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Kotlin
async / await for Parallel Results
`async` returns a `Deferred<T>` — like a Future. Use it when you need a RESULT back, in parallel. Call `.await()` to get the value (suspends until ready).
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Rust
axum — Hello World HTTP Server
axum is the tokio-team's web framework — composable, type-safe handlers built on tower middleware. The hello-world is small enough to read in one screen.
Python
Run sync Iterables as async Stream
Wrap a blocking iterator so each yield happens in a worker thread — useful when integrating sync libraries (DB cursors, file iterators) into an async pipeline without rewriting them.
Java
HttpClient — Async (CompletableFuture)
`sendAsync` returns a `CompletableFuture<HttpResponse<T>>` — chain it like any other CF. Fan out N requests, wait for all with `CompletableFuture.allOf`.
Rust
tokio::spawn — Independent Tasks
`spawn` runs a future on the runtime as an independent task — fire-and-forget, or `.await` the returned `JoinHandle` to get its result. Equivalent to threads but multiplexed onto the worker pool.
Python
Async Retry with Exponential Backoff
Retry an async operation up to N times, doubling the wait each attempt with random jitter to avoid thundering herd. Predicate controls retryability so 4xx errors stop immediately.
TypeScript
Promisify a Callback Function
Convert a Node-style `(err, result)` callback API into a Promise-returning function. Type-safe via generics — the inferred Promise resolves to the original callback's result type.
Rust
tokio mpsc Channel
Async multi-producer / single-consumer channel. Producers `.send()`, the single receiver `.recv().await` items as they arrive. Bounded — the channel back-pressures producers when full.
TypeScript
Promise with Timeout
Race a promise against a timeout — if the work takes longer than `ms`, reject with a timeout error. Cancels nothing on its own (use AbortController for that), but unblocks the caller.
JavaScript
Promise All with Concurrency Limit
Runs an array of async tasks with a maximum concurrency cap, preventing you from firing hundreds of requests simultaneously. Processes items in batches, moving to the next as slots free up. Essential when hitting rate-limited APIs or processing large datasets without overwhelming the server.
Python
Async Context Manager (aiohttp pattern)
Define an async resource using `@asynccontextmanager` from contextlib. Cleaner than writing a class with __aenter__/__aexit__ for one-off wrappers.
TypeScript
Throttle (leading-edge, typed)
Pair to debounce: fire on the first call, then ignore further calls for `interval` ms. Useful for rate-limiting scroll handlers or button clicks.
Python
asyncio.gather with Errors Tolerated
`gather(*tasks)` cancels everything on the first failure — usually NOT what you want. `return_exceptions=True` lets every task finish, returning the exception in place of a result. Perfect for fan-out HTTP fetches.
Rust
Fan-Out with try_join_all
Run N async operations concurrently and collect every Result. Fails fast on the first error; `join_all` is the variant that always waits for everyone.
Rust
Async Timeout
Wrap any future in `tokio::time::timeout` to fail it if it takes too long. Returns `Err(Elapsed)` on timeout; you decide what to do next (retry, fall back, propagate).
TypeScript
Concurrency Limiter (semaphore)
Run an array of async tasks but limit concurrency to N at a time — like p-limit, in 30 lines. Preserves input order in the output array.
JavaScript
Async Sleep / Delay
Returns a Promise that resolves after a given number of milliseconds. Use with await to pause async functions without blocking the main thread. More readable than nested setTimeout callbacks and composable with other async utilities.