08-27-周三_17-09-29

node_modules/asap/README.md

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+
+# ASAP
+
+This `asap` CommonJS package contains a single `asap` module that
+exports a single `asap` function that executes a function **as soon as
+possible**.
+
+```javascript
+asap(function () {
+    // ...
+});
+```
+
+More formally, ASAP provides a fast event queue that will execute tasks
+until it is empty before yielding to the JavaScript engine's underlying
+event-loop.  When the event queue becomes non-empty, ASAP schedules a
+flush event, preferring for that event to occur before the JavaScript
+engine has an opportunity to perform IO tasks or rendering, thus making
+the first task and subsequent tasks semantically indistinguishable.
+ASAP uses a variety of techniques to preserve this invariant on
+different versions of browsers and NodeJS.
+
+By design, ASAP can starve the event loop on the theory that, if there
+is enough work to be done synchronously, albeit in separate events, long
+enough to starve input or output, it is a strong indicator that the
+program needs to push back on scheduling more work.
+
+Take care.  ASAP can sustain infinite recursive calls indefinitely
+without warning.  This is behaviorally equivalent to an infinite loop.
+It will not halt from a stack overflow, but it *will* chew through
+memory (which is an oddity I cannot explain at this time).  Just as with
+infinite loops, you can monitor a Node process for this behavior with a
+heart-beat signal.  As with infinite loops, a very small amount of
+caution goes a long way to avoiding problems.
+
+```javascript
+function loop() {
+    asap(loop);
+}
+loop();
+```
+
+ASAP is distinct from `setImmediate` in that it does not suffer the
+overhead of returning a handle and being possible to cancel.  For a
+`setImmediate` shim, consider [setImmediate][].
+
+[setImmediate]: https://github.com/noblejs/setimmediate
+
+If a task throws an exception, it will not interrupt the flushing of
+high-priority tasks.  The exception will be postponed to a later,
+low-priority event to avoid slow-downs, when the underlying JavaScript
+engine will treat it as it does any unhandled exception.
+
+## Heritage
+
+ASAP has been factored out of the [Q][] asynchronous promise library.
+It originally had a naïve implementation in terms of `setTimeout`, but
+[Malte Ubl][NonBlocking] provided an insight that `postMessage` might be
+useful for creating a high-priority, no-delay event dispatch hack.
+Since then, Internet Explorer proposed and implemented `setImmediate`.
+Robert Kratić began contributing to Q by measuring the performance of
+the internal implementation of `asap`, paying particular attention to
+error recovery.  Domenic, Robert, and I collectively settled on the
+current strategy of unrolling the high-priority event queue internally
+regardless of what strategy we used to dispatch the potentially
+lower-priority flush event.  Domenic went on to make ASAP cooperate with
+NodeJS domains.
+
+[Q]: https://github.com/kriskowal/q
+[NonBlocking]: http://www.nonblocking.io/2011/06/windownexttick.html
+
+For further reading, Nicholas Zakas provided a thorough article on [The
+Case for setImmediate][NCZ].
+
+[NCZ]: http://www.nczonline.net/blog/2013/07/09/the-case-for-setimmediate/
+
+## License
+
+Copyright 2009-2013 by Contributors
+MIT License (enclosed)
+