限制正在運行的承諾的並發性

Question

我正在尋找一個 Promise 函數包裝器，它可以在給定的 Promise 運行時限制/限制，以便在給定的時間只有一組該 Promise 正在運行。

在下面的例子中， delayPromise不應該同時運行，它們都應該按照先到先得的順序一次運行一個。

import Promise from 'bluebird'

function _delayPromise (seconds, str) {
  console.log(str)
  return Promise.delay(seconds)
}

let delayPromise = limitConcurrency(_delayPromise, 1)

async function a() {
  await delayPromise(100, "a:a")
  await delayPromise(100, "a:b")
  await delayPromise(100, "a:c")
}

async function b() {
  await delayPromise(100, "b:a")
  await delayPromise(100, "b:b")
  await delayPromise(100, "b:c")
}

a().then(() => console.log('done'))

b().then(() => console.log('done'))

關於如何設置這樣的隊列的任何想法？

我有一個很棒的Benjamin Gruenbaum的“去抖動”功能。 我需要修改它以根據它自己的執行而不是延遲來限制承諾。

export function promiseDebounce (fn, delay, count) {
  let working = 0
  let queue = []
  function work () {
    if ((queue.length === 0) || (working === count)) return
    working++
    Promise.delay(delay).tap(function () { working-- }).then(work)
    var next = queue.shift()
    next[2](fn.apply(next[0], next[1]))
  }
  return function debounced () {
    var args = arguments
    return new Promise(function (resolve) {
      queue.push([this, args, resolve])
      if (working < count) work()
    }.bind(this))
  }
}

Answer 1

我不認為有任何庫可以做到這一點，但實現自己實際上很簡單：

function queue(fn) { // limitConcurrency(fn, 1)
    var q = Promise.resolve();
    return function(x) {
        var p = q.then(function() {
            return fn(x);
        });
        q = p.reflect();
        return p;
    };
}

對於多個並發請求，它變得有點棘手，但也可以完成。

function limitConcurrency(fn, n) {
    if (n == 1) return queue(fn); // optimisation
    var q = null;
    var active = [];
    function next(x) {
        return function() {
            var p = fn(x)
            active.push(p.reflect().then(function() {
                active.splice(active.indexOf(p), 1);
            })
            return [Promise.race(active), p];
        }
    }
    function fst(t) {
        return t[0];
    }
    function snd(t) {
        return t[1];
    }
    return function(x) {
        var put = next(x)
        if (active.length < n) {
            var r = put()
            q = fst(t);
            return snd(t);
        } else {
            var r = q.then(put);
            q = r.then(fst);
            return r.then(snd)
        }
    };
}

順便說一句，您可能想看看actor 模型和CSP 。 他們可以簡化處理這些事情，也有一些 JS 庫可供他們使用。

示例

import Promise from 'bluebird'

function sequential(fn) {
  var q = Promise.resolve();
  return (...args) => {
    const p = q.then(() => fn(...args))
    q = p.reflect()
    return p
  }
}

async function _delayPromise (seconds, str) {
  console.log(`${str} started`)
  await Promise.delay(seconds)
  console.log(`${str} ended`)
  return str
}

let delayPromise = sequential(_delayPromise)

async function a() {
  await delayPromise(100, "a:a")
  await delayPromise(200, "a:b")
  await delayPromise(300, "a:c")
}

async function b() {
  await delayPromise(400, "b:a")
  await delayPromise(500, "b:b")
  await delayPromise(600, "b:c")
}

a().then(() => console.log('done'))
b().then(() => console.log('done'))

// --> with sequential()

// $ babel-node test/t.js
// a:a started
// a:a ended
// b:a started
// b:a ended
// a:b started
// a:b ended
// b:b started
// b:b ended
// a:c started
// a:c ended
// b:c started
// done
// b:c ended
// done

// --> without calling sequential()

// $ babel-node test/t.js
// a:a started
// b:a started
// a:a ended
// a:b started
// a:b ended
// a:c started
// b:a ended
// b:b started
// a:c ended
// done
// b:b ended
// b:c started
// b:c ended
// done

