102 lines
4.0 KiB
JavaScript
102 lines
4.0 KiB
JavaScript
"use strict";
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var domain; // The domain module is executed on demand
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var hasSetImmediate = typeof setImmediate === "function";
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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 network IO events in Node.js.
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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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module.exports = rawAsap;
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function rawAsap(task) {
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if (!queue.length) {
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requestFlush();
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flushing = true;
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}
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// Avoids a function call
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queue[queue.length] = task;
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}
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var queue = [];
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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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var flushing = false;
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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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var 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 excaustion, the task queue will periodically
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// truncate already-completed tasks.
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var capacity = 1024;
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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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function flush() {
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while (index < queue.length) {
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var currentIndex = 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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index = index + 1;
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queue[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 (index > 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 (var scan = 0, newLength = queue.length - index; scan < newLength; scan++) {
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queue[scan] = queue[scan + index];
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}
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queue.length -= index;
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index = 0;
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}
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}
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queue.length = 0;
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index = 0;
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flushing = false;
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}
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rawAsap.requestFlush = requestFlush;
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function requestFlush() {
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// Ensure flushing is not bound to any domain.
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// It is not sufficient to exit the domain, because domains exist on a stack.
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// To execute code outside of any domain, the following dance is necessary.
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var parentDomain = process.domain;
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if (parentDomain) {
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if (!domain) {
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// Lazy execute the domain module.
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// Only employed if the user elects to use domains.
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domain = require("domain");
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}
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domain.active = process.domain = null;
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}
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// `setImmediate` is slower that `process.nextTick`, but `process.nextTick`
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// cannot handle recursion.
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// `requestFlush` will only be called recursively from `asap.js`, to resume
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// flushing after an error is thrown into a domain.
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// Conveniently, `setImmediate` was introduced in the same version
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// `process.nextTick` started throwing recursion errors.
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if (flushing && hasSetImmediate) {
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setImmediate(flush);
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} else {
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process.nextTick(flush);
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}
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if (parentDomain) {
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domain.active = process.domain = parentDomain;
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}
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}
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