Salesforce·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

May 2026

Summary

Salesforce SWE interview that went deep on concurrent data structures. One big design question that branched into like four different conversations. Felt like a system design round disguised as a coding question.

Questions Asked (1)

Design insert, read, and delete operations in pseudocode for a singly linked list shared by multiple reader threads and a single writer thread. Then walk through your locking strategy, how each choice affects throughput, whether your approach risks starvation, and how you'd move toward a lock-free design using CAS.

System DesignTechnical Trade-offsAlgorithms & Data Structures

Author's notes

This one sprawled.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, then present a reader-writer lock-based solution with pseudocode for insert, read, and delete. Analyze the trade-offs in throughput and starvation, and finally outline a lock-free approach using CAS, discussing its challenges and benefits.

Pro tip: Demonstrate awareness of the ABA problem and memory reclamation challenges in lock-free designs, and mention that a hybrid approach (e.g., using locks for writes and lock-free reads) might be practical.

1. Clarify requirements and assumptions

Ask about the expected read/write ratio, thread priorities, and whether the list can be modified during traversal. State assumptions such as no duplicate keys and that reads are more frequent.

2. Design with reader-writer locks

Present pseudocode for insert, read, and delete using a reader-writer lock. Explain that multiple readers can access concurrently, but the writer requires exclusive access.

3. Analyze throughput and starvation

Discuss how reader-writer locks improve read throughput but can cause writer starvation if readers are continuous. Mention fairness policies (e.g., writer-preference) to mitigate.

4. Transition to lock-free design

Describe a lock-free approach using atomic CAS operations for insert and delete, and atomic loads for read. Explain the need for safe memory reclamation (e.g., hazard pointers, RCU).

5. Compare and conclude

Summarize trade-offs: lock-based is simpler but may limit scalability; lock-free offers better throughput but is complex and prone to subtle bugs. Recommend based on scenario.

Key Points to Mention

Reader-writer lock allows concurrent reads but exclusive writes, improving read-heavy workloads.
Writer starvation can occur if readers continuously acquire the lock; use fairness or writer-preference to prevent.
Lock-free insert/delete using CAS on next pointers, with careful handling of concurrent modifications.
ABA problem in lock-free designs and solutions like tagged pointers or hazard pointers.
Memory reclamation is critical in lock-free structures to avoid use-after-free.
Throughput considerations: lock-free scales better with more readers but has higher contention on writes.

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