The 9 Topics
1. Concurrency Models & Runtime FundamentalsWhat a 'thread' actually is in each runtime — OS threads, virtual threads, coroutines, goroutines, and the single-threaded event loop — and how many CPU cores each one can really use.2. Locks, Mutexes & Synchronized AccessThe idiomatic mutual-exclusion API in each language -- basic locks, reentrancy, reader/writer variants, and what happens when a language has no shared-memory threading model to lock at all.3. Condition Variables, Waiting & SignalingHow each language lets a thread/coroutine wait for a condition to become true and lets another wake it up -- from Java's wait/notify to Go's near-total avoidance of condition variables in favor of channels.4. Atomics, volatile & the Memory ModelVisibility vs. atomicity, volatile/@Volatile, CAS-based atomic types, and why Python and JavaScript need this machinery far less often than Java, Kotlin, and Go do.5. Thread Pools, Executors & Structured ConcurrencyHow each language runs many tasks without spawning one raw thread per task -- executor services, coroutine dispatchers, worker-pool patterns over goroutines, and the CPU-bound escape hatches for Python and Node.6. Async/Await, Futures & Non-Blocking I/OWhether the language has async/await at all, how it represents a not-yet-ready value, and the sharp foot-gun of calling a blocking function from inside async code.7. Channels & Message-Passing ConcurrencyNative channel types (or their closest analog), buffered vs. unbuffered semantics, multiplexing over several channels at once, and how to signal completion.8. Cancellation, Timeouts & Context PropagationCooperative cancellation, the idiomatic cancellation handle in each language, timing out a blocking or async call, and propagating a single cancellation signal through a chain of calls.9. Concurrent Collections, Shared State & Debugging ToolsThread-safe collections out of the box, immutability as a concurrency strategy, and how each language actually helps you find a data race or a stuck process in production.