- 作者:陳大魚頭
- 首發地址: https://github.com/KRISACHAN/ying-study/issues
- 說明:魚頭的學習記錄
正文
在網上看到這麼一道題:
這道題跟魚頭這篇記錄『什麼是時間分片(Time Slicing)?』有點相似,但不同的是這次是限制異步併發的數量。
所以話不多說,我們先來康康實現
首先我們來實現一個分割數組的函數~
const group = (list = [], max = 0) => {
if (!list.length) {
return list
}
let results = []
for (let i = 0, len = list.length; i < len; i += max) {
results.push(list.slice(i, i + max))
}
return results
}
這裏就是根據指定的併發數量來分割數組。主要就是for
+ slice
,這沒啥好說的
接下來我們再來一個用async
+ await
實現的請求集合封裝。
我們通Promise.allSettled
去執行每一組的請求集合。
Promise.allSettled
是一個新的API,跟Promise.all
差不多的用法,也是接受的數組,不過不同的是Promise.allSettled
會等所有任務結束之後纔會返回結果,而Promise.all
只要有一個reject
就會返回結果。
const requestHandler = async (
groupedUrl = [],
callback = () => { }
) => {
if (!groupedUrl.length) {
callback()
return groupedUrl
}
const newGroupedUrl = groupedUrl.map(fn => fn())
const resultsMapper = (results) => results.map(callback)
const data = await Promise.allSettled(newGroupedUrl).then(resultsMapper)
return data;
}
接下來就是主函數
const sendRequest = async (
urls = [],
max = 0,
callback = () => { }
) => {
if (!urls.length) {
return urls
}
const groupedUrls = group(urls, max)
const results = []
console.log('start !')
for (let groupedUrl of groupedUrls) {
try {
const result = await requestHandler(groupedUrl, callback)
results.push(result)
console.log('go')
} catch { }
}
console.log('done !')
return results
}
這裏就是利用了for
+ async
+ await
來限制併發。等每次併發任務結果出來之後再執行下一次的任務。
我們執行下栗子:
const p1 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, 'p1'))
const p2 = () => Promise.resolve(2)
const p3 = () => new Promise((resolve, reject) => setTimeout(resolve, 2000, 'p3'))
const p4 = () => Promise.resolve(4)
const p5 = () => new Promise((resolve, reject) => setTimeout(reject, 2000, 'p5'))
const p6 = () => Promise.resolve(6)
const p7 = () => new Promise((resolve, reject) => setTimeout(resolve, 1000, 'p7'))
const p8 = () => Promise.resolve(8)
const p9 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, 'p9'))
const p10 = () => Promise.resolve(10)
const p11 = () => new Promise((resolve, reject) => setTimeout(resolve, 2000, 'p10'))
const p12 = () => Promise.resolve(12)
const p13 = () => new Promise((resolve, reject) => setTimeout(reject, 1000, 'p11'))
const p14 = () => Promise.resolve(14)
const ps = [p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12, p13, p14]
sendRequest(ps, 3, ({reason, value}) => {
console.log(reason || value)
})
OK,我們看到結果是如我們所願的
後記
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