Answer 2

使用 throttled-promise 模塊：

https://www.npmjs.com/package/throttled-promise

var ThrottledPromise = require('throttled-promise'),
    promises = [
        new ThrottledPromise(function(resolve, reject) { ... }),
        new ThrottledPromise(function(resolve, reject) { ... }),
        new ThrottledPromise(function(resolve, reject) { ... })
    ];

// Run promises, but only 2 parallel
ThrottledPromise.all(promises, 2)
.then( ... )
.catch( ... );

Answer 3

我有同樣的問題。 我寫了一個庫來實現它。 代碼在這里。 我創建了一個隊列來保存所有的承諾。 當您將一些承諾推送到隊列時，隊列頭部的前幾個承諾將被彈出並運行。 一旦一個承諾完成，隊列中的下一個承諾也將被彈出並運行。 一次又一次，直到隊列中沒有Task 。 您可以查看代碼以了解詳細信息。 希望這個圖書館能幫到你。

Answer 4

優勢

• 您可以定義並發承諾的數量（幾乎同時請求）
• 一致的流程：一旦一個承諾解決，另一個請求開始，無需猜測服務器能力
• 對數據阻塞的魯棒性，如果服務器停止片刻，它只會等待，並且不會因為時鍾允許而啟動下一個任務
• 不要依賴第三方模塊，它是 Vanila node.js

第一件事是讓 https 成為一個承諾，所以我們可以使用等待來檢索數據（從示例中刪除）第二創建一個承諾調度程序，在任何承諾得到解決時提交另一個請求。 3 撥打電話

通過限制並發承諾的數量來限制請求

const https = require('https')

function httpRequest(method, path, body = null) {
  const reqOpt = { 
    method: method,
    path: path,
    hostname: 'dbase.ez-mn.net', 
    headers: {
      "Content-Type": "application/json",
      "Cache-Control": "no-cache"
    }
  }
  if (method == 'GET') reqOpt.path = path + '&max=20000'
  if (body) reqOpt.headers['Content-Length'] = Buffer.byteLength(body);
  return new Promise((resolve, reject) => {
  const clientRequest = https.request(reqOpt, incomingMessage => {
      let response = {
          statusCode: incomingMessage.statusCode,
          headers: incomingMessage.headers,
          body: []
      };
      let chunks = ""
      incomingMessage.on('data', chunk => { chunks += chunk; });
      incomingMessage.on('end', () => {
          if (chunks) {
              try {
                  response.body = JSON.parse(chunks);
              } catch (error) {
                  reject(error)
              }
          }
          console.log(response)
          resolve(response);
      });
  });
  clientRequest.on('error', error => { reject(error); });
  if (body) { clientRequest.write(body)  }  
  clientRequest.end();

  });
}

    const asyncLimit = (fn, n) => {
      const pendingPromises = new Set();

  return async function(...args) {
    while (pendingPromises.size >= n) {
      await Promise.race(pendingPromises);
    }

    const p = fn.apply(this, args);
    const r = p.catch(() => {});
    pendingPromises.add(r);
    await r;
    pendingPromises.delete(r);
    return p;
  };
};
// httpRequest is the function that we want to rate the amount of requests
// in this case, we set 8 requests running while not blocking other tasks (concurrency)


let ratedhttpRequest = asyncLimit(httpRequest, 8);

// this is our datase and caller    
let process = async () => {
  patchData=[
      {path: '/rest/slots/80973975078587', body:{score:3}},
      {path: '/rest/slots/809739750DFA95', body:{score:5}},
      {path: '/rest/slots/AE0973750DFA96', body:{score:5}}]

  for (let i = 0; i < patchData.length; i++) {
    ratedhttpRequest('PATCH', patchData[i].path,  patchData[i].body)
  }
  console.log('completed')
}

process() 

