Everything I've written down.

Building a Thread-Safe Rate Limiter in Java

Two algorithms, one clean design, and the concurrency details that actually matter — from the token bucket all the way to a lock-free version with CAS.

Building a Thread-Safe LRU Cache

A fixed-size cache with O(1) get and put, built from a hash map and a doubly-linked list — then made thread-safe, with the one insight that makes LRU concurrency genuinely tricky: its reads write.

Building a Thread-Safe Job Scheduler

Jobs that run at a scheduled time, ordered by priority, pulled by a pool of workers. A priority queue, a lock, and one genuinely new primitive — the timed wait — with the theory to explain every line.

DDIA Chapter 5 — Replication

My Designing Data-Intensive Applications Chapter 5 notes: the three replication models, the three replication-lag guarantees, and the W + R > N quorum rule — the highest-value distributed-systems interview material, in my own words.

The Bounded Blocking Queue

One of the most-asked concurrency problems, built two ways — from raw wait/notify to ReentrantLock with conditions — with the theory you need to explain every line in a round.

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