99 lines
3.8 KiB
JavaScript
99 lines
3.8 KiB
JavaScript
/******************************************************************************
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* Copyright 2021 TypeFox GmbH
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* This program and the accompanying materials are made available under the
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* terms of the MIT License, which is available in the project root.
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******************************************************************************/
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import { CancellationToken, CancellationTokenSource } from '../utils/cancellation.js';
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/**
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* Delays the execution of the current code to the next tick of the event loop.
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* Don't call this method directly in a tight loop to prevent too many promises from being created.
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*/
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export function delayNextTick() {
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return new Promise(resolve => {
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// In case we are running in a non-node environment, `setImmediate` isn't available.
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// Using `setTimeout` of the browser API accomplishes the same result.
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if (typeof setImmediate === 'undefined') {
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setTimeout(resolve, 0);
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}
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else {
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setImmediate(resolve);
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}
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});
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}
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let lastTick = 0;
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let globalInterruptionPeriod = 10;
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/**
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* Reset the global interruption period and create a cancellation token source.
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*/
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export function startCancelableOperation() {
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lastTick = performance.now();
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return new CancellationTokenSource();
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}
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/**
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* Change the period duration for `interruptAndCheck` to the given number of milliseconds.
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* The default value is 10ms.
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*/
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export function setInterruptionPeriod(period) {
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globalInterruptionPeriod = period;
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}
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/**
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* This symbol may be thrown in an asynchronous context by any Langium service that receives
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* a `CancellationToken`. This means that the promise returned by such a service is rejected with
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* this symbol as rejection reason.
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*/
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export const OperationCancelled = Symbol('OperationCancelled');
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/**
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* Use this in a `catch` block to check whether the thrown object indicates that the operation
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* has been cancelled.
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*/
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export function isOperationCancelled(err) {
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return err === OperationCancelled;
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}
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/**
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* This function does two things:
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* 1. Check the elapsed time since the last call to this function or to `startCancelableOperation`. If the predefined
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* period (configured with `setInterruptionPeriod`) is exceeded, execution is delayed with `delayNextTick`.
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* 2. If the predefined period is not met yet or execution is resumed after an interruption, the given cancellation
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* token is checked, and if cancellation is requested, `OperationCanceled` is thrown.
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*
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* All services in Langium that receive a `CancellationToken` may potentially call this function, so the
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* `CancellationToken` must be caught (with an `async` try-catch block or a `catch` callback attached to
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* the promise) to avoid that event being exposed as an error.
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*/
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export async function interruptAndCheck(token) {
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if (token === CancellationToken.None) {
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// Early exit in case cancellation was disabled by the caller
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return;
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}
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const current = performance.now();
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if (current - lastTick >= globalInterruptionPeriod) {
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lastTick = current;
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await delayNextTick();
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// prevent calling delayNextTick every iteration of loop
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// where delayNextTick takes up the majority or all of the
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// globalInterruptionPeriod itself
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lastTick = performance.now();
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}
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if (token.isCancellationRequested) {
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throw OperationCancelled;
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}
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}
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/**
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* Simple implementation of the deferred pattern.
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* An object that exposes a promise and functions to resolve and reject it.
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*/
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export class Deferred {
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constructor() {
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this.promise = new Promise((resolve, reject) => {
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this.resolve = (arg) => {
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resolve(arg);
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return this;
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};
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this.reject = (err) => {
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reject(err);
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return this;
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};
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});
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}
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}
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//# sourceMappingURL=promise-utils.js.map
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