Tesla·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Tesla SWE interview where they had me implement a task scheduler from scratch, runnable and everything. Not a design question, they wanted actual working code with a test showing tasks firing at the right times.

Questions Asked (1)

Implement a runnable task scheduler that lets clients add tasks at any time, where each task has a callback and a scheduled time. Tasks must not run before their scheduled time, must run in chronological order, and the scheduler should keep running and accept new tasks while active. Include a working example demonstrating correct timing.

System DesignAlgorithms & Data StructuresTechnical Trade-offs

Author's notes

This took me a minute to even figure out where to start.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a design using a priority queue (min-heap) to order tasks by scheduled time, with a dedicated worker thread that sleeps until the next task's time. Discuss trade-offs between busy-waiting and condition variables, and demonstrate a working example with precise timing.

Pro tip: Use a condition variable with a timed wait to avoid busy-waiting and allow immediate wake-up when a new earlier task is added, showing awareness of efficiency and responsiveness.

1. Clarify Requirements and Constraints

Ask about expected load, precision of timing, whether tasks can be cancelled, and if multiple tasks can have the same scheduled time. This shows thoroughness and helps tailor the solution.

2. Design Data Structures and Concurrency Model

Propose a min-heap (priority queue) to store tasks by scheduled time, and a worker thread that waits on a condition variable until the next task is due. Ensure thread-safe access to the queue.

3. Implement Core Scheduler Logic

Write code for adding tasks (push to heap, notify condition variable) and the worker loop (wait until next task time, pop and execute tasks in order). Handle edge cases like empty queue and spurious wake-ups.

4. Demonstrate with a Working Example

Provide a runnable example that schedules tasks at different times, including adding a task after the scheduler starts, and show output with timestamps proving tasks run in order and not early.

5. Discuss Trade-offs and Extensions

Mention alternatives like using a timer wheel or ScheduledExecutorService, and discuss trade-offs in precision, scalability, and complexity. Also consider error handling and cancellation.

Key Points to Mention

Use of a min-heap (priority queue) to maintain chronological order of tasks.
Condition variable with timed wait to avoid busy-waiting and allow immediate wake-up for new tasks.
Thread safety: locking mechanisms to protect shared data structures.
Handling of tasks added while the scheduler is running (dynamic addition).
Precision of timing: how to ensure tasks don't run early (e.g., using absolute time and checking current time).
Trade-offs between different scheduling approaches (e.g., single worker vs. thread pool, busy-wait vs. condition variable).

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