ce4c83ff
 wxy
初始提交
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"use strict";
// rawAsap provides everything we need except exception management.
var rawAsap = require("./raw");
// RawTasks are recycled to reduce GC churn.
var freeTasks = [];
// We queue errors to ensure they are thrown in right order (FIFO).
// Array-as-queue is good enough here, since we are just dealing with exceptions.
var pendingErrors = [];
var requestErrorThrow = rawAsap.makeRequestCallFromTimer(throwFirstError);
function throwFirstError() {
if (pendingErrors.length) {
throw pendingErrors.shift();
}
}
/**
* Calls a task as soon as possible after returning, in its own event, with priority
* over other events like animation, reflow, and repaint. An error thrown from an
* event will not interrupt, nor even substantially slow down the processing of
* other events, but will be rather postponed to a lower priority event.
* @param {{call}} task A callable object, typically a function that takes no
* arguments.
*/
module.exports = asap;
function asap(task) {
var rawTask;
if (freeTasks.length) {
rawTask = freeTasks.pop();
} else {
rawTask = new RawTask();
}
rawTask.task = task;
rawAsap(rawTask);
}
// We wrap tasks with recyclable task objects. A task object implements
// `call`, just like a function.
function RawTask() {
this.task = null;
}
// The sole purpose of wrapping the task is to catch the exception and recycle
// the task object after its single use.
RawTask.prototype.call = function () {
try {
this.task.call();
} catch (error) {
if (asap.onerror) {
// This hook exists purely for testing purposes.
// Its name will be periodically randomized to break any code that
// depends on its existence.
asap.onerror(error);
} else {
// In a web browser, exceptions are not fatal. However, to avoid
// slowing down the queue of pending tasks, we rethrow the error in a
// lower priority turn.
pendingErrors.push(error);
requestErrorThrow();
}
} finally {
this.task = null;
freeTasks[freeTasks.length] = this;
}
};
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