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