Concurrency for LLD

Thread, Process, Runnable, Callable, Future — the units and handles of concurrent work.

6 min 1 code practice

synchronized, volatile, Lock, ReentrantLock, ReadWriteLock — the mechanisms, and critically, what each one is (not) for.

7 min 1 code practice

AtomicInteger, AtomicLong, ConcurrentHashMap, BlockingQueue — the toolbox that removes most manual locking.

6 min 1 code practice

ExecutorService, ThreadPoolExecutor, its queue, worker threads and rejection policy — the operational half of concurrency.

7 min 1 diagram 1 code practice

Two threads interleave on shared state and the result depends on timing — the bug class every LLD question secretly tests.

7 min 1 diagram 1 code practice

Thread A holds lock 1 and wants lock 2; thread B holds lock 2 and wants lock 1 — both wait forever.

6 min 1 diagram practice

The performance/readability trade: when to use synchronized/locks vs CAS atomics.

6 min practice

The fundamental async pattern: producers enqueue, consumers dequeue — decoupling, back-pressure, and rate mismatch handling.

7 min 1 diagram 1 code practice

Phase 2's singleton, now graded under concurrency: the four safe forms and why naive lazy init crashes with two threads.

6 min practice

Applying everything in this phase to the limiter: per-key state, atomic claims, and the shared-map granularity decision.

6 min practice

Building the Phase 10 cache-aside in-process first: thread-safe read/write, single-flight, and eviction under concurrency.

7 min 1 code practice