创建“运行循环”的最佳解决方案在JavaScript中

问题描述

事实证明，如果您希望应用程序响应外部/异步事件，则阻止它成为创建运行循环的可行解决方案。

So it turns out the while loop blocks the event loop in JavaScript, which prevents it from being a viable solution to creating a run loop if you want your application to respond to external / async events.

我的问题是，使用什么技术让运行循环为无限/常数但仍然具有高性能和不阻止事件循环。

My question is, what techniques are used to have a "run loop" be infinite / constant but still have high performance and not block the event loop.

我跑了一个快速测试，看的表现，而， setTimeout （fn，0）（浏览器）， setImmediate（fn）（node.js）。

I ran a quick test to see the performance of while, setTimeout(fn, 0) (browser), and setImmediate(fn) (node.js).

var x = 1000
var isNode = typeof window == 'undefined'

function a() {
  var start = (new Date()).getTime()
  var q = 0

  function next() {
    q++
    if (q < x) {
      if (isNode) {
        setImmediate(next)
      } else {
        setTimeout(next, 0)
      }
    } else {
      var end = (new Date).getTime()
      console.log('a', end - start)
    }
  }

  next()
}

function b() {
  var start = (new Date()).getTime()
  var q = 0

  while (q < x) {
    q++
  }

  var end = (new Date).getTime()
  console.log('b', end - start)
}

a()
b()

节点。 js：

a = 20
b = 0

浏览器：

a = 5039
b = 0

没有办法做一个无限循环，就像做一个while循环一样高效在JavaScript中。 setImmediate 比 setTimeout 快得多，但它仍然比基本的while循环慢很多。

Is there not a way to do an "infinite while loop" that is as performant as doing a while loop in JavaScript. setImmediate is much faster than setTimeout, but it's still a lot slower than the basic while loop.

推荐答案

这样的事情可行：

var THRESHOLDCOUNT = 10000
var THRESHOLDTIME = 15

function loop(fn) {
  var start = Date.now()
  var changed = false
  var x = 0

  while (!changed) {
    while (x < THRESHOLDCOUNT) {
      x++
      fn()
    }

    var end = Date.now()
    changed = end - start > THRESHOLDTIME
  }

  // make room for external events.
  setImmediate(loop)
}

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