asap/asap.js

"use strict";

var rawAsap = require("./raw");
var freeTasks = [];

/**
 * Calls a task as soon as possible after returning, in its own event, with
 * priority over IO events. An exception thrown in a task can be handled by
 * `process.on("uncaughtException") or `domain.on("error")`, but will otherwise
 * crash the process. If the error is handled, all subsequent tasks will
 * resume.
 *
 * @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;
    rawTask.domain = process.domain;
    rawAsap(rawTask);
}

function RawTask() {
    this.task = null;
    this.domain = null;
}

RawTask.prototype.call = function () {
    if (this.domain) {
        this.domain.enter();
    }
    var threw = true;
    try {
        this.task.call();
        threw = false;
        // If the task throws an exception (presumably) Node.js restores the
        // domain stack for the next event.
        if (this.domain) {
            this.domain.exit();
        }
    } finally {
        // We use try/finally and a threw flag to avoid messing up stack traces
        // when we catch and release errors.
        if (threw) {
            // In Node.js, uncaught exceptions are considered fatal errors.
            // Re-throw them to interrupt flushing!
            // Ensure that flushing continues if an uncaught exception is
            // suppressed listening process.on("uncaughtException") or
            // domain.on("error").
            rawAsap.requestFlush();
        }
        // If the task threw an error, we do not want to exit the domain here.
        // Exiting the domain would prevent the domain from catching the error.
        this.task = null;
        this.domain = null;
        freeTasks.push(this);
    }
};