Posts Tagged ‘PushPull’
[DotJs2024] Thinking About Your Code: Push vs Pull
Navigating the currents of performant code demands a lens attuned to flow dynamics, where producers and consumers dance in tandem—or discord. Ben Lesh, a veteran of high-stakes web apps from Netflix’s infrastructure dashboards to RxJS stewardship, shared this paradigm at dotJS 2024. With roots in rendering millions of devices across North America’s bandwidth, Lesh distilled decades of collaboration with elite engineers into a quartet of concepts: producers, consumers, push, pull. These primitives illuminate code’s underbelly, spotlighting concurrency pitfalls, backpressure woes, and optimal primitives for JavaScript’s asynchronous tapestry.
Lesh’s entrée was a bespoke live demo: enlisting audience volunteer Jessica Sachs to juggle M&Ms, embodying production-consumption. Pull—Jessica grabbing at will—affords control but falters asynchronously; absent timely M&Ms, hands empty. Push—Lesh feeding sequentially—frees producers for factories but risks overload, manifesting backpressure as frantic consumption. Code mirrors this: a getValue() invocation pulls synchronously, assigning to a consumer like console.log; for loops iterate pulls from arrays. Yet, actors abound: functions produce, variables consume; callbacks push events, observables compose them.
JavaScript’s arsenal spans quadrants. Pure pull: functions and intervals yield eager values. Push: callbacks for one-offs, observables for streams—RxJS’s forte, enabling operators like map or mergeMap for event orchestration. Pull-then-push hybrids: promises (function returning deferred push) and async iterables (yielding promise-wrapped results), ideal for paced delivery via for await...of, mitigating backpressure in slow consumers. Push-then-pull inverts: signals—Ember computeds, Solid observables, Angular runes—notify changes, deferring reads until render. Lesh previewed TC39 signals: subscribe for pushes, get for pulls, birthing dependency graphs that lazy-compute, tracking granular ties for efficient diffing.
This framework unveils pathologies: thread lockups from unchecked pushes, concurrency clashes in nested callbacks. Lesh advocated scanning code for actors—spotting producers hidden in APIs—and matching primitives to intent. Pull suits sync simplicity; push excels in async firehoses; hybrids temper throughput; signals orchestrate reactive UIs. As frameworks like React lean on signals for controlled reads pre-render, developers gain foresight into bottlenecks, fostering resilient, scalable architectures.
Decoding Flow Primitives in JavaScript
Lesh partitioned primitives into a revealing matrix: pull for immediacy (functions pulling values), push for autonomy (observables dispatching relentlessly). Hybrids like promises bridge, returning handles for eventual pushes; async iterables extend, pacing via awaits. Signals, the push-pull hybrid, notify sans immediate computation—perfect for UI graphs where effects propagate selectively, as in Solid’s fine-grained reactivity or Angular’s zoned eschewal.
Navigating Backpressure and Optimization
Backpressure—producers overwhelming consumers—Lesh dramatized via M&M deluge, solvable by hybrids throttling intake. Signals mitigate via lazy evals: update signals, compute only on get, weaving dependency webs that prune cascades. Lesh urged: interrogate code’s flows—who pushes/pulls?—to preempt issues, leveraging RxJS for composition, signals for reactivity, ensuring apps hum under load.