temporal·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

May 2026Remote

Summary

Temporal SWE interview threw a concurrency design problem at me that looked deceptively simple on the surface. The real meat was in the early-exit behavior and what you do with threads still running after you get your answer.

Questions Asked (1)

You have a slow API function that takes 1 to 10 seconds and returns a boolean. Given a list of indices, implement a function that runs the API calls in parallel and returns true as soon as any single call returns true, without waiting for the rest to finish.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

My first instinct was a thread pool with map() and I wrote that out, then they asked me to walk through what happens when the first True comes back.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: the function should return true as soon as any API call returns true, and false only if all calls return false. Then, describe a parallel execution strategy using promises or futures, with a mechanism to short-circuit on the first true result and cancel or ignore pending calls. Finally, discuss trade-offs such as resource cleanup, error handling, and potential race conditions.

Pro tip: Mention that you would use a shared flag or a promise that resolves once, ensuring that only the first true result triggers the return, and that you would handle cleanup of pending calls to avoid resource leaks. This shows awareness of production concerns beyond just correctness.

1. Clarify requirements and constraints

Confirm that the function should return true immediately when any call returns true, and false only after all calls complete with false. Ask about error handling, cancellation support, and whether the API calls can be aborted.

2. Choose a parallel execution model

Select an approach such as spawning a thread per call, using a thread pool, or using asynchronous I/O (e.g., Promises, async/await, CompletableFuture). Consider the language and environment.

3. Implement short-circuiting logic

Use a shared atomic flag or a promise that resolves once. When any call returns true, set the flag and return true immediately. Ensure that other calls are either cancelled or their results ignored.

4. Handle cleanup and resource management

If cancellation is supported, cancel pending calls to free resources. Otherwise, ensure that pending calls do not cause issues (e.g., unhandled rejections) and that the function returns promptly.

5. Discuss trade-offs and edge cases

Talk about the cost of spawning many parallel calls, potential rate limiting, error propagation, and how to handle the case where all calls return false. Mention testing strategies.

Key Points to Mention

Use of promises/futures or async/await for parallel execution
Short-circuiting with a shared flag or Promise.race
Cancellation of pending API calls to avoid resource leaks
Error handling: what if some calls fail? Should failures be ignored or propagated?
Concurrency limits: avoid overwhelming the system with too many parallel calls
Testing: how to simulate slow API calls and verify early return

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