Batch Concurrent Logs into Five-Second Windows

Design a thread-safe logger that receives records from multiple producer threads and emits batches for consecutive five-second windows. ### Constraints & Assumptions The source specifies concurrent producers and five-second batching but leaves timing and delivery policies open. For this practice design, use processing time from a monotonic clock, windows `[origin+5k, origin+5(k+1))`, and the time a record is admitted under the logger's lock. Omit empty windows. A final shutdown flush may emit the current partial window. Sink delivery must preserve batch order. ### Clarifying Questions Are windows based on arrival time or an event timestamp? What happens exactly at the boundary? Can the sink block or fail? What memory/backpressure policy is allowed? What happens at shutdown? ### What a Strong Answer Covers Atomic admission and window rotation, timer behavior, separation of shared state from slow output, ordered emission, and deterministic boundary/concurrency tests. ### Follow-up Questions What if the timer wakes late or no new log arrives after a window closes? Why can two threads flushing outside the lock reorder batches? How do retries avoid silently losing or duplicating a batch?