Primitive and Parallel Array Processing
Company: Google
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Technical Screen
Overview: This question evaluates a candidate's understanding of concurrency primitives, specifically the internal mechanics of future/promise abstractions such as thread-pool execution, completion state machines, and thread-safe callback registration. It tests practical software engineering skill by requiring a non-blocking fan-out/fan-in implementation for parallel array processing built on that primitive, commonly used to assess depth of multi-threading knowledge beyond basic API usage.