67 lines
2.1 KiB
JavaScript
67 lines
2.1 KiB
JavaScript
"use strict";
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// rawAsap provides everything we need except exception management.
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var rawAsap = require("./raw");
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// RawTasks are recycled to reduce GC churn.
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var freeTasks = [];
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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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var pendingErrors = [];
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var requestErrorThrow = rawAsap.makeRequestCallFromTimer(throwFirstError);
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function throwFirstError() {
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if (pendingErrors.length) {
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throw pendingErrors.shift();
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}
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}
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/**
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* Calls a task as soon as possible after returning, in its own event, with priority
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* over other events like animation, reflow, and repaint. An error thrown from an
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* event will not interrupt, nor even substantially slow down the processing of
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* other events, but will be rather postponed to a lower priority event.
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* @param {{call}} task A callable object, typically a function that takes no
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* arguments.
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*/
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module.exports = asap;
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function asap(task) {
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var rawTask;
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if (freeTasks.length) {
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rawTask = freeTasks.pop();
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} else {
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rawTask = new RawTask();
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}
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rawTask.task = task;
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rawAsap(rawTask);
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}
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// We wrap tasks with recyclable task objects. A task object implements
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// `call`, just like a function.
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function RawTask() {
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this.task = null;
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}
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// The sole purpose of wrapping the task is to catch the exception and recycle
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// the task object after its single use.
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RawTask.prototype.call = function () {
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try {
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this.task.call();
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} catch (error) {
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if (asap.onerror) {
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// This hook exists purely for testing purposes.
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// Its name will be periodically randomized to break any code that
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// depends on its existence.
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asap.onerror(error);
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} else {
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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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pendingErrors.push(error);
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requestErrorThrow();
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}
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} finally {
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this.task = null;
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freeTasks[freeTasks.length] = this;
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}
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};
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