Concurrency

🔀 Concurrency (language-agnostic + Java + Go)

Concepts

• Concurrency vs parallelism
• Race conditions, critical sections, atomicity, visibility, ordering
• Memory models: happens-before (Java JMM, Go memory model)
• Locks: mutex, RW-lock, reentrant, spin locks; lock contention; lock-free with CAS
• Deadlock, livelock, starvation; lock ordering
• Models: shared memory + locks · message passing (CSP, Go channels) · actors · async/await
• Producer–consumer, bounded buffers, backpressure
• Thread pools, work stealing (ForkJoinPool), Little’s Law for pool sizing

Java specifics

• synchronized, volatile, java.util.concurrent (locks, atomics, latches, semaphores, ConcurrentHashMap)
• ExecutorService, CompletableFuture composition, cancellation
• Virtual threads (Java 21+): when they help (I/O bound) and when they don’t (CPU bound), pinning
• Structured concurrency and scoped values (check the status in your JDK version: preview vs final)

Go specifics

• Goroutines + the scheduler (G-M-P model), channels (buffered/unbuffered), select
• sync.Mutex, RWMutex, WaitGroup, Once, sync/atomic, errgroup
• context for cancellation/deadlines; preventing goroutine leaks
• Patterns: pipeline, fan-out/fan-in, worker pool, semaphore via buffered channel, rate limiting
• Race detector: go test -race

🧪 Labs (🟢 warm-up → 🟡 core → 🔴 hard → ⚫ boss)

• 🟢 Even/odd printer with 2 threads; dining philosophers (Java + Go)
• 🟡 Bank transfer deadlock → fix it with lock ordering → tryLock with timeout
• 🟡 Bounded blocking queue: Java (ReentrantLock + Condition) and Go (channels)
• 🔴 A concurrent LRU in both languages + benchmarks + jcstress / -race
• ⚫ Pipeline with backpressure: prove memory stays flat when the last stage is slow

🧠 Cognitive tasks

• Predict → verify: throughput of 1 mutex vs 16 stripes vs LongAdder at 32 threads
• First-principles: derive why volatile alone can’t make count++ safe
• Reverse engineering: how does singleflight avoid a thundering herd? Draw it

🛰️ Orbit integration

• Worker pool + semaphore limits per tenant in orbit-worker
• Cancellation propagation from run cancel → LLM stream close

Go deeper

⚙️ JVM Internals · Go Runtime Internals · 🧩 Concurrency Patterns

Resources

• Java Concurrency in Practice (Goetz) ⭐
• Concurrency in Go (Cox-Buday) ⭐
• Jenkov’s Java concurrency tutorials; Go blog “Share Memory By Communicating”
• The Art of Multiprocessor Programming: advanced, optional