concurrency-async-patterns

Race conditions occur when concurrent async operations read-modify-write shared state. Use an async mutex to serialize access in application code, or use database transactions with SELECT FOR UPDATE to lock rows during updates.

Use Promise.all when all operations must succeed and results are interdependent. Use Promise.allSettled when operations are independent and partial failure is acceptable, since it returns every result with its fulfillment status.

Create an AbortController, call setTimeout to abort after the timeout, and pass controller.signal to fetch. Always clear the timeout in a finally block so a successful fetch does not leave a timer that fires later.

Debounce delays execution until input stops changing, resetting the timer on each call, ideal for search inputs. Throttle executes at most once per interval during continuous activity, ideal for scroll or mouse move handlers.

Node.js terminates on unhandled rejections because they indicate lost errors. Every promise must be awaited inside try/catch or have a .catch() handler; never fire-and-forget an async call without error handling.

Use a batch processing pattern that keeps a set of in-flight promises and awaits Promise.race whenever the set reaches the concurrency limit. This processes items in parallel without exhausting connections or memory.