import { Action } from './Action';
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import { SchedulerAction } from '../types';
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import { Subscription } from '../Subscription';
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import { AsyncScheduler } from './AsyncScheduler';
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import { intervalProvider } from './intervalProvider';
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import { arrRemove } from '../util/arrRemove';
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import { TimerHandle } from './timerHandle';
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export class AsyncAction<T> extends Action<T> {
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public id: TimerHandle | undefined;
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public state?: T;
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// @ts-ignore: Property has no initializer and is not definitely assigned
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public delay: number;
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protected pending: boolean = false;
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constructor(protected scheduler: AsyncScheduler, protected work: (this: SchedulerAction<T>, state?: T) => void) {
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super(scheduler, work);
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}
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public schedule(state?: T, delay: number = 0): Subscription {
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if (this.closed) {
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return this;
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}
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// Always replace the current state with the new state.
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this.state = state;
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const id = this.id;
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const scheduler = this.scheduler;
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//
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// Important implementation note:
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//
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// Actions only execute once by default, unless rescheduled from within the
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// scheduled callback. This allows us to implement single and repeat
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// actions via the same code path, without adding API surface area, as well
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// as mimic traditional recursion but across asynchronous boundaries.
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//
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// However, JS runtimes and timers distinguish between intervals achieved by
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// serial `setTimeout` calls vs. a single `setInterval` call. An interval of
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// serial `setTimeout` calls can be individually delayed, which delays
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// scheduling the next `setTimeout`, and so on. `setInterval` attempts to
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// guarantee the interval callback will be invoked more precisely to the
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// interval period, regardless of load.
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//
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// Therefore, we use `setInterval` to schedule single and repeat actions.
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// If the action reschedules itself with the same delay, the interval is not
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// canceled. If the action doesn't reschedule, or reschedules with a
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// different delay, the interval will be canceled after scheduled callback
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// execution.
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//
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if (id != null) {
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this.id = this.recycleAsyncId(scheduler, id, delay);
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}
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// Set the pending flag indicating that this action has been scheduled, or
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// has recursively rescheduled itself.
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this.pending = true;
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this.delay = delay;
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// If this action has already an async Id, don't request a new one.
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this.id = this.id ?? this.requestAsyncId(scheduler, this.id, delay);
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return this;
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}
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protected requestAsyncId(scheduler: AsyncScheduler, _id?: TimerHandle, delay: number = 0): TimerHandle {
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return intervalProvider.setInterval(scheduler.flush.bind(scheduler, this), delay);
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}
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protected recycleAsyncId(_scheduler: AsyncScheduler, id?: TimerHandle, delay: number | null = 0): TimerHandle | undefined {
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// If this action is rescheduled with the same delay time, don't clear the interval id.
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if (delay != null && this.delay === delay && this.pending === false) {
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return id;
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}
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// Otherwise, if the action's delay time is different from the current delay,
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// or the action has been rescheduled before it's executed, clear the interval id
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if (id != null) {
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intervalProvider.clearInterval(id);
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}
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return undefined;
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}
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/**
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* Immediately executes this action and the `work` it contains.
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* @return {any}
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*/
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public execute(state: T, delay: number): any {
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if (this.closed) {
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return new Error('executing a cancelled action');
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}
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this.pending = false;
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const error = this._execute(state, delay);
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if (error) {
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return error;
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} else if (this.pending === false && this.id != null) {
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// Dequeue if the action didn't reschedule itself. Don't call
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// unsubscribe(), because the action could reschedule later.
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// For example:
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// ```
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// scheduler.schedule(function doWork(counter) {
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// /* ... I'm a busy worker bee ... */
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// var originalAction = this;
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// /* wait 100ms before rescheduling the action */
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// setTimeout(function () {
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// originalAction.schedule(counter + 1);
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// }, 100);
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// }, 1000);
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// ```
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this.id = this.recycleAsyncId(this.scheduler, this.id, null);
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}
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}
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protected _execute(state: T, _delay: number): any {
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let errored: boolean = false;
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let errorValue: any;
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try {
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this.work(state);
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} catch (e) {
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errored = true;
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// HACK: Since code elsewhere is relying on the "truthiness" of the
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// return here, we can't have it return "" or 0 or false.
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// TODO: Clean this up when we refactor schedulers mid-version-8 or so.
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errorValue = e ? e : new Error('Scheduled action threw falsy error');
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}
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if (errored) {
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this.unsubscribe();
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return errorValue;
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}
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}
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unsubscribe() {
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if (!this.closed) {
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const { id, scheduler } = this;
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const { actions } = scheduler;
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this.work = this.state = this.scheduler = null!;
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this.pending = false;
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arrRemove(actions, this);
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if (id != null) {
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this.id = this.recycleAsyncId(scheduler, id, null);
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}
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this.delay = null!;
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super.unsubscribe();
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}
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}
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}
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