我应该使用process.nextTick或setImmediate进行异步迭代吗？ [英] Should I use process.nextTick or setImmediate for asynchronous iteration?

问题描述

我正在开发一个JavaScript库，其中包括地图/减少可以异步迭代的序列上的函数。

I'm working on a JavaScript library that provides, among other things, map/reduce functions on sequences that can be iterated asynchronously.

A 建议对于Node.js，我应该使用 process.nextTick 来尽可能快地进行异步迭代。 （该库目前在所有环境中都使用 setTimeout ，我知道这是次优的。）我对Node很缺乏经验，所以我正在阅读这是怎么回事方法是有效的，我不清楚它是否是一个好的选择。

A helpful soul on GitHub suggested that for Node.js, I should use process.nextTick to make asynchronous iterations as fast as possible. (The library currently uses setTimeout in all environments, which I do understand is suboptimal.) I'm pretty inexperienced when it comes to Node, so I was reading up on how this method works and it isn't clear to me whether it's a good choice or not.

根据关于SO的另一个问题的答案，在这种情况下使用 setImmediate 似乎更有意义 nextTick 显然是等待提前挂起的I / O事件，这对我来说似乎不好。

According to the answer to another question on SO, it seems that it would probably make more sense to use setImmediate in this case as nextTick apparently jumps ahead of pending I/O events, which seems bad to me.

中的一些评论似乎证实了这一点。官方节点v0.10.0公告：

在v0.10中， nextTick 处理程序在每次从C ++
调用JavaScript后立即运行。这意味着，如果您的JavaScript代码调用
process.nextTick ，那么一旦代码运行
即可完成回调，但在回到事件循环之前。

In v0.10, nextTick handlers are run right after each call from C++ into JavaScript. That means that, if your JavaScript code calls process.nextTick, then the callback will fire as soon as the code runs to completion, but before going back to the event loop.

所以我是对的，并且异步迭代序列应该完成使用 setImmediate ？或者 nextTick 在这里是一个更好的选择？ （在任何一种情况下，一个明确的解释为什么将非常感激。）

So am I right, and iterating over sequences asynchronously should be done with setImmediate? Or would nextTick be a better choice here? (In either case, a clear explanation why would be much appreciated.)

推荐答案

一些注意事项：

我首先要对setImmediate的扩展速度比 process.nextTick 做更严格的基准测试。如果它没有（太慢），我会立即去 setImmediate ，因为这不会使事件循环挨饿。

I'd first do serious benchmarks to what extend setImmediate is slower than process.nextTick. If it's not (much) slower, I'd go for setImmediate straight away since that won't starve the event loop.

在节点0.10中有一个硬限制（1000，请参阅节点。 js docs ）你可以递归调用nextTick多少次，所以你应该防止在任何情况下发生这种情况。您需要在迭代之前选择策略，或者能够在迭代期间更改策略（同时检查当前迭代计数）。

In node 0.10 there's a hard limit (1000, see node.js docs) to how many times you can recursively call nextTick, so you should prevent that from happening in any case. You either need to choose a strategy before iteration, or be able to change strategy during iteration (while checking for current iteration count).

如果选择process.nextTick以获得性能原因，你可能想要设置一个可配置的硬限制，连续多少次 process.nextTick ，然后切换到 setImmediate 。我没有在nodejs上有严重工作量的经验，但我认为如果你的库使他们的I / O不稳定，人们就不会喜欢它。

If you choose process.nextTick for performance reasons, you might want to set a configurable hard limit for how many times it would do process.nextTick in a row, and else switch to setImmediate. I don't have experience with serious work loads on nodejs, but I do think people are not gonna like it if your library makes their I/O choppy.

setImmediate will肯定是最安全的，总而言之。

setImmediate would certainly be safest, all in all.

至于浏览器：
我没有研究过您的图书馆，但因为您实际上是来自 setTimeout ，您可以通过 window.postMessage 帮助您了解新的延迟技术，什么不是。有一个很好的小型库，名为 next-tick （但语义不同于节点next-tick！）并且有一个<一个href =https://github.com/NobleJS/setImmediate>用于setImmediate 的跨浏览器填充程序，这是相当重的因为1）它需要实现setImmediate规范（包括取消预定的能力）任务）和2）它有更广泛的浏览器兼容性。

As for the browser: I haven't studied your library, but since you are actually coming from setTimeout, you may be helped learning about the new breed of delay techniques via window.postMessage and what not. There's a nice and small library called next-tick (but with different semantics than node next-tick!) and there's a cross-browser shim for setImmediate, which is quite a bit heavier because 1) it needs to implement the setImmediate spec (including ability to cancel scheduled tasks) and 2) it has much wider browser compatibility.

看看这个异步排序演示将setImmediate（shim）与setTimeout进行比较。

Check out this async sorting demo comparing setImmediate (shim) to setTimeout.

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