← Tesla Interview Insights

Tesla·Software Engineer·Technical Phone Screen·Senior

Senior
Apr 2026

Summary

Tesla SWE interview with a concurrency problem that looked deceptively manageable on the surface. The core challenge was around process scheduling and lock design, and the discussion went deeper than I expected.

Questions Asked (1)

Q1

You have 10 processes running in parallel, each needing to call a function with one of two targets (A or B). Only one process can run against a given target at a time, but both targets should stay busy whenever possible. Implement this using locks or semaphores, and discuss starvation and fairness.

System DesignTechnical Trade-offsAlgorithms & Data Structures
Author's notes

I went straight for two mutexes, one per target, which is the obvious move.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Design a solution using two semaphores (one per target) to control access, with processes acquiring the semaphore for their chosen target before calling the function. Discuss how to ensure both targets stay busy by having processes dynamically choose the less contended target, and analyze starvation and fairness implications of different selection strategies.

Pro tip: Mention that using a simple semaphore per target can lead to starvation if processes always prefer one target, so consider implementing a fair queue or a randomized selection to balance load and prevent starvation.

1. Understand the problem and constraints

Identify that there are 10 processes, each needing to call a function with target A or B, and only one process per target at a time. The goal is to keep both targets busy while avoiding starvation.

2. Choose synchronization primitives

Select semaphores or locks to represent each target. A binary semaphore per target ensures mutual exclusion for that target.

3. Design process behavior

Each process must acquire the semaphore for its chosen target before calling the function, then release it. To keep both targets busy, processes should check availability and possibly switch targets if one is idle.

4. Address starvation and fairness

Discuss how a naive approach (e.g., always preferring A) can starve B. Propose solutions like randomized target selection, round-robin, or a fair queue to ensure both targets get utilized and no process waits indefinitely.

5. Evaluate trade-offs

Compare different strategies (e.g., simple semaphores vs. fair queuing) in terms of complexity, throughput, and fairness. Highlight that fairness may reduce throughput but prevents starvation.

Key Points to Mention

  • Use of binary semaphores for mutual exclusion per target.
  • Potential for starvation if processes always prefer one target.
  • Fairness mechanisms: randomized selection, round-robin, or fair queuing.
  • Trade-off between throughput and fairness.
  • Dynamic target selection to keep both targets busy.
  • Avoiding deadlock by ensuring processes do not hold one semaphore while waiting for another.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.