Concurrent programming patterns, synchronization, and thread-safety.
Go context.Context: constructors, cancellation, deadlines, request values, and five goroutine leak patterns in production.
Java singletons: enum patterns, double-checked locking, and holder-classes — and when dependency injection is the better answer.
The features that changed Java: lambdas, streams, records, sealed classes, pattern matching, and virtual threads. Java 8 to 21.
Master context.Context in Go: cancellation propagation, deadline inheritance, goroutine leak patterns, and debugging with pprof.
Java 21 virtual threads: M:N scheduling, pinning hazards, ThreadLocal pitfalls, JFR detection, and what migration really takes.
thenCompose vs thenApply, running calls in parallel with allOf, timeouts, executor selection, and production error handling.
Build a production-ready Go worker pool with goroutines and channels. Control concurrency and prevent resource exhaustion.