Question

var urlArr = {
    //ex url_for_site0 = 'https://www.google.com'
    url_for_site0,
    url_for_site1,
    url_for_site2,
    url_for_site3,
    ...
    url_for_site50
};

urlArr.forEach(function(url, index) {
    request(url, function(err, res, body) {
        if(err) console.log(index+err);
        else console.log(index+" success");
    });
});

每次执行我的应用时，我都会得到不同的无序结果和错误。

示例：

1 error : socket hang out
21 error : socket hang out
17 error : socket hang out
1 error : socket hang out
19 error : socket hang out
...(omission)
5 success
15 success
45 success
50 success
11 success
37 success

每当我得到结果时，它们的顺序都不同。这是因为我同时打了太多请求吗？当我逐个请求时，没有错误。

示例：

request(url_for_site0)
and restart program
request(url_for_site1)
and restart program
request(url_for_site2)
...

Answer 1

NodeJS事件都在一个池中处理，并且具有非阻塞性质。您可以参考下图。

当我尝试调用多个SQL查询时，它发生在我身上。当我使用C＃完成它时，根本没有问题。但是，NodeJS给了我类似的行为。

nodejs

我不确定这是否是问题的最佳解决方案。但是，这是我如何解决我的SQL调用问题。我使用了异步瀑布函数，以便整个过程变得同步。每个函数将逐个运行，其返回值通过管道传递给下一个函数。所以，你甚至可以做更多的事情。这个库的用法不是很明确，您可以参考此链接以更好地帮助您了解异步瀑布的工作原理，然后使其适合您的解决方案。

https://gist.github.com/dineshsprabu/e6c1cf8f2ca100a8f5ae

以下是我将您的解决方案可视化的方式大致如下：

var async = require('async');

async.waterfall(
[
    function(callback) {
        function_urlArr(url, index, function (returnVal) {
            //Do something with the returnVal
            callback(null, returnVal);
        });

    },
    function(returnVal, callback) {
        //the returnVal from first function gets passed here synchronously
        function_urlArr(url2, index2, function (returnVal) {
            //Do something with the returnVal
            callback(null, returnVal);
        });
    },
    function(returnVal, callback) {
        //and so on ...
    }
],
function (err) {
    //console.log(err);
});

//define your function and enable callback
//you will need to include an extra third argument to receive the callback
function urlArr(url, index, callback) {
    //your code
    return callback(returnValue)
}

Answer 2

由于javascript的non-blocking性质，这种情况正在发生。

如果您希望按顺序逐个实现，可以使用Async函数。

套接字挂断错误可能是因为你接到请求后你点击的网址没有响应。

Answer 3

You might have issue with non-blocking nature of loop forEach. You can combine Promise and aysnc/await to make it blocking. Here is one way of handling it.

const request = require('request');

let urlArr = [
    'https://localhost:9090',
    'https://www.google.com',
    'https://www.ebay.com',
    'https://www.amazon.com',
];

//Creating promise for the requests.
let fetchPromise = function(url) {
    return new Promise((resolve, reject) => {
            request(url, (err, res, body) => {
                if (err)
                    reject(Error(url + ' cannot be fetched'));
                else
                    resolve(body);
            });
        }
    );
};

//creating a blocking function
let fetchAllData = async function(urls) {
    for (url of urls) { //using modern for loop instead for forEach
        try {
            data = await fetchPromise(url); // waiting until promise is resolved.
            console.log('Recieved :' + data.length + 'bytes from ' + url);
        } catch(e) {
            console.log('Error :' + e); // catching error in case promise is rejected
        }              
    }
};

//calling the function
fetchAllData(urlArr);

/*
// In case you want to wait until all promises are resolved.
// Then use Promise.all, however it will fail if any of the promise is rejected.
// One way to handle it would be to modify function fetchPromise such that it 
// always resolves.

Promise
.all(urlArr.map(url => fetchPromise(url)))
.then(data => console.log(data))
.catch(err => console.log(err));
*/

I hope it helps.

请求太多会导致nodejs出错吗？

3 个答案: