75 lines
2.7 KiB
JavaScript
75 lines
2.7 KiB
JavaScript
"use strict";
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/*
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* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
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* SPDX-License-Identifier: Apache-2.0.
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*/
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.newLiftedPromise = exports.makeSelfCleaningPromise = void 0;
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/**
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* A helper function that takes a promise and creates a wrapper promise that invokes a cleanup function when the inner
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* promise is completed for any reason. The primary use is to remove event listeners related to promise completion
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* when the promise actually completes. This allows us to keep the number of listeners on a CancelController bounded by
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* the number of incomplete promises associated with it. If we didn't clean up, the listener set would grow
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* without limit.
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*
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* For cancellation, this leads to an internal usage pattern that is strongly recommended:
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*
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* ```
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* async doSomethingCancellable(...) : Promise<...> {
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* removeListenerFunctor = undefined;
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*
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* innerPromise = new Promise(async (resolve, reject) => {
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* ...
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*
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* cancelListenerFunction = () => { clean up and reject innerPromise };
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* removeListenerFunctor = cancelController.addListener(cancelListenerFunction);
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*
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* ...
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* }
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*
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* return makeSelfCleaningPromise(innerPromise, removeListenerFunctor);
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* }
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* ```
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*
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* @param promise promise to wrap with automatic cleanup
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* @param cleaner cleaner function to invoke when the promise is completed
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*
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* @return a promise with matching result/err, that invokes the cleaner function on inner promise completion
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*/
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function makeSelfCleaningPromise(promise, cleaner) {
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if (!cleaner) {
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return promise;
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}
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return promise.finally(() => { cleaner(); });
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}
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exports.makeSelfCleaningPromise = makeSelfCleaningPromise;
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/**
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* Factory function to create a new LiftedPromise
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*
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* @param promiseBody optional body function to invoke as part of promise creation
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*
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* @return a promise whose resolve and reject methods have been lifted out of the internal body function and made
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* available to external actors
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*/
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function newLiftedPromise(promiseBody) {
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let localResolve = undefined;
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let localReject = undefined;
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let promise = new Promise((resolve, reject) => {
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localResolve = resolve;
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localReject = reject;
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});
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if (!localResolve || !localReject) {
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// should never happen
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throw new Error("Failed to bind resolve and reject when making lifted promise");
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}
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if (promiseBody) {
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promiseBody(localResolve, localReject);
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}
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return {
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promise: promise,
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resolve: localResolve,
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reject: localReject
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};
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}
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exports.newLiftedPromise = newLiftedPromise;
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//# sourceMappingURL=promise.js.map
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