Design user communication manager APIs

Q: Design user communication manager APIs

This is a System Design interview question from Akuna Capital for Software Engineer roles. View the full question and solution on PracHub.

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Question

In-Memory Communication Manager (Bidirectional Sessions)

Goal

Design a lightweight, in-memory manager that tracks bidirectional user-to-user sessions (think direct-message sessions). Provide 2–3 API functions:

connect(userA, userB): establish a bidirectional session.
disconnect(userA, userB): terminate the session.
clear(userA, userB): remove session state/history while keeping users connected.

Requirements

Specify method signatures (language of your choice), key data structures (e.g., hash maps, adjacency sets), and expected time/space complexities.
Discuss edge cases (duplicate connects, self-connects, missing sessions) and how to handle invalid inputs.
Describe concurrency handling and guarantees.
Include a brief testing plan.

Assume user IDs are strings (or integers) and all data lives in a single process. No persistence is required.

Design user communication manager APIs

In-Memory Communication Manager (Bidirectional Sessions)

Goal

Requirements

Solution

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