Answer 5

如果您不想使用任何插件/依賴項，則可以使用此解決方案。

假設您的數據在一個名為datas的數組中

1. 創建一個函數來處理datas數組中的數據，我們稱之為processData()
2. 創建一個函數，它將在 while 循環中一個接一個地執行processData() ，直到datas數組上沒有數據為止，讓我們調用該函數bufferedExecution() 。
3. 創建一個大小為buffer_size的數組
4. 用bufferedExecution()填充數組
5. 並等待它在Promise.all()或Promise.allSettled()中解決

這是一個工作示例，其中數據是數字，操作等待一段時間並返回數字的平方，它也隨機拒絕。

 const datas = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]; // this datas array should not contain undefined values for this code to work const buffer_size = 3; const finishedPromises = []; // change this function to your actual function that processes data async function processData(item) { return new Promise((resolve, reject) => { // wait for some time setTimeout(() => { // randomly resolve or reject if (Math.random() > 0.5) { resolve(item ** 2); } else { reject("error message"); } }, 1500); }); } // this function executes one function per loop, but magic happens when you // execute the function below, multiple times async function bufferedExecution(callback, i) { return new Promise(async (resolve, reject) => { // take first vale to process let next = datas.shift(); // check if there is a value, (undefined means you have reached the end of datas array) while (next != undefined) { // just to show which function is running (index of function in array) console.log(`running function id: ${i}`); let result; try { // process data with your function's callback result = await callback(next); // result finishes without error finishedPromises.push({ input: next, result: result, }); } catch (error) { // rejected, so adds error instead of result finishedPromises.push({ input: next, error: error, }); } // get next data from array and goes to next iteration next = datas.shift(); } // once all that is done finish it resolve(); }); } // here is where the magic happens // we run the bufferedExecution function n times where n is buffer size // bufferedExecution runs concurrently because of Promise.all()/Promise.allsettled() const buffer = new Array(buffer_size) .fill(null) .map((_, i) => bufferedExecution(processData, i + 1)); Promise.allSettled(buffer) .then(() => { console.log("all done"); console.log(finishedPromises); // you will have your results in finishedPromises array at this point // you can use input KEY to get the actual processed value // first check for error, if not get the results }) .catch((err) => { console.log(err); });

輸出

// waits a while
running function id: 1
running function id: 2
running function id: 3
// waits a while
running function id: 1
running function id: 2
running function id: 3
// waits a while
running function id: 1
running function id: 2
running function id: 3
// waits a while
running function id: 1
running function id: 2
running function id: 3
// waits a while
running function id: 1
all done
[
  { input: 1, error: 'error message' },
  { input: 2, result: 4 },
  { input: 3, result: 9 },
  { input: 4, result: 16 },
  { input: 5, error: 'error message' },
  { input: 6, result: 36 },
  { input: 7, result: 49 },
  { input: 8, error: 'error message' },
  { input: 9, result: 81 },
  { input: 10, result: 100 },
  { input: 11, result: 121 },
  { input: 12, error: 'error message' },
  { input: 13, result: 169 }
]

Answer 6

串行運行異步進程的經典方法是使用async.js和使用async.series() 。 如果你更喜歡基於 promise 的代碼，那么有一個async.js的 promise 版本： async-q

使用async-q您可以再次使用series ：

async.series([
    function(){return delayPromise(100, "a:a")},
    function(){return delayPromise(100, "a:b")},
    function(){return delayPromise(100, "a:c")}
])
.then(function(){
    console.log(done);
});

同時運行其中兩個將同時運行a和b但在每個內部它們將是順序的：

// these two will run concurrently but each will run
// their array of functions sequentially:
async.series(a_array).then(()=>console.log('a done'));
async.series(b_array).then(()=>console.log('b done'));

如果你想運行b后a接着把它的.then()

async.series(a_array)
.then(()=>{
    console.log('a done');
    return async.series(b_array);
})
.then(()=>{
    console.log('b done');
});

如果您不想按順序運行每個，而是希望限制每個同時運行一定數量的進程，那么您可以使用parallelLimit() ：

// Run two promises at a time:
async.parallelLimit(a_array,2)
.then(()=>console.log('done'));

閱讀 async-q 文檔： https : //github.com/dbushong/async-q/blob/master/READJSME.md