75 lines
2.5 KiB
JavaScript
75 lines
2.5 KiB
JavaScript
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'use strict';
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// Serialises an async dispatch so that high-frequency callers cannot stack
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// up overlapping invocations. Intermediate values are dropped — only the
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// most recent fire() during an in-flight dispatch is replayed afterwards.
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// Extracted from machineGroupControl's _dispatchInFlight + _delayedCall
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// pattern so MGC, pumpingStation, valveGroupControl etc. can share it.
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class LatestWinsGate {
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constructor(asyncDispatchFn, options = {}) {
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if (typeof asyncDispatchFn !== 'function') {
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throw new TypeError('LatestWinsGate requires an async dispatch function');
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}
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this._dispatch = asyncDispatchFn;
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this._logger = options.logger || null;
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this._inFlight = false;
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this._pending = null; // { value, ctx } | null
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this._drainResolvers = []; // resolved when idle again
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this.lastError = null;
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}
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// 0 = idle, 1 = running with no pending, 2 = running with pending.
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get size() {
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if (!this._inFlight) return 0;
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return this._pending ? 2 : 1;
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}
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// Never blocks the caller. If a dispatch is in flight, the latest
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// value is parked; older parked values are silently overwritten.
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fire(value, ctx) {
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if (this._inFlight) {
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this._pending = { value, ctx };
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return;
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}
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this._run(value, ctx);
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}
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drain() {
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if (!this._inFlight && !this._pending) return Promise.resolve();
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return new Promise((resolve) => { this._drainResolvers.push(resolve); });
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}
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_run(value, ctx) {
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this._inFlight = true;
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// Kick the dispatch on a microtask so fire() always returns
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// synchronously, even if _dispatch resolves immediately.
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Promise.resolve()
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.then(() => this._dispatch(value, ctx))
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.catch((err) => {
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this.lastError = err;
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if (this._logger && typeof this._logger.error === 'function') {
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this._logger.error(err);
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}
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// Swallow: an error must not deadlock the gate.
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})
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.then(() => this._afterDispatch());
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}
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_afterDispatch() {
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this._inFlight = false;
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if (this._pending) {
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const { value, ctx } = this._pending;
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this._pending = null;
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this._run(value, ctx);
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return;
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}
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// Idle — release any drain() waiters.
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const waiters = this._drainResolvers;
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this._drainResolvers = [];
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for (const r of waiters) r();
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}
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}
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module.exports = LatestWinsGate;
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