166 lines
6.9 KiB
TypeScript
166 lines
6.9 KiB
TypeScript
/* eslint-disable no-restricted-globals, @typescript-eslint/ban-ts-comment, @typescript-eslint/no-unused-vars, @typescript-eslint/no-non-null-assertion */
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import { makeRequestCall, makeRequestCallFromTimer } from './makeRequestCall.js'
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import type { Task } from './types.js'
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export class AsapQueue {
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private queue: Task[] = []
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// We queue errors to ensure they are thrown in right order (FIFO).
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// Array-as-queue is good enough here, since we are just dealing with exceptions.
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private pendingErrors: any[] = []
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// Once a flush has been requested, no further calls to `requestFlush` are
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// necessary until the next `flush` completes.
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// @ts-ignore
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private flushing = false
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// `requestFlush` is an implementation-specific method that attempts to kick
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// off a `flush` event as quickly as possible. `flush` will attempt to exhaust
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// the event queue before yielding to the browser's own event loop.
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private requestFlush: () => void
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private requestErrorThrow: () => void
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// The position of the next task to execute in the task queue. This is
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// preserved between calls to `flush` so that it can be resumed if
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// a task throws an exception.
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private index = 0
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// If a task schedules additional tasks recursively, the task queue can grow
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// unbounded. To prevent memory exhaustion, the task queue will periodically
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// truncate already-completed tasks.
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private capacity = 1024
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public constructor() {
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// `requestFlush` requests that the high priority event queue be flushed as
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// soon as possible.
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// This is useful to prevent an error thrown in a task from stalling the event
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// queue if the exception handled by Node.js’s
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// `process.on("uncaughtException")` or by a domain.
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// `requestFlush` is implemented using a strategy based on data collected from
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// every available SauceLabs Selenium web driver worker at time of writing.
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// https://docs.google.com/spreadsheets/d/1mG-5UYGup5qxGdEMWkhP6BWCz053NUb2E1QoUTU16uA/edit#gid=783724593
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this.requestFlush = makeRequestCall(this.flush)
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this.requestErrorThrow = makeRequestCallFromTimer(() => {
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// Throw first error
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if (this.pendingErrors.length) {
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throw this.pendingErrors.shift()
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}
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})
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}
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// Use the fastest means possible to execute a task in its own turn, with
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// priority over other events including IO, animation, reflow, and redraw
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// events in browsers.
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//
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// An exception thrown by a task will permanently interrupt the processing of
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// subsequent tasks. The higher level `asap` function ensures that if an
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// exception is thrown by a task, that the task queue will continue flushing as
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// soon as possible, but if you use `rawAsap` directly, you are responsible to
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// either ensure that no exceptions are thrown from your task, or to manually
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// call `rawAsap.requestFlush` if an exception is thrown.
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public enqueueTask(task: Task): void {
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const { queue: q, requestFlush } = this
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if (!q.length) {
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requestFlush()
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this.flushing = true
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}
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// Equivalent to push, but avoids a function call.
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q[q.length] = task
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}
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// The flush function processes all tasks that have been scheduled with
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// `rawAsap` unless and until one of those tasks throws an exception.
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// If a task throws an exception, `flush` ensures that its state will remain
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// consistent and will resume where it left off when called again.
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// However, `flush` does not make any arrangements to be called again if an
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// exception is thrown.
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private flush = () => {
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const { queue: q } = this
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while (this.index < q.length) {
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const currentIndex = this.index
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// Advance the index before calling the task. This ensures that we will
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// begin flushing on the next task the task throws an error.
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this.index++
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q[currentIndex]!.call()
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// Prevent leaking memory for long chains of recursive calls to `asap`.
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// If we call `asap` within tasks scheduled by `asap`, the queue will
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// grow, but to avoid an O(n) walk for every task we execute, we don't
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// shift tasks off the queue after they have been executed.
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// Instead, we periodically shift 1024 tasks off the queue.
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if (this.index > this.capacity) {
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// Manually shift all values starting at the index back to the
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// beginning of the queue.
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for (
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let scan = 0, newLength = q.length - this.index;
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scan < newLength;
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scan++
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) {
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q[scan] = q[scan + this.index]!
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}
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q.length -= this.index
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this.index = 0
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}
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}
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q.length = 0
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this.index = 0
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this.flushing = false
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}
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// In a web browser, exceptions are not fatal. However, to avoid
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// slowing down the queue of pending tasks, we rethrow the error in a
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// lower priority turn.
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public registerPendingError = (err: any) => {
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this.pendingErrors.push(err)
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this.requestErrorThrow()
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}
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}
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// The message channel technique was discovered by Malte Ubl and was the
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// original foundation for this library.
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// http://www.nonblocking.io/2011/06/windownexttick.html
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// Safari 6.0.5 (at least) intermittently fails to create message ports on a
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// page's first load. Thankfully, this version of Safari supports
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// MutationObservers, so we don't need to fall back in that case.
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// function makeRequestCallFromMessageChannel(callback) {
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// var channel = new MessageChannel();
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// channel.port1.onmessage = callback;
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// return function requestCall() {
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// channel.port2.postMessage(0);
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// };
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// }
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// For reasons explained above, we are also unable to use `setImmediate`
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// under any circumstances.
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// Even if we were, there is another bug in Internet Explorer 10.
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// It is not sufficient to assign `setImmediate` to `requestFlush` because
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// `setImmediate` must be called *by name* and therefore must be wrapped in a
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// closure.
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// Never forget.
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// function makeRequestCallFromSetImmediate(callback) {
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// return function requestCall() {
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// setImmediate(callback);
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// };
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// }
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// Safari 6.0 has a problem where timers will get lost while the user is
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// scrolling. This problem does not impact ASAP because Safari 6.0 supports
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// mutation observers, so that implementation is used instead.
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// However, if we ever elect to use timers in Safari, the prevalent work-around
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// is to add a scroll event listener that calls for a flush.
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// `setTimeout` does not call the passed callback if the delay is less than
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// approximately 7 in web workers in Firefox 8 through 18, and sometimes not
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// even then.
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// This is for `asap.js` only.
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// Its name will be periodically randomized to break any code that depends on
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// // its existence.
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// rawAsap.makeRequestCallFromTimer = makeRequestCallFromTimer
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// ASAP was originally a nextTick shim included in Q. This was factored out
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// into this ASAP package. It was later adapted to RSVP which made further
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// amendments. These decisions, particularly to marginalize MessageChannel and
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// to capture the MutationObserver implementation in a closure, were integrated
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// back into ASAP proper.
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// https://github.com/tildeio/rsvp.js/blob/cddf7232546a9cf858524b75cde6f9edf72620a7/lib/rsvp/asap.js
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