@reactivex/rxjs/dist/es6/scheduler/FutureAction.js

Reactive Extensions for modern JavaScript

import { root } from '../util/root';
import { Subscription } from '../Subscription';
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
export class FutureAction extends Subscription {
    constructor(scheduler, work) {
        super();
        this.scheduler = scheduler;
        this.work = work;
        this.pending = false;
    }
    execute() {
        if (this.isUnsubscribed) {
            this.error = new Error('executing a cancelled action');
        }
        else {
            try {
                this.work(this.state);
            }
            catch (e) {
                this.unsubscribe();
                this.error = e;
            }
        }
    }
    schedule(state, delay = 0) {
        if (this.isUnsubscribed) {
            return this;
        }
        return this._schedule(state, delay);
    }
    _schedule(state, delay = 0) {
        // Always replace the current state with the new state.
        this.state = state;
        // Set the pending flag indicating that this action has been scheduled, or
        // has recursively rescheduled itself.
        this.pending = true;
        const id = this.id;
        // If this action has an intervalID and the specified delay matches the
        // delay we used to create the intervalID, don't call `setInterval` again.
        if (id != null && this.delay === delay) {
            return this;
        }
        this.delay = delay;
        // If this action has an intervalID, but was rescheduled with a different
        // `delay` time, cancel the current intervalID and call `setInterval` with
        // the new `delay` time.
        if (id != null) {
            this.id = null;
            root.clearInterval(id);
        }
        //
        // Important implementation note:
        //
        // By default, FutureAction only executes once. However, Actions have the
        // ability to be rescheduled from within the scheduled callback (mimicking
        // recursion for asynchronous methods). This allows us to implement single
        // and repeated actions with the same code path without adding API surface
        // area, and implement tail-call optimization over asynchronous boundaries.
        //
        // However, JS runtimes make a distinction between intervals scheduled by
        // repeatedly calling `setTimeout` vs. a single `setInterval` call, with
        // the latter providing a better guarantee of precision.
        //
        // In order to accommodate both single and repeatedly rescheduled actions,
        // use `setInterval` here for both cases. By default, the interval will be
        // canceled after its first execution, or if the action schedules itself to
        // run again with a different `delay` time.
        //
        // If the action recursively schedules itself to run again with the same
        // `delay` time, the interval is not canceled, but allowed to loop again.
        // The check of whether the interval should be canceled or not is run every
        // time the interval is executed. The first time an action fails to
        // reschedule itself, the interval is canceled.
        //
        this.id = root.setInterval(() => {
            this.pending = false;
            const { id, scheduler } = this;
            scheduler.actions.push(this);
            scheduler.flush();
            //
            // Terminate this interval if the action didn't reschedule itself.
            // Don't call `this.unsubscribe()` here, because the action could be
            // rescheduled later. For example:
            //
            // ```
            // scheduler.schedule(function doWork(counter) {
            //   /* ... I'm a busy worker bee ... */
            //   var originalAction = this;
            //   /* wait 100ms before rescheduling this action again */
            //   setTimeout(function () {
            //     originalAction.schedule(counter + 1);
            //   }, 100);
            // }, 1000);
            // ```
            if (this.pending === false && id != null) {
                this.id = null;
                root.clearInterval(id);
            }
        }, delay);
        return this;
    }
    _unsubscribe() {
        this.pending = false;
        const { id, scheduler } = this;
        const { actions } = scheduler;
        const index = actions.indexOf(this);
        if (id != null) {
            this.id = null;
            root.clearInterval(id);
        }
        if (index !== -1) {
            actions.splice(index, 1);
        }
        this.work = null;
        this.state = null;
        this.scheduler = null;
    }
}